Be prepared: how does discontinuous hydration in Tabebuia heterophylla seeds induce stress tolerance in seedlings?

Discontinuous hydration and dehydration (HD) cycles refer to controlled imbibition followed by dehydration before seed germination. Here, we investigated whether the level of imbibition before HD cycles affects the physiology of Tabebuia heterophylla seeds and seedlings. Seeds were imbibed for 10 h (T1; phase I of imbibition) or 35 h (T2; phase II), dehydrated, and progressively rehydrated one to four times (HD cycles). Germination and biochemical parameters (membrane integrity; total soluble, reducing, and nonreducing (NRS) sugars; proteins, amino acids, proline, H2O2, catalase, ascorbate peroxidase, and glutathione reductase activity) were quantified at the last rehydration step of each cycle. Biometric and biochemical parameters (including pigments) were analysed in seedlings 60 days after germination. HD cycles at T1 led to reduced seed germination and greater plasma membrane damage, higher enzyme activity (catalase and glutathione reductase) and accumulation of NRS, total amino acids, and proline compared to the controls and T2 treatment. Cellular damage became more severe with more HD cycles. HD cycles at T2 synchronized germination regardless of the number of cycles and also had a priming effect. T2 seeds had less NRS, total amino acids, and proline content than T1. HD cycles at T1 produced seedlings with higher carotenoid and total chlorophyll content than controls and T2, while seedlings from HD cycles at T2 had higher amounts of osmoprotectants. HD cycles at T2 benefited seeds and seedlings more than at T1. This suggests that the physiological and biochemical effects of HD cycles in seeds modulate seedling plasticity, depending on water availability, potentially promoting increased tolerance to recurrent droughts that will be intensified with ongoing climate changes.

Ion-Fluid Transport-Control Feedback along Nanopore Networks.

Biological signaling correlates with the interrelation between ion and nanofluidic transportation pathways. However, artificial embodies with reconfigurable ion-fluid transport interaction aspects remain largely elusive. Herein, we unveiled an intimate interplay between nanopore-driven advancing flow and ion carriage for the spontaneous imbibition of aqueous solutions at the nanoporous thin film level. Ionic factors dominate transport phenomena processing and integration (ions influence fluid motion, which in turn governs the self-regulated ion traveling). We show an ion-induced translation effect that finely converts a chemical input, the nature of ions, into a related fluidic output: modulation of the extent of imbibition. We further find complex imbibition dynamics induced by the ion type and population. We peculiarly pinpoint a stop-and-go effective transport process with a programmable delay time triggered by selective guest-host interactions. The ion-fluid transport interplay is captured by a simple model that considers the counterbalance between the capillary infiltration and solution concentration, owing to water loss at the nanoporous film-air interface. Our results demonstrate that nanopore networks present fresh scenarios for understanding and controlling autonomous macroscopic liquid locomotion and offer a distinctive working principle for smart ion operation.

Germinación, crecimiento vegetativo y morfología floral de Dasylirion cedrosanum del matorral rosetófilo de Coahuila / Germination, vegetative growth and floral morphology of Dasylirion cedrosanum from the rosetophyllous scrub of Coahuila

RESUMEN El sotol (Dasylirion cedrosanum Trel.), especie endémica del noreste de México, presenta interés económico y social por su aprovechamiento comercial. El objetivo del presente trabajo fue caracterizar la germinación, crecimiento vegetativo y morfología floral de D. cedrosanum del matorral rosetófilo de Coahuila. Se sometieron 3 lotes de 100 semillas a un proceso de imbibición y se registró el porcentaje de germinación. La caracterización de la germinación se realizó a las plántulas cultivadas en laboratorio, mientras que la morfología vegetativa se determinó en plantas adultas tomadas de un jardín botánico, con fecha de siembra conocida y a las cuales no se les dio un manejo de cultivo. La descripción de la morfología floral se realizó en plantas silvestres del cañón de San Lorenzo, Saltillo, Coahuila, México. La primera fase de la imbibición duró 48 h e incrementó 52 % el peso; la segunda o de latencia duró 48 h alcanzando un 55 %; y la tercera concluyó a las 120 h con un incremento total del 60 % de peso. Las semillas emitieron el hipocótilo a partir del quinto día. En el décimo día se obtuvo 98 % de germinación. Entre las características morfológicas distintivas de la especie, las inflorescencias, conocidas como "escapos florales", registraron una altura promedio de 3.39 m. Las flores fueron actinomorfas y unisexuales. La flor estaminada presentó perianto sin diferenciación de tépalos y sépalos. Las flores pistiladas mostraron pedicelos y receptáculo corto. El polen fue elíptico, de abertura monosulcada, con dimensión de 15 μm x 30 μm. Los frutos fueron secos e indehiscentes, conocidos como samara. Las semillas fueron turbinadas de contorno trigonal. El análisis de las características de germinación y morfología vegetativa y floral del sotol permitieron comprender las adaptaciones que esta planta ha desarrollado para crecer en los ambientes semiáridos del país.

ABSTRACT Sotol (Dasylirion cedrosanum Trel.), endemic species of northeastern Mexico, has attracted economic and social interest due to its commercial potencial. The objective of this work was to characterize the germination, vegetative growth and floral morphology of D. cedrosanum from the rosetophyllous scrub of Coahuila. Three batches of 100 seeds were submitted to an imbibition process and the germination percentage was recorded. The characterization of the germination was carried out on the seedlings grown in the laboratory, while the vegetative morphology was determined in adult plants taken from a botanical garden, with a known planting date and which were not given a crop management. The description of the floral morphology was carried out on wild plants from the San Lorenzo canyon, near the municipality of Saltillo, Coahuila, Mexico. The imbibition showed the first phase of absorption within 48 h, with an increase of 52 % in weight. The third phase began at 96 h with an increase of 55 % in weight. The seeds emitted the hypocotyl from the fifth day. On the tenth day 98 % germination was obtained. Among the distinctive morphological characteristics of the species, the inflorescences, known as "floral scapes", recorded an average height of 3.39 m. The flowers were actinomorphic and unisexual. The staminate flower presented perianth without differentiation of tepals and sepals, while the pistillate flowers showed pedicels and a short receptacle. The pollen was elliptical, with a monosulcate opening, with a dimension of 15 μm x 30 μm. The fruits were dry and indehiscent, known as samara. The seeds were turbinated with a trigonal contour. The germination and characteristics of the sotol corresponded to adaptations that allow it to grow in the semi-arid environment of this region of the country.

Seed Priming Based on Iodine and Selenium Influences the Nutraceutical Compounds in Tomato (Solanum lycopersicum L.) Crop.

The use of trace elements in agriculture as a complement to crop fertilization programs is a practice that is gaining importance and relevance worldwide. Iodine and selenium perform essential functions in human health, related to the proper functioning of the thyroid gland, acting as antioxidants and antiproliferatives, and their limited intake through food consumption can cause malnutrition, reflected in the abnormal development and growth of humans. This research aimed to evaluate the nutraceutical quality of tomato (Solanum lycopersicum L.) in response to seed priming based on KIO3 (0, 100, 150, 200, 250 mg L-1) and Na2SeO3 (0, 0.5, 1, 2, 3 mg L-1), performed by interaction from a 52-factorial design and by independent factors in a 24-h imbibition time. The tomato crop was established under greenhouse conditions in 10-L polyethylene containers containing peat moss and perlite 1:1 (v/v). Regarding non-enzymatic antioxidant compounds, lycopene, ß-carotene and flavonoid contents in tomato fruits significantly increased with KIO3 and Na2SeO3 treatments; however, vitamin C content was negatively affected. KIO3 increased the phenol and chlorophyll-a contents of leaves. In relation to enzymatic activity, KIO3 positively influenced GSH content and PAL activity in tomato fruits. KIO3 also positively influenced GSH content in leaves while negatively affecting PAL and APX activities. Na2SeO3 favored GSH content and GPX activity in tomato fruits and leaves. Na2SeO3 negatively affected the antioxidant capacity of hydrophilic compounds by ABTS in fruits and leaves and favored hydrophilic compounds by DPPH in leaves. Seed imbibition based on KIO3 and Na2SeO3 is a method that is implemented in the tomato crop and presents interesting aspects that favor the nutraceutical quality of tomato fruits, which may contribute to increasing the intake of these minerals in humans through tomato consumption.

Pre-Germination Treatments at Operational Scale for Six Tree Species from the Sclerophyll Forest of Central Chile.

Sclerophyll forest in Mediterranean central Chile has been subjected to severe degradation due to anthropic disturbances and climate change and is in need of restoration. Since direct seeding is usually unsuccessful, we need to research seed propagation to produce plants for restoration. Our objective was to assess pre-germination treatments for six native woody species (Acacia caven, Lithraea caustica, Quillaja Saponaria, Porlieria chilensis, Kageneckia angustifolia, and Ceratonia chilensis) of the sclerophyll forest, considering its operational applicability and consequences for nursery plant production. Treatments were selected according to previous studies, and operational applicability in nurseries. Germination and level of seeds water imbibition were assessed. Results indicate that time for seed water imbibition is critical for germination in A. caven, P. chilensis and K. angustifolia, with an average germination of 90.2 ± 2.0%, 85.0 ± 4.7%, and 47.4 ± 2.3%, respectively. Gibberellin did not improve germination compared to water soaking in Q. Saponaria, K. angustifolia and P. chilensis. In addition, physical scarification is a suitable treatment for L. caustica and C. chilensis, instead of chemical scarification, avoiding handling toxic and corrosive compounds in nurseries. We recommend assessing seed water imbibition rates as a key factor for proper germination processes.

Acceleration in Germination Sensu stricto Plays a Central Role on Seedling Vigor in Post-Germination.

An obvious relationship between germination sensu stricto and seedling development during post-germination has been considered, but not explained concerning vigor. Taking this into account, we used measurements of water dynamics in germinating seeds and seedling development to clarify that relationship. The biological model was soybean seeds, since it is the most relevant 'true seed' produced around world. Our findings suggest that the way energy is used (acceleration) and not its input (velocity) is the main aspect relating seed germination and seedling development, especially when considering vigor. However, velocity and acceleration can be complementary in analyses of seed physiology. Other measurements proposed here also have potential uses for testing vigor in seed lots, such as seedling vigor index and biological activity in the lot. Therefore, water dynamics in germinating seeds can be an interesting way for testing seed lots, because it is an easier, faster and cheaper method in relation to other non-destructive procedures.

