RESUMEN
Potatoes are one of the main sources of carbohydrates in human diet, however they have a high glycaemic index (GI). Hence, developing new agricultural and industrial strategies to produce low GI potatoes represents a health priority to prevent obesity and related diseases. In this work, we investigated whether treatments of potato plants with elicitors of plant defence responses can lead to a reduction of tuber starch availability and digestibility, through the induction of cell wall remodelling and stiffening. Treatments with phosphites (KPhi) and borate were performed, as they are known to activate plant defence responses that cause modifications in the architecture and composition of the plant cell wall. Data of suberin autofluorescence demonstrated that potato plants grown in a nutrition medium supplemented with KPhi and borate produced tubers with a thicker periderm, while pectin staining demonstrated that KPhi treatment induced a reinforcement of the wall of storage parenchyma cells. Both compounds elicited the production of H2O2, which is usually involved in cell-wall remodelling and stiffening reactions while only KPhi caused an increase of the total content of phenolic compounds. A two-phase digestion in vitro assay showed that treatment with KPhi determined a significant decrease of the starch hydrolysis rate in potato tubers. This work highlights the ability of cell wall architecture in modulating starch accessibility to digestive enzymes, paving the way for new agronomic practices to produce low GI index potatoes.
Asunto(s)
Boratos/farmacología , Pared Celular/ultraestructura , Fosfitos/farmacología , Tubérculos de la Planta/efectos de los fármacos , Compuestos de Potasio/farmacología , Solanum tuberosum/efectos de los fármacos , Almidón/metabolismo , Digestión , Flavonoides/metabolismo , Índice Glucémico , Peróxido de Hidrógeno/metabolismo , Hidroxibenzoatos/metabolismo , Técnicas In Vitro , Células del Mesