Effects of increasing atmospheric CO2 on leaf water δ18O values are small and are attenuated in grasses and amplified in dicotyledonous herbs and legumes when transferred to cellulose δ18O values.

The oxygen isotope composition of cellulose (δ18O values) has been suggested to contain information on stomatal conductance (gs) responses to rising pCO2. The extent by which pCO2 affects leaf water and cellulose δ18O values (δ18OLW and δ18OC) and the isotope processes that determine pCO2 effects on δ18OLW and δ18OC are, however, unknown. We tested the effects of pCO2 on gs, δ18OLW and δ18OC in a glasshouse experiment, where six plant species were grown under pCO2 ranging from 200 to 500 ppm. Increasing pCO2 caused a decline in gs and an increase in δ18OLW, as expected. Importantly, the effects of pCO2 on gs and δ18OLW were small and pCO2 effects on δ18OLW were not directly transferred to δ18OC but were attenuated in grasses and amplified in dicotyledonous herbs and legumes. This is likely because of functional group-specific pCO2 effects on the model parameter pxpex. Our study highlights important uncertainties when using δ18OC as a proxy for gs. Specifically, pCO2-triggered gs effects on δ18OLW and δ18OC are possibly too small to be detected in natural settings and a pCO2 effect on pxpex may render the commonly assumed negative linkage between δ18OC and gs to be incorrect, potentially confounding δ18OC based gs reconstructions.

Arbuscular mycorrhizal fungi activity in the rhizosphere of tree seedlings subjected to residual herbicides / Atividade de fungos micorrízicos arbusculares na rizosfera de mudas de árvores submetidas a herbicidas residuais

Trees occurring on the margins of agricultural areas can mitigate damage from residual herbicides. Rhizospheric microbial activity associated with trees is one of the main remedial capacity indicators. The objective of this study was to evaluate the rhizospheric microbiological activity in tree species subjected to the herbicides atrazine and sulfentrazone via the rhizosphere. The experiment was designed in four blocks and a 6 × 3 factorial scheme. The first factor consisted of six tree species from Brazil and the second of atrazine, sulfentrazone, and water solutions. Four herbicide applications were performed via irrigation. The total dry mass of the plants, mycorrhizal colonization, number of spores, basal respiration of the rhizospheric soil, and survival rate of bioindicator plants after phytoremediation were determined. Trichilia hirta had higher biomass when treated with atrazine and sulfentrazone. Herbicides decreased the microbial activity in Triplaris americana and did not affect the microbiological indicators of Myrsine gardneriana, Schizolobium parahyba, and Toona ciliata. Fewer bioindicator plants survived in soil with Triplaris americana and sulfentrazone. Microbiological indicators were influenced in different ways between species by the presence of herbicides in the rhizosphere.

As árvores que ocorrem nas margens das áreas agrícolas podem mitigar os danos dos herbicidas residuais. A atividade microbiana rizosférica associada às árvores é um dos principais indicadores de capacidade corretiva. O objetivo deste trabalho foi avaliar a atividade microbiológica rizosférica em espécies arbóreas submetidas aos herbicidas atrazina e sulfentrazone via rizosfera. O experimento foi estruturado em quatro blocos e esquema fatorial 6 × 3. O primeiro fator consistiu em seis espécies de árvores do Brasil e o segundo em soluções de atrazine, sulfentrazone e água. Quatro aplicações de herbicidas foram realizadas via irrigação. Foram determinados a massa seca total das plantas, colonização micorrízica, número de esporos, respiração basal do solo rizosférico e taxa de sobrevivência de plantas bioindicadoras após fitorremediação. Trichilia hirta apresentou maior biomassa quando tratada com atrazina e sulfentrazone. Os herbicidas diminuíram a atividade microbiana em Triplaris americana e não afetaram os indicadores microbiológicos de Myrsine gardneriana, Schizolobium parahyba e Toona ciliata. Menos plantas bioindicadoras sobreviveram no solo com Triplaris americana e sulfentrazone. Os indicadores microbiológicos foram influenciados de formas distintas entre as espécies pela presença dos herbicidas na rizosfera.