Water uptake dynamics in soybean seeds: influence in seeds performance and DNA integrity / Dinâmica de absorção de água em sementes de soja: influência no desempenho de sementes e integridade do DNA

Relationships among water uptake rate and temperatures were investigated in five soybean seeds lots cv. M 6410 IPRO. Germination, field emergence and electrical conductivity tests were applied to determine seed performance after fast (complete immersion in water), control (moist substrate) and slow (moist atmosphere) imbibitions both at 20 °C and 30 °C. The fresh weight increment over time in soybean seeds during imbibition was recorded. In parallel, analysis of the DNA integrity of seedlings obtained from such seeds was performed in gel electrophoresis. Absorption pattern of soybean seeds were similar among temperatures, but absorption characteristics vary with time progress according to the way of water entrance into the seeds. Upon fast imbibition seeds germinated lower than non-fast-imbibed seeds, besides loss of seed performance. In contrast, slow-imbibed seeds showed high germination, low abnormal seedlings and maintenance of seeds performance. DNA isolation from fast imbibed seeds was highly degraded; although, some considerably degraded samples were reported in controlled imbibed seeds and the best preserved DNA was found in slow-imbibed seeds. The pattern of DNA degradation is typically passive or non programmed cell death. Our results showed it is important to consider the water uptake rate during germination test, since DNA integrity plays a critical role during seed imbibition, preserving soybean seed performance.(AU)

As relações entre a taxa de embebição em água e temperaturas foram estudadas em cinco lotes de sementes de soja cv. M 6410 IPRO. Testes de germinação, emergência a campo e condutividade elétrica foram aplicados para avaliar o desempenho das sementes após rápida embebição (imersão direta em água), controlada (substrato úmido) e lenta (atmosfera úmida), ambos a 20 °C e 30 °C. O incremento no peso fresco das sementes durante a embebição foi registrado. Paralelamente, a integridade do DNA de plântulas oriundas das sementes foi avaliado em gel por eletroforese. O padrão de embebição das sementes de soja foi similar entre as temperaturas, mas houve variações com o tempo de acordo com o modo de entrada de água nas sementes. Após a embebição rápida, as sementes apresentam menor germinação e desempenho que as sementes submetidas aos demais métodos de embebição. O DNA isolado a partir de sementes que embeberam rapidamente encontrava-se degradado, embora em sementes que foram hidratadas de forma controlada também fosse encontrada degradação do DNA. O DNA mais preservado foi encontrado em sementes que embebem lentamente. O padrão de degradação do DNA é típico de morte passiva ou não programada de células. Os resultados indicam que é importante considerar a taxa de embebição em água durante o teste de germinação, pois a integridade do DNA desempenha uma função importante durante a embebição, preservando o desempenho das sementes de soja.(AU)

Water uptake dynamics in soybean seeds: influence in seeds performance and DNA integrity / Dinâmica de absorção de água em sementes de soja: influência no desempenho de sementes e integridade do DNA

ABSTRACT: Relationships among water uptake rate and temperatures were investigated in five soybean seeds lots cv. M 6410 IPRO. Germination, field emergence and electrical conductivity tests were applied to determine seed performance after fast (complete immersion in water), control (moist substrate) and slow (moist atmosphere) imbibitions both at 20 °C and 30 °C. The fresh weight increment over time in soybean seeds during imbibition was recorded. In parallel, analysis of the DNA integrity of seedlings obtained from such seeds was performed in gel electrophoresis. Absorption pattern of soybean seeds were similar among temperatures, but absorption characteristics vary with time progress according to the way of water entrance into the seeds. Upon fast imbibition seeds germinated lower than non-fast-imbibed seeds, besides loss of seed performance. In contrast, slow-imbibed seeds showed high germination, low abnormal seedlings and maintenance of seeds performance. DNA isolation from fast imbibed seeds was highly degraded; although, some considerably degraded samples were reported in controlled imbibed seeds and the best preserved DNA was found in slow-imbibed seeds. The pattern of DNA degradation is typically passive or non programmed cell death. Our results showed it is important to consider the water uptake rate during germination test, since DNA integrity plays a critical role during seed imbibition, preserving soybean seed performance.

RESUMO: As relações entre a taxa de embebição em água e temperaturas foram estudadas em cinco lotes de sementes de soja cv. M 6410 IPRO. Testes de germinação, emergência a campo e condutividade elétrica foram aplicados para avaliar o desempenho das sementes após rápida embebição (imersão direta em água), controlada (substrato úmido) e lenta (atmosfera úmida), ambos a 20 °C e 30 °C. O incremento no peso fresco das sementes durante a embebição foi registrado. Paralelamente, a integridade do DNA de plântulas oriundas das sementes foi avaliado em gel por eletroforese. O padrão de embebição das sementes de soja foi similar entre as temperaturas, mas houve variações com o tempo de acordo com o modo de entrada de água nas sementes. Após a embebição rápida, as sementes apresentam menor germinação e desempenho que as sementes submetidas aos demais métodos de embebição. O DNA isolado a partir de sementes que embeberam rapidamente encontrava-se degradado, embora em sementes que foram hidratadas de forma controlada também fosse encontrada degradação do DNA. O DNA mais preservado foi encontrado em sementes que embebem lentamente. O padrão de degradação do DNA é típico de morte passiva ou não programada de células. Os resultados indicam que é importante considerar a taxa de embebição em água durante o teste de germinação, pois a integridade do DNA desempenha uma função importante durante a embebição, preservando o desempenho das sementes de soja.

[D-Leu1]MC-LR and MC-LR: A Small-Large Difference: Significantly Different Effects on Phaseolus vulgaris L. (Fabaceae) Growth and Phototropic Response after Single Contact during Imbibition with Each of These Microcystin Variants.

[D-Leu1]MC-LR and MC-LR, two microcystins differing in one amino acid, constitute a sanitary and environmental problem owing to their frequent and concomitant presence in water bodies of the Americas and their association with human intoxication during recreational exposure to cyanobacterial bloom. Present in reservoirs used for irrigation as well, they can generate problems in the development of crops such as Phaseolus vulgaris, of nutritional and economic interest to the region. Although numerous works address the toxic effects of MC-LR, information on the toxicity of [D-Leu1]MC-LR is limited. Our objective was to study the toxic effects of [D-Leu1]MC-LR and MC-LR (3.5 µg/ml) on P. vulgaris after a single contact at the imbibition stage. Our findings indicate that 10 days post treatment, [D-Leu1]MC-LR generates morphological and physiological alterations more pronounced than those caused by MC-LR. In addition to the alterations produced by [D-Leu1]MC-LR in the development of seedlings and the structure of the leaves, roots and stems, we also found alterations in leaf stomatal density and conductivity, a longer delay in the phototropic response and a decrease in the maximum curvature angles achieved with respect to that observed for MC-LR. Our findings indicate that these alterations are linked to the greater inhibition of phosphatase activity generated by [D-Leu1]MC-LR, rather than to oxidative damage. We observed that 30 days after treatment with MC-LR, plants presented better development and recovery than those treated with [D-Leu1]MC-LR. Further studies are required on [D-Leu1]MC-LR and MC-LR toxicity and their underlying mechanisms of action.

Secondary-cell-wall release: a particular pattern of secretion in the mucilaginous seed coat of Magonia pubescens.

PREMISE: Plant mucilages are composed of strongly hydrophilic polysaccharides and contribute to seed germination and seedling establishment. The myxospermic seeds of Magonia pubescens, a Cerrado (neotropical savanna) tree species, produces a voluminous mucilage capsule when hydrated. The development of the mucilaginous layer, the process of mucilage secretion and its role in seed germination was not previously studied so far. METHODS: Morphological, anatomical, histochemical, and ultrastructural evaluations of the seed coat during seed development were undertaken. The formation of the mucilage capsule was followed using scanning electron microscopy, and the coat's effects on seed hydration and germination were evaluated after experimental manipulation of the seed coat. RESULTS: The mucilaginous layer is contained in the outer coat of the seed. The mucilage-secreting cells accumulate proteins in the outer periclinal region and acidic polysaccharides in the inner periclinal region of the periplasmic space. Neutral polysaccharides, which form the loosely organized secondary wall, form a folding, basket-like structure surrounding the acidic polysaccharides. The protoplast collapses at maturity. With hydration, the mucilage expands, breaks the epidermal layer, and forms a mucilage capsule around the seed. The mucilaginous seed coat does not increase the germination rate. CONCLUSIONS: Upon mucilage hydration, the secondary cell walls forming the network of neutral polysaccharides are released, along with proteins, and help retain the acidic polysaccharides-forming a peculiar architecture that imparts integrity and consistency to the mucilage capsule. As winged seeds are not usually buried, the mucilage capsule favors seedling hydration, contributing to its establishment on the soil surface.

GERMINACIÓN DE SEMILLAS DE MORINGA (Moringa oleifera Lam.) EN DIFERENTES TIEMPOS DE IMBIBICIÓN EN AGUA

La siembra del cultivo de moringa con semillas gámicas tiene ventajas sobre la propagación vegetativa con estacas, por la buena disponibilidad de semillas, rapidez en la fase de semillero, facilidad de trasplante, economía en las labores y mejor anclaje definitivo; sin embargo, se ha reportado que las semillas maduras presentan bajo porcentaje de germinación, por lo cual, se hizo una investigación en la Universidad de Córdoba, Colombia, con el objetivo de establecer el efecto de la imbibición de semillas en agua sobre el porcentaje de germinación. Se hizo un bioensayo con semillas extraídas de un árbol de un año de edad, sembrado en el campo experimental de cultivos de hortalizas. El diseño experimental utilizado fue completamente al azar y se aplicaron tres tratamientos: semillas embebidas en agua 24h, semillas embebidas en agua 48h y semillas embebidas en agua 72h, teniendo como testigo semillas sin imbibición en agua. Los datos de porcentaje de germinación PG se ajustaron al modelo logístico y se obtuvieron la velocidad absoluta de germinación VAG y velocidad relativa de germinación VRG. De acuerdo con los resultados, se estableció que, a mayor tiempo de imbibición de las semillas, se disminuyó el porcentaje de germinación, desde 66 hasta 29% y la velocidad absoluta de germinación, desde 29 semillas∙día-1 hasta 7 semillas∙día-1.

Sowing of the moringa crop with gamic seeds has advantages over vegetative propagation with stakes due to the good availability of seeds, rapidity in the nursery phase, ease of transplantation, economy in the work and best definitive anchorage. However, it has been reported that mature seeds have a low percentage of germination, therefore a research was made at the Universidad de Córdoba, Colombia, with the objective of establishing the effect of the imbibition of seeds in water on germination percentage. A bioassay with seeds extracted from a one year old tree, planted in the experimental field of vegetable crops was carried out. The experimental design used was completely randomized and three treatments were applied, seed imbibition in water during 24h, seed imbibition in water during 48h and seed imbibition in water during 72h having as control seeds without imbibition in water. The germination percentage GP data were adjusted to the logistic model and the absolute rate of germination ARG and relative rate of germination RRG were obtained. According to the results it was established that the GP decreased at a longer seed imbibition time and AGR decreased from 29 seeds∙day-1 to 7 seeds∙day-1.