Effects of nitrogen and phosphorus availability on the early growth of two congeneric pairs of savanna and forest species / Efeitos da disponibilidade de nitrogênio e fósforo no crescimento inicial de dois pares congenéricos de espécies de savana e floresta

In the tropical region, savannas and seasonal forests, both highly diverse biomes, occur side by side, under the same climate. If so, that mosaic cannot be explained solely by climatic variables, but also by fire, water availability and soil status. Nutrient availability in the soil, especially nitrogen and phosphorus, has been postulated to explain the abrupt transitions between savannas and seasonal forests in tropical regions. Plants from these two biomes may present different nutritional strategies to cope with nitrogen and phosphorus limitation. We used two congeneric pairs of trees — each pair with a species from the savanna and another from the neighboring seasonal forest — to test whether savanna and forest species presented different nutritional strategies during their early development. We cultivated 56 individuals from each of these species in a hydroponics system with four treatments: (1) complete Hoagland solution, (2) Hoagland solution without nitrogen, (3) Hoagland solution without phosphorus, and (4) Hoagland solution without nitrogen and phosphorus. After 45 days, we harvested the plants and measured total biomass, root to shoot ratio, height, leaf area, and specific leaf area. Overall, savanna species were lighter, shorter, with smaller leaves, higher specific leaf areas, and higher root to shoot ratios when compared to the forest species. Nitrogen increased the performance of species from both biomes. Phosphorus improved the performance of the forest species and caused toxicity symptoms in the savanna species. Hence, savanna and forest species presented different demands and were partially distinct already as seedlings concerning their nutritional strategies.

Em regiões tropicais, savanas e florestas estacionais, biomas altamente diversos, ocorrem lado a lado, sob o mesmo clima. Sendo assim, esse mosaico não pode ser explicado somente por variáveis climáticas, devendo ser considerada a frequência e intensidade de incêndios, disponibilidade de água e status do solo. A disponibilidade de nutrientes no solo, especialmente nitrogênio e fósforo, tem sido postulada para explicar as transições abruptas entre savanas e florestas estacionais nos trópicos. Espécies vegetais desses dois biomas podem apresentar estratégias nutricionais diferentes para lidar com a limitação tanto de nitrogênio como de fósforo. Utilizamos dois pares de árvores congenéricas — cada par com uma espécie típica de savana e outra de floresta estacional vizinha — para testar se as espécies da savana e da floresta apresentaram estratégias nutricionais diferentes durante seu desenvolvimento inicial. Cultivamos 56 indivíduos de cada uma dessas espécies em um sistema hidropônico com quatro tratamentos: (1) solução Hoagland completa, (2) solução Hoagland sem nitrogênio, (3) solução Hoagland sem fósforo e (4) solução Hoagland sem nitrogênio e fósforo. Após 45 dias, colhemos as plantas e medimos a biomassa total, a relação raiz / parte aérea, altura, área foliar e área foliar específica. No geral, as espécies savânicas foram mais leves, menores em altura, área foliar e área foliar específica e apresentaram maiores razões entre biomassa radicular por biomassa aérea quando comparadas às espécies florestais. A oferta de nitrogênio aumentou o desempenho das espécies de ambos biomas. O fósforo melhorou o desempenho das espécies florestais e causou sintomas de toxicidade nas espécies savânicas. Concluímos que, já como mudas, espécies congenéricas de savana e floresta apresentaram demandas distintas e foram parcialmente diferentes em relação a suas estratégias nutricionais.

Uncovering the multi-level response of Glycine max L. to the application of allelopathic biostimulant from Levisticum officinale Koch.