Roles of mucilage in Emilia fosbergii, a myxocarpic Asteraceae: Efficient seed imbibition and diaspore adhesion.

PREMISE OF THE STUDY: Several angiosperm families have myxodiaspory, such as the Asteraceae in which cypselae are frequently wind-dispersed. The roles of mucilage in cypselae remain misunderstood, and the route of water uptake from substrate to embryo remains unknown. In this work, we analyze the fruits of Emilia fosbergii aiming to clarify how the water is absorbed and how the structure of the pericarp can be related to the processes of diaspore adhesion and seed imbibition. METHODS: The anatomy and ultrastructure of the cypselae of Emilia fosbergii were analyzed with histochemical tests and light, scanning and transmission electron microscopy. We assessed the roles of mucilage in seed imbibition using apoplasmic tracing with Lucifer yellow and epifluorescence microscopy and in adhesion with a sand assay. KEY RESULTS: We describe structural and ultrastructural aspects of the exocarpic cells, especially the mucilaginous twin hairs. Lucifer yellow was absorbed only by the twin hairs, the cells where water primarily enters the seed during seed imbibition. In the sand assay, the mucilage was adhesive. CONCLUSIONS: The twin hairs on the surface of the cypselae can play a dual role in the establishment of new plants of this species. First, these trichomes constitute the main passage for water intake, which is essential for seed imbibition and germination, and after imbibition, they release mucilage that can adhere the diaspore. Therefore, the presence of myxocarpy in Asteraceae could be important in anemochoric species to avoid secondary dispersal.

Cold tolerance in rice germinating seeds revealed by deep RNAseq analysis of contrasting indica genotypes.

Rice productivity is largely affected by low temperature, which can be harmful throughout plant development, from germination to grain filling. Germination of indica rice cultivars under cold is slow and not uniform, resulting in irregular emergence and small plant population. To identify and characterize novel genes involved in cold tolerance during the germination stage, two indica rice genotypes (sister lines previously identified as cold-tolerant and cold-sensitive) were used in parallel transcriptomic analysis (RNAseq) under cold treatment (seeds germinating at 13 °C for 7 days). We detected 1,361 differentially expressed transcripts. Differences in gene expression found by RNAseq were confirmed for 11 selected genes using RT-qPCR. Biological processes enhanced in the cold-tolerant seedlings include: cell division and expansion (confirmed by anatomical sections of germinating seeds), cell wall integrity and extensibility, water uptake and membrane transport capacity, sucrose synthesis, generation of simple sugars, unsaturation of membrane fatty acids, wax biosynthesis, antioxidant capacity (confirmed by histochemical staining of H2O2), and hormone and Ca(2+)-signaling. The cold-sensitive seedlings respond to low temperature stress increasing synthesis of HSPs and dehydrins, along with enhanced ubiquitin/proteasome protein degradation pathway and polyamine biosynthesis. Our findings can be useful in future biotechnological approaches aiming to cold tolerance in indica rice.

Loss of desiccation tolerance in Copaifera langsdorffii Desf. seeds during germination / Perda da tolerância à dessecação em sementes de Copaifera langsdorffii durante a germinação

This study evaluated the loss of desiccation tolerance in C. langsdorffii seeds during the germination process. Seeds were imbibed for 24, 48, 72, 96, 120 and 144 hours and dried to the initial moisture content, kept in this state for 3 days after which they were submitted to pre-humidification and rehydration. Ultraestructural evaluations were done aiming to observe the cell damage caused by the dry process. Desiccation tolerance was evaluated in terms of the percentage of normal seedlings. Seeds not submitted to the drying process presented 61% of normal seedlings, and after 24 hours of imbibition, followed by drying, the seeds presented the same percentage of survival. However, after 48 hours of imbibition, seeds started to lose the desiccation tolerance. There was twenty six percent of normal seedlings formed from seeds imbibed for 96 hours and later dried and rehydrated. Only 5% of seeds imbibed for 144 hours, dried and rehydrated formed normal seedlings. At 144 hours of imbibition followed the dry process, there was damage into the cell structure, indicating that the seeds were unable to keep the cell structure during the drying process. Copaifera langsdorffii seeds loses the desiccation tolerance at the start of Phase 2 of imbibition.

Este estudo avaliou a perda da tolerância à dessecação em sementes de C. langsdorffii durante o processo germinativo. Sementes foram embebidas por 24, 48, 72, 96, 120 e 144 horas e depois secas até a umidade inicial, sendo mantidas neste estado durante 3 dias, quando então foram submetidas a pré-umidificação e reidratação. Avaliações ultraestruturais foram realizadas objetivando observar danos nas células causados pelo processo de secagem. A tolerância à dessecação foi avaliada pelo percentual de plântulas normais. Sementes não submetidas ao processo de secagem apresentaram 61% de plântulas normais, sendo que após 24 horas de embebição seguida de secagem, houve o mesmo percentual de sobrevivência. Contudo, após 48 horas de embebição, as sementes começaram a perder a tolerância à dessecação. Vinte e seis por cento de sementes formaram plântulas normais após embeberem por 96 horas e secas. Apenas 5% de sementes embebidas por 144 horas e secas formaram plântulas normais. Após 144 horas de embebição, seguida de secagem, verificou-se danos na estrutura celular, o que indica que as sementes não são capazes de manter a estrutura celular durante o processo de secagem. Verificou-se no presente estudo que sementes de C. langsdorffii perdem a tolerância à dessecação no inicio da fase 2 da embebição.