The interest expressed by the agriculture in the category of innovative biostimulants is due to the intensive search for natural preparations. Our study is the first ever to report a complex approach to the use of allelopathic extracts from Levisticum officinale Koch. roots in soybean cultivation, includes analyses of morphological observations, and analyses of biochemical indicators. Hot method of aqueous extraction was applied. The extracts were administered via foliar application and soil treatment. Lovage extracts had high contents of polyphenolic compounds and rich micro- and macroelemental composition. The infusions did not contain gibberellic acid and indole-3-acetic acid but the abscisic acid and saccharose, glucose, and fructose were found. The extracts modified soybean plant physiology, as manifested by changes in biometric traits. Plants responded positively by increased yield. Seeds from the treated plants had higher contents of micro- and macroelements, as well as total concentrations of lipids (with a slight decrease in protein content). In addition, they featured changes in their amino acid profile and fatty acid composition. The application of allelopathic biostimulant caused increased concentrations of isoflavones and saponins. The natural biostimulants from Levisticum officinale may become a valuable tool in the sustainable agriculture.

Negative effects of nitrogen override positive effects of phosphorus on grassland legumes worldwide.

Anthropogenic nutrient enrichment is driving global biodiversity decline and modifying ecosystem functions. Theory suggests that plant functional types that fix atmospheric nitrogen have a competitive advantage in nitrogen-poor soils, but lose this advantage with increasing nitrogen supply. By contrast, the addition of phosphorus, potassium, and other nutrients may benefit such species in low-nutrient environments by enhancing their nitrogen-fixing capacity. We present a global-scale experiment confirming these predictions for nitrogen-fixing legumes (Fabaceae) across 45 grasslands on six continents. Nitrogen addition reduced legume cover, richness, and biomass, particularly in nitrogen-poor soils, while cover of non-nitrogen-fixing plants increased. The addition of phosphorous, potassium, and other nutrients enhanced legume abundance, but did not mitigate the negative effects of nitrogen addition. Increasing nitrogen supply thus has the potential to decrease the diversity and abundance of grassland legumes worldwide regardless of the availability of other nutrients, with consequences for biodiversity, food webs, ecosystem resilience, and genetic improvement of protein-rich agricultural plant species.

Genetic transformation of legumes: an update.

KEY MESSAGE: This review summarizes the recent advances in legume genetic transformation and provides an insight into the critical factors that play a major role in the process. It also sheds light on some of the potential areas which may ameliorate the transformation of legumes. Legumes are an important group of dicotyledonous plants, highly enriched in proteins and minerals. Majority of the legume plants are cultivated in the arid and semi-arid parts of the world, and hence said to be climate resilient. They have the capability of atmospheric nitrogen fixation and thus play a vital role in the ecological sphere. However, the worldwide production of legumes is somehow not up to the mark and the yields are greatly affected by various biotic and abiotic stress factors. Genetic engineering strategies have emerged as a core of plant biology and remarkably facilitate the crop improvement programmes. A significant progress has been made towards the optimization of efficient transformation system for legume plants over the years but this group is still underutilized in comparison to other crops. Among the variety of available DNA delivery systems, Agrobacterium-mediated and particle bombardment have been primarily deployed for optimization and trait improvement. However, recalcitrance and genotype-dependence are some of the major bottlenecks for successful transformation. In this context, the present review summarizes the advances taken place in the area of legume transformation and provides an insight into the present scenario. The challenges and future possibilities for yield improvement have also been discussed.

Response to Salinity in Legume Species: An Insight on the Effects of Salt Stress during Seed Germination and Seedling Growth.

The process of soil salinization and the preponderance of saline water sources all over the world represent one of the most harmful abiotic stress to plant growth. This pointed to the importance of obtaining plants which are tolerant or resistant to salt, considering that projection of climate change for the coming years indicate an increase in temperature and rain scarcity. In the current study, the effect of NaCl was investigated on germinating seeds of Lathyrus sativus L., Vicia sativa L., Vigna radiata L. R.Wilczek and Vigna unguiculata L. Walp., by combining physiological, biochemical, biostatistical and ultrastructural analyses. Our results revealed that germination was not influenced by high NaCl concentrations, while seedling growth was affected even at low NaCl concentrations, probably due to an alteration in water uptake and in organic matter biosynthesis. Nevertheless, the synthesis of antioxidant enzymes, phenolic acids and flavonoids was registered in all species, which tended to cope with the increasing salt stress, allowing a response mechanism such as cytoplasm detoxification and cellular turgor maintenance. Besides, the ultrastructural analysis evidenced plasmolyzed cells close to cells with a normal ultrastructure with no appreciable differences among the species. This research deeply investigates the mechanism of salt-stress response focusing on species never tested before for their possible tolerance to salinity.

Salicylic acid and H2O2 seed priming alleviates Fe deficiency through the modulation of growth, root acidification capacity and photosynthetic performance in Sulla carnosa.

Iron (Fe) is one of the essential nutrients for plant growth which is involved in several physiological functions. Hence, there are intensive efforts to improve plant tolerance to Fe deficiency, by genotypic screening and by the use of adapted physiological tools. The intend of the current study was to explore the seed priming effect with salicylic acid (SA 0.25 mM) and hydrogen peroxide (H2O2 20 mM), either separately applied or combined, on plant growth, nutritional elements status (Fe and potassium K), root acidification and photosynthetic activity in two S. carnosa cultivars (Sidi Khlif and Kalbia) with different tolerance to such constraint. Under unprimed conditions, Fe deficiency decreased plant growth, chlorophyll concentration, in addition to Fe and K contents. Moreover, it affected the photosynthetic activity by inhibiting the net CO2 assimilation rate and increasing the transpiration rate of both cultivars, following a reduced water use efficiency. The changes above described were much less pronounced in Sidi Khlif than in Kalbia. The stomatal conductance increased in Fe-deficient leaves of both cultivars, suggesting that the photosynthesis impairment should be attributed to non-stomatal factors. Interestingly, priming seeds with both agents significantly improved the growth performance and the rhizosphere acidification of deficient S. carnosa plants. However, the D + SA + H2O2 treatment had the most beneficial effect on S. carnosa plant growth. The degree of this stimulation may vary depending on the cultivar, the tissue and the priming agent applied. This could be owing to the photosynthetic performance modulation, leading to more efficient nutrient uptake.

Biochemical and economical effect of application biostimulants containing seaweed extracts and amino acids as an element of agroecological management of bean cultivation.

The implementation of agronomic activities, based on the use of biostimulants, is an important element of agroecological practices. Therefore, comprehensive research was carried on the use of biostimulants. A field experiment was performed in 2016-2018 with common bean of Mexican Black cultivar. In particular growing seasons, bean plants were treated with Kelpak SL (seaweed extracts) and Terra Sorb Complex (free amino acids) in the form of single and double spraying with two solutions concentrations. According to the obtained data, application of biostimulants increased the yield of bean. Better results were observed after the use of Kelpak SL. The application of preparations influenced nutritional and nutraceutical quality of bean seeds. Terra Sorb Complex caused the highest increase in proteins level. In the light of achieved data, biostimulants in similar level decreased the starch accumulation. The most promising results, in the context of nutraceutical value of bean, were obtained in the case of increasing level of fiber. A positive impact of biostimulants on the seeds antioxidant potential was noted, expressed by the increased synthesis of phenolics, flavonoid, anthocyanins and antioxidant activities. Results of this study, directly indicate economic benefits from the use of biostimulants, which are extremely important to the farmers.

Transcriptome Analysis Reveals Potential Roles of Abscisic Acid and Polyphenols in Adaptation of Onobrychis viciifolia to Extreme Environmental Conditions in the Qinghai-Tibetan Plateau.