Fruits and seeds biometry and pre-germination treatments in Cassia fistula L. (Fabaceae-Caesalpinioideae) / Biometria de frutos e sementes e tratamentos pré-germinativos em Cassia fistula L. (Fabaceae-Caesalpinioideae)

This study aimed to characterize the morphology of fruits and seeds of Cassia fistula L. (Fabaceae) and study techniques, mechanics and physics as pre-germination of seeds of these species treatments. Measurements of length, diameter, thickness, fresh weight and number of seeds per fruit were taken at a sample of 100 fruits, selected at random from the lot of the municipality of Souza-PB. After extraction of seeds from fruits withdrew randomly sample of 100 seedlings for the determination of length, diameter, width, fresh weight, mass of 1,000 seeds and humidity. To overcome dormancy were used the following techniques: without scarification and scarified cheeks and side opposite to the hilum, and these mechanical treatments with and without soaking in distilled water for 12 to 24 hours, using 100 seeds per treatment divided in four replications. After application of the treatments, the seeds has been were sown in trays containing autoclaved sand. The effectiveness treatments measured by variables: first count, emergency, rate of emergence, mean time of emergence and length and dry weight of shoots and roots of seedlings. Fruits and seeds of C. fistula have, on average, 414 and 8.28 mm in length; 18.9 and 6.25 mm in diameter; 20.9 and 3.54 mm in thickness and; 67.3 and 0.1474 g of fresh, respectively. The scarification is efficient to overcome the dormancy of C. fistula, rising above 90 and 50% variablesemergence and seedling growth, respectively. The soaking in water for 24 hours does not promotebreaking dormancy. Scarification improves emergence and seedling vigor of C. fistula.(AU)

Este trabalho objetivou caracterizar a morfometria de frutos e sementes de Cassia fistula L. (Fabaceae) e estudar técnicas, mecânica e física, como tratamentos pré-germinativos das sementes desta espécie. As medidas de comprimento, diâmetro, espessura, massa fresca e número de sementes por fruto foram tomadas em uma amostra de 100 frutos, retirada aleatoriamente do lote coletado no município de Souza- PB. Após a extração das sementes dos frutos retirou-se, aleatoriamente, amostra de 100 propágulos para as determinações de comprimento, diâmetro, largura, massa fresca, massa de 1.000 sementes e umidade. Para a superação da dormência foram empregadas as seguintes técnicas: sem escarificação e escarificadas nas faces lateral e oposta ao hilo, sendo estes tratamentos mecânicos sem e com embebição em água destilada por 12 e 24 horas, utilizando-se 100 sementes por tratamento, divididas em quatro repetições. Após aplicação dos tratamentos, as sementes foram semeadas em areia autoclavada. A eficiência dos tratamentos foi avaliada pelas varáveis: primeira contagem da emergência, emergência, índice de velocidade da emergência, tempo médio da emergência e comprimento e biomassa seca da parte aérea e radicular das plântulas. Frutos e sementes de C. fistula possuem, em média, 414 e 8,28 mm de comprimento; 18,9 e 6,25 mm de diâmetro; 20,9 e 3,54 mm de espessura e; 67,3 e 0,1474 g de massa fresca, respectivamente. As escarificações são eficiente para superar a dormência de sementes de C. fistula, aumentando acima de 90 e 50% para as variáveis de emergência e crescimento das plântulas, respectivamente. A embebição em água por até 24 horas não promove superação de dormência. A escarificação aumenta a emergência e o vigor das plântulas de C. fistula.(AU)

Fruits and seeds biometry and pre-germination treatments in Cassia fistula L. (Fabaceae-Caesalpinioideae) / Biometria de frutos e sementes e tratamentos pré-germinativos em Cassia fistula L. (Fabaceae-Caesalpinioideae)

This study aimed to characterize the morphology of fruits and seeds of Cassia fistula L. (Fabaceae) and study techniques, mechanics and physics as pre-germination of seeds of these species treatments. Measurements of length, diameter, thickness, fresh weight and number of seeds per fruit were taken at a sample of 100 fruits, selected at random from the lot of the municipality of Souza-PB. After extraction of seeds from fruits withdrew randomly sample of 100 seedlings for the determination of length, diameter, width, fresh weight, mass of 1,000 seeds and humidity. To overcome dormancy were used the following techniques: without scarification and scarified cheeks and side opposite to the hilum, and these mechanical treatments with and without soaking in distilled water for 12 to 24 hours, using 100 seeds per treatment divided in four replications. After application of the treatments, the seeds has been were sown in trays containing autoclaved sand. The effectiveness treatments measured by variables: first count, emergency, rate of emergence, mean time of emergence and length and dry weight of shoots and roots of seedlings. Fruits and seeds of C. fistula have, on average, 414 and 8.28 mm in length; 18.9 and 6.25 mm in diameter; 20.9 and 3.54 mm in thickness and; 67.3 and 0.1474 g of fresh, respectively. The scarification is efficient to overcome the dormancy of C. fistula, rising above 90 and 50% variablesemergence and seedling growth, respectively. The soaking in water for 24 hours does not promotebreaking dormancy. Scarification improves emergence and seedling vigor of C. fistula.

Este trabalho objetivou caracterizar a morfometria de frutos e sementes de Cassia fistula L. (Fabaceae) e estudar técnicas, mecânica e física, como tratamentos pré-germinativos das sementes desta espécie. As medidas de comprimento, diâmetro, espessura, massa fresca e número de sementes por fruto foram tomadas em uma amostra de 100 frutos, retirada aleatoriamente do lote coletado no município de Souza- PB. Após a extração das sementes dos frutos retirou-se, aleatoriamente, amostra de 100 propágulos para as determinações de comprimento, diâmetro, largura, massa fresca, massa de 1.000 sementes e umidade. Para a superação da dormência foram empregadas as seguintes técnicas: sem escarificação e escarificadas nas faces lateral e oposta ao hilo, sendo estes tratamentos mecânicos sem e com embebição em água destilada por 12 e 24 horas, utilizando-se 100 sementes por tratamento, divididas em quatro repetições. Após aplicação dos tratamentos, as sementes foram semeadas em areia autoclavada. A eficiência dos tratamentos foi avaliada pelas varáveis: primeira contagem da emergência, emergência, índice de velocidade da emergência, tempo médio da emergência e comprimento e biomassa seca da parte aérea e radicular das plântulas. Frutos e sementes de C. fistula possuem, em média, 414 e 8,28 mm de comprimento; 18,9 e 6,25 mm de diâmetro; 20,9 e 3,54 mm de espessura e; 67,3 e 0,1474 g de massa fresca, respectivamente. As escarificações são eficiente para superar a dormência de sementes de C. fistula, aumentando acima de 90 e 50% para as variáveis de emergência e crescimento das plântulas, respectivamente. A embebição em água por até 24 horas não promove superação de dormência. A escarificação aumenta a emergência e o vigor das plântulas de C. fistula.

Morpho-anatomy, imbibition, viability and germination of the seed of Anadenanthera colubrina var. cebil (Fabaceae) / Morfo-anatomía, imbibición, viabilidad y germinación de las semillas de Anadenanthera colubrina var. cebil (Fabaceae)

Seed biology is a relevant aspect of tropical forests because it is central to the understanding of processes of plant establishment, succession and natural regeneration. Anadenanthera colubrina var. cebil is a timber tree from South America that produces large seeds with thin weak teguments, which is uncommon among legumes. This study describes the morphology and anatomy of the seed coat, the viability, imbibition, and germination in this species. Seeds used during the essays came from 10 trees that grow naturally in Horco Molle, province of Tucumán, Argentina. Seed morphology was described from a sample of 20 units. The seed coat surface was examined with a scanning electron microscope. Transverse sections of hydrated and non-hydrated seeds were employed to describe the histological structure of the seed coat. Hydration, viability and germination experiments were performed under laboratory controlled conditions; and the experimental design consisted of 10 replicas of 10 seeds each. Viability and germination tests were conducted using freshly fallen seeds and seeds stored for five months. Morphologically the seeds of A. colubrina var. cebil are circular to subcircular, laterally compressed, smooth, bright brown and have a horseshoe fissure line (=pleurogram) on both sides. The seed coat comprises five tissue layers and a double (external and internal) cuticle. The outer cuticle (on the epidermis) is smooth and interrupted by microcracks and pores of variable depth. The epidermis consists of macroesclereids with non-lignified secondary walls. This layer is separated from the underlying ones during seed hydration. The other layers of internal tissues are comprised of osteosclereids, parenchyma, osteosclereids, and macrosclereids. The percentage of viable seeds was 93%, decreasing to 75% in seeds with five months old. Seed mass increased 76% after the first eight hours of hydration. Germination percentage was 75% after 76 hours. Germination of seeds stored for five months decreased to 12%. The results showed that seeds of A. colubrina var. cebil are highly permeable and germinate directly without a dormant period.

El cebil, Anadenanthera colubrina var. cebil (Griseb.) Altschul, es un árbol forestal de América del Sur con grandes semillas de tegumentos delgados y débiles. Este estudio describe la morfología y anatomía de la cubierta seminal del cebil y evalúa la viabilidad, la imbibición y germinación de las semillas. Morfológicamente las semillas son circulares a subcirculares, comprimidas lateralmente, lisas, marrón lustrosas, con una línea fisural en forma de herradura en ambas caras. Histológicamente la cubierta seminal comprende cinco capas de células y una cutícula externa e interna. La cutícula externa es lisa y presenta microfisuras y poros de profundidad variable. La epidermis consiste de un estrato de macroesclereidas con paredes secundarias no lignificadas. Los siguientes tejidos internos incluyen, osteosclereidas, parénquima, osteoscleridas y macroesceleridas. El porcentaje de semillas viables fue del 93%, disminuyendo al 75% en semillas con cinco meses de almacenamiento. Las semillas incrementaron el 76% de su masa durante las primeras 8 horas de hidratación. El porcentaje de germinación en semillas nuevas fue del 75% al término de 76 horas y del 12% en semillas almacenadas por cinco meses. Los resultados confirman que las semillas de A. colubrina var. cebil son altamente permeables y germinan sin un período de reposo.