A detailed understanding of the molecular mechanisms of plant stress resistance in the face of ever-changing environmental stimuli will be helpful for promoting the growth and production of crop and forage plants. Investigations of plant responses to various single abiotic or biotic factors, or combined stresses, have been extensively reported. However, the molecular mechanisms of plants in responses to environmental stresses under natural conditions are not clearly understood. In this study, we carried out a transcriptome analysis using RNA-sequencing to decipher the underlying molecular mechanisms of Onobrychis viciifolia responding and adapting to the extreme natural environment in the Qinghai-Tibetan Plateau (QTP). The transcriptome data of plant samples collected from two different altitudes revealed a total of 8212 differentially expressed genes (DEGs), including 5387 up-regulated and 2825 down-regulated genes. Detailed analysis of the identified DEGs uncovered that up-regulation of genes potentially leading to changes in hormone homeostasis and signaling, particularly abscisic acid-related ones, and enhanced biosynthesis of polyphenols play vital roles in the adaptive processes of O. viciifolia. Interestingly, several DEGs encoding uridine diphosphate glycosyltransferases, which putatively regulate phytohormone homeostasis to resist environmental stresses, were also discovered. Furthermore, numerous DEGs encoding transcriptional factors, such as members of the myeloblastosis (MYB), homeodomain-leucine zipper (HD-ZIP), WRKY, and nam-ataf1,2-cuc2 (NAC) families, might be involved in the adaptive responses of O. viciifolia to the extreme natural environmental conditions. The DEGs identified in this study represent candidate targets for improving environmental stress resistance of O. viciifolia grown in higher altitudes of the QTP, and can provide deep insights into the molecular mechanisms underlying the responses of this plant species to the extreme natural environmental conditions of the QTP.

Cloning and functional analysis of AmDUF1517 promoter from Ammopiptanthus mongolicus.

Domains of unknown function protein family 1517 (DUF1517) in Ammopiptanthus mongolicus, could be induced by abiotic stresses, whose upstream regulatory sequence might be an ideal source of abiotic-induced promoter. In this study, a 1026-bp promoter of AmDUF1517 from A. mongolicus was cloned. Five deletion fragments (Full, Q1-Q4) of different length of the AmDUF1517 promoter were fused with the ß-glucuronidase (GUS) reporter and transformed into Arabidopsis thaliana. The deletion analysis showed that sequences Full, Q1 and Q3 responded well to mannitol, NaCl and 4 °C stresses, while Q2 and Q4 segments did not. The Q3 fragment (280 bp; -280 to -1 bp) showed the highest promoter activity under normal and mannitol, NaCl and 4 °C conditions. The result suggested that Q3 in the AmDUF1517 gene promoter could be a new source of induced promoters for abiotic resistance breeding in plant genetic engineering.

Zinc toxicity in seedlings of three trees from the Fabaceae associated with arbuscular mycorrhizal fungi.

Due to diverse human activities zinc (Zn) may reach phytotoxic levels in the soil. Here, we evaluated the differential sensibility of three Brazilian tree species from the Fabaceae to increasing soil Zn concentrations and its physiological response to cope with excess Zn. A greenhouse experiment was conducted with the species: Mimosa caesalpiniaefolia, Erythrina speciosa and Schizolobium parahyba, and the addition of 0, 200, 400 and 600 mg Zn kg-1 to the soil. Plants were harvested after three months of cultivation, and growth, root symbiosis, biochemical markers and elemental composition were analyzed. Soil Zn addition reduced seedling growth, irrespective of the species, with a strong reduction in M. caesalpiniaefolia. Regarding root symbiosis, in N2-fixing species, nitrogenase activity was reduced by the highest Zn concentrations. Zn addition caused plants nutritional imbalances, mainly in roots. The content of photosynthetic pigments in leaves decreased up to 40%, suggesting that high Zn contents interfered with its biosynthesis, and altered the content of foliar polyamines and free amino acids, depending on the species and the soil Zn concentration. Zn toxicity in M. caesalpiniaefolia plants was observed at available soil Zn concentrations greater than 100 mg kg-1 (DTPA-extractable), being the most sensitive species and E. speciosa was moderately sensitive. S. parahyba was a moderately tolerant species, which seems to be related to polyamines accumulation and to mycorrhizal association. This last species has the potential for revegetation of areas with moderately high soil Zn concentration and for phytostabilization purposes. Future research evaluating the tolerance to multiple metal stress under field conditions should confirm S. parayba suitability in Zn contaminated areas of tropical regions.

Evaluation of effects of Poincianella bracteosa (Tul.) L.P. Queiroz leaves in Allium cepa and Mus musculus.

POINCIANELLA BRACTEOSA: (Tul.) L.P. Queiroz. (Fabaceae) traditionally is used in Brazilian medicine to treat catarrhal infections, diarrhea, hepatitis and anemia. We investigated the phytochemical profile, and mutagenicity and anti-mutagenicity of aqueous extracts of leaves of P. bracteosa in A. cepa cells and in mice. We investigated four concentrations of extract for the A. cepa bioassay and three doses of extract for administration to mice. For the A. cepa assay, we analyzed 5,000 meristematic cells to determine the mitotic index, mean number of chromosome alterations and percentage of damage reduction. For each animal assay, 2,000 normochromatic erythrocytes were evaluated per mouse to determine the number of micronuclei and the protective effect of the extract. Phytochemical analysis of the extract revealed reducing sugars, tannins and alkaloids, which likely did not interfere with the cell cycle of A. cepa or cause damage to the DNA of A. cepa or mice. The extract exhibited a protective effect in both organisms.

Effects of saponin capped triangular silver nanocrystals on the germination of Pisum sativum, Cicer arietinum, Vigna radiata seeds & their subsequent growth study.

In this study, saponin capped triangular silver nanocrystals have been synthesised using fenugreek seed extract, where the extract acts both as a reducing and capping agent. X-ray diffraction study confirms the purity and crystalline nature of the prepared nanocrystals and transmission electron microscopic study shows the triangular morphology with the average edge length of 72 nm, along with the atomic force microscopy study for the height or the width of the triangular nanocrystals. These nanocrystals have been investigated against a few pulses (seeds) such as Pisum sativum, Cicer arietinum and Vigna radiata for their effect on the germination as well as growth of root and shoot. Considering different concentration of silver nanocrystals solution, it has been found that 25 × 10-4 and 80 × 10-4 µg/ml are the minimum and maximum concentrations of silver nanocrystals, within this range, germination and subsequent growth of root and shoot are effective. The result shows significant positive influence on the growth of root and shoot of all seeds in comparison to those of unexposed control germination. Therefore, the result of this experiment has confirmed that the use of saponin capped silver nanocrystals enhances the germination and growth of plants.

Mimosine facilitates metallic cation uptake by plants through formation of mimosine-cation complexes.

KEY MESSAGE: Iron deficiency conditions as well as iron supplied as a Fe(III)-mimosine complex induced a number of strategy I and strategy II genes for iron uptake in leucaena. Leucaena leucocephala (leucaena) is a tree-legume that can grow in alkaline soils, where metal-cofactors like Fe(III) are sparingly available. Mimosine, a known chelator of Fe(III), may facilitate Fe(III) uptake in leucaena by serving as a phytosiderophore. To test if mimosine can serve as a phytosiderophore, three sets of experiments were carried out. First, the binding properties and solubility of metal-mimosine complexes were assessed through spectrophotometry. Second, to study mimosine uptake in plants, pole bean, common bean, and tomato plants were supplied with mimosine alone and metal-mimosine complexes. Third, the expression of strategy I (S1) and strategy II (S2) genes for iron uptake from the soil was studied in leucaena plants exposed to different Fe(III) complexes. The results of this study show that (i) mimosine has high binding affinity for metallic cations at alkaline pH, Fe(III)-mimosine complexes are water soluble at alkaline pH, and that mimosine can bind soil iron under alkaline pH; (ii) pole bean, common bean, and tomato plants can uptake mimosine and transport it throughout the plant; and (iii) a number of S1 and S2 genes were upregulated in leucaena under iron-deficiency condition or when Fe(III) was supplied as a Fe(III)-mimosine complex. These findings suggest that leucaena may utilize both S1 and S2 strategies for iron uptake; and mimosine may play an important role in both strategies.