Potencial fisiológico de sementes de girassol influenciado pelo umedecimento artificial / Physiological potential of sunflower seeds as by the artificial moistening

O objetivo do trabalho foi avaliar a qualidade fisiológica de sementes de girassol após a hidratação pelos métodos da atmosfera úmida e substrato úmido em temperaturas de 10 e 20°C visando a elevar o teor de água das sementes a 15, 20 e 25%. A qualidade fisiológica inicial e após o umedecimento das sementes foi determinada por testes de germinação e vigor (primeira contagem da germinação, germinação a baixa temperatura, emergência e índice de velocidade de emergência de plântulas em areia, massa de matéria seca e comprimento de plântulas). O método do substrato úmido a 10°C visando a aumentar o teor de água a 15 e 20% foi favorável em sementes de elevada qualidade, embora com redução do vigor das plântulas.

The objective of this study was to evaluate the sunflower seeds physiological quality after hydration by the moist atmosphere and moist substrate methods at temperatures of 10 and 20°C aiming to the water content of seeds at 15, 20 and 25%. The initial physiological quality and after the wetting of the seeds was determined by testing germination and vigor (first count of germination, germination at low temperature, emergence speed index and seedling emergence in sand, dry weight and length of seedlings). The method of moist substrate at 10°C to increase the water content at 15 and 20% was positive for moistening the seeds of high quality, although it has been observed small decrease seedling vigor.

Armazenamento de sementes tratadas com cloreto de mepiquat e desenvolvimento de plântulas de algodoeiro / Processing of seeds treated with mepiquat chloride and the development of cotton seedlings

O tratamento de sementes de algodão com regulador de crescimento é utilizado para a obtenção de plantas com menor estatura, com a vantagem de assegurar o controle do desenvolvimento vegetativo desde a emergência. O objetivo deste trabalho foi avaliar o desenvolvimento de plântulas de algodoeiro, provenientes de sementes tratadas com cloreto de mepiquat, em diferentes doses, formas de aplicação e armazenadas após o tratamento. Sementes da cultivar 'IPR 120' foram tratadas com soluções de cloreto de mepiquat nas doses zero; 5; 10; 15 e 20g i.a kg-1 de sementes, via embebição por 12 horas e via aplicação direta nas sementes. As sementes tratadas foram armazenadas em condições ambientais de laboratório e avaliadas mensalmente até 180 dias. Foram avaliados germinação, comprimentos da parte aérea, radicular e total e a massa seca das plântulas. Os dados, para cada período de armazenamento, foram submetidos à análise de variância e as médias de formas de aplicação comparadas pelo teste de Tukey a 5%, em delineamento inteiramente casualizado, com quatro repetições, em esquema fatorial de 5x2 (doses x formas de aplicação). Os dados de doses foram submetidos a estudos de regressão até 2° grau. Sementes tratadas com cloreto de mepiquat, independente da forma e dose utilizada podem ser armazenadas por até 180 dias após o tratamento sem comprometer o processo de germinação e a ação do regulador de crescimento. O tratamento via embebição de sementes com o cloreto de mepiquat proporciona maior redução do crescimento da plântula em relação à aplicação direta. O incremento nas doses de cloreto de mepiquat provoca a redução no crescimento e desenvolvimento das plântulas de algodoeiro, proporcionando menor comprimento e massa seca.

The treatment of cotton seeds with growth regulator is used to obtain plants with reduced stature, with the advantage of ensuring control of plant development from emergence. The objective was to evaluate the development of cotton seedlings, grown from seeds treated with chloride mepiquat at different doses, application forms and stored after treatment. The seeds were treated with '120 IPR' solutions mepiquat chloride at doses of zero, 5, 10, 15 and 20g a. i kg-1 seed, via soaking for 12 hours and via direct application in seed. The treated seeds were stored in laboratory conditions and evaluated monthly until 180 days. We evaluated the germination, the length of shoot, root and total, the dry weight of seedlings. The data for each storage period, were subjected to analysis of variance and means of application methods were compared by Tukey test at 5%, under the completely randomized design with four replications in a factorial 5x2 (doses x application forms). The data were subjected to doses of regression studies until 2nd grade. Seeds treated with mepiquat chloride, independent of dose and can be stored for up to 180 days after treatment, without compromising the process of germination and growth regulator action. Treatment via soaking of seeds with mepiquat chloride provides the greatest reduction in seedling growth in relation to direct application. The increased rate of mepiquat chloride causes the reduction the growth and development of cotton seedlings, providing less length and dry mass.

Critical points in logistic growth curves and treatment comparisons

Several biological phenomena have a behavior over time mathematically characterized by a strong increasing function in the early stages of development, then by a less pronounced growth, sometimes showing stability. The separation between these phases is very important to the researcher, since the maintenance of a less productive phase results in uneconomical activity. In this report we present methods of determining critical points in logistic functions that separate the early stages of growth from the asymptotic phase, with the aim of establishing a stopping critical point in the growth and on this basis determine differences in treatments. The logistic growth model is fitted to experimental data of imbibition of araribá seeds (Centrolobium tomentosum). To determine stopping critical points the following methods were used: i) accelerating growth function, ii) tangent at the inflection point, iii) segmented regression; iv) modified segmented regression; v) non-significant difference; and vi) non-significant difference by simulation. The analysis of variance of the abscissas and ordinates of the breakpoints was performed with the objective of comparing treatments and methods used to determine the critical points. The methods of segmented regression and of the tangent at the inflection point lead to early stopping points, in comparison with other methods, with proportions ordinate/asymptote lower than 0.90. The non-significant difference method by simulation had higher values of abscissas for stopping point, with an average proportion ordinate/asymptote equal to 0.986. An intermediate proportion of 0.908 was observed for the acceleration function method.