Silver nanoparticles (AgNPs) induced impairment of in vitro pollen performance of Peltophorum pterocarpum (DC.) K. Heyne.

Increasing use of silver nanoparticles (AgNPs) in myriad applications including electronics, medicines and agriculture has led to serious concerns regarding its release to plant ecosystems. Over the years, numerous studies have demonstrated the toxic impact of AgNPs in a variety of cell and tissue systems involved in vegetative growth across a wide range of plant species. However, assessing their impact on haploid phase of plant life cycle was restricted only to a study with Kiwifruit. In this study, in vitro pollen performance of Peltophorum pterocarpum at two endpoints i.e., germination and tube growth was assessed to evaluate the impact of nanoparticulate or ionic form of silver. Increasing concentrations of AgNO3/AgNPs significantly reduced the pollen germination and retarded the tube growth. The EC 50 values indicated a more potent toxic effect of AgNPs than AgNO3 on pollen germination as well as tube growth. Impairment of pollen performance was more pronounced at the stage of emergence of pollen tube. Extensive alterations in the muri and lumen of exine as revealed through SEM analysis and subsequent blockage of germpore might disrupt the emergence of pollen tube. The dynamics of pollen tube growth was analyzed with polynomial models of different degrees. A high degree of polynomial, the quintic model was able to approximate the real data points with highest coefficient of determination and smallest RMSE, compared to other models. An oscillating pattern of tube growth was portrayed with the passage of time in all the treatments that fits well with the established mechanistic oscillatory model of tube growth. It appears that exposure to AgNO3/AgNPs inhibited pollen germination and retarded tube growth without affecting the oscillatory behavior of tip-growth.

Glutathione is Involved in Detoxification of Peroxide and Root Nodule Symbiosis of Mesorhizobium huakuii.

Legumes interact with symbiotic rhizobia to produce nitrogen-fixation root nodules under nitrogen-limiting conditions. The contribution of glutathione (GSH) to this symbiosis and anti-oxidative damage was investigated using the M. huakuii gshB (encoding GSH synthetase) mutant. The gshB mutant grew poorly with different monosaccharides, including glucose, sucrose, fructose, maltose, or mannitol, as sole sources of carbon. The antioxidative capacity of gshB mutant was significantly decreased by these treatments with H2O2 under the lower concentrations and cumene hydroperoxide (CUOOH) under the higher concentrations, indicating that GSH plays different roles in response to organic peroxide and inorganic peroxide. The gshB mutant strain displayed no difference in catalase activity, but significantly lower levels of the peroxidase activity and the glutathione reductase activity than the wild type. The same level of catalase activity could be associated with upregulation of the transcriptional activity of the catalase genes under H2O2-induced conditions. The nodules infected by the gshB mutant were severely impaired in abnormal nodules, and showed a nodulation phenotype coupled to a 60% reduction in the nitrogen fixation capacity. A 20-fold decrease in the expression of two nitrogenase genes, nifH and nifD, is observed in the nodules induced by gshB mutant strain. The symbiotic deficiencies were linked to bacteroid early senescence.

Effect of lead on the physiological, biochemical and ultrastructural properties of Leucaena leucocephala.

Heavy metals are characterised by a relatively high density and cause genotoxic, cytotoxic and mutagenic effects on plants, animals and humans. Lead (Pb) is one of the heavy metals that causes toxicity to plants and animals. This experiment was conducted using a hydroponic technique to study the effects of Pb(NO3 )2 on physiological, biochemical and ultrastructural characteristics in Leucaena leucocephala seedlings. Plants were grown in a growth chamber for 21 days in Hoagland's solution supplemented with 0 (control), 25, 50, 100, 300, 500 and 700 µm Pb(NO3 )2 . Shoot heights as well as root lengths decreased significantly in Pb-treated plants with 300, 500 and 700 µm. In Pb-treated plants with high Pb concentrations, photosynthesis rate (PN ), stomatal conductance (gs ) and transpiration rate (E) decreased. Total protein and carbohydrate content in Pb-treated plants with 300, 500 and 700 µm increased significantly in leaves. Moreover, in Pb-treated plants with 300, 500 and 700 µm Pb(NO3 )2 , mesophyll cells had enlarged chloroplasts with disrupted thylakoid membranes associated with large starch grains. In contrast, Pb treatments with 25, 50 µm and 100 µm were not toxic to the plants. Thick sections of roots of Pb-treated plants with 300, 500 and 700 µm Pb showed distinct changes in structure of epidermal and cortical cells. Moreover, thin sections of roots of Pb-treated plants with 300, 500 and 700 µm Pb had thickened walls of xylem cells. These results will shed more light in understanding the effects of heavy metal stress on plants.

Methyl jasmonate and cyclodextrin-mediated defense mechanism and protective effect in response to paraquat-induced stress in peanut hairy root.

Plant cells have a variety of defense mechanisms to alleviate the deleterious effects of oxidative stress. The present work elucidated a schematic diagram of the proposed pathway of peanut hairy root tissue treated with different elicitors; paraquat (PQ), methyl jasmonate (MeJA), and cyclodextrin (CD). The different elicitation approaches could provoke intrinsic stress in plant cells and might activate a distinct response pathway, allowing plants to overcome the deleterious effects of oxidative stress. Among all strategies, hairy root culture pretreated with PQ followed by application of MeJA plus CD showed an extensive induction of antioxidant defense mechanisms. The expression of the antioxidant enzyme genes and stilbene-synthesized enzyme genes were up-regulated in accordance with the dramatic increase in the production of stilbene compounds. The non-enzymatic antioxidant substances exhibited a highly enhanced capability. The pathogenesis-related protein (PR) genes were also highly up-regulated. In summary, we demonstrated that the interplay among MeJA plus CD and PQ may activate a complex signaling network to regulate plant defense mechanisms involving the up-regulation of detoxifying enzymes, induction of free-radical scavengers and overexpression of genes associated with plant defense pathways.

The role of gibberellic acid and zinc sulfate on biochemical performance relate to drought tolerance of white bean under water stress.

In this study the effects of zinc sulfate and gibberellin on agro physiological of white bean under water deficiency were studied. Therefore, an experiment was conducted in a split-split plot design based on a randomized complete block with three replications in two places. The experimental factors included three irrigation levels, spraying of zinc sulfate in four levels and two levels of non-spraying and spraying of gibberellin. Analysis of measured data indicated that the water stress had a significant effect on all traits, except proline amount and 100 seeds weight. Spraying of zinc sulfate showed a significant effect on all traits except carotenoid value. Application of gibberellin had a significant effect on all traits except ion leakage, carotenoids, number of seeds per pod and grain yield. The interaction effect of stress×zincsulfate×gibberellin was significant on all traits except number of seeds per pod. In addition, comparison of means at 5% level, showed that application of 1.5 ml L-1of zinc sulfate plus gibberellin improved bean biochemical properties. Under optimum water level, using of 4.5 ml L-1of zinc sulfate and under severe water stress conditions, using of 4.5 ml L-1 of zinc sulfate plus gibberellin are recommended for obtaining the maximum crop performance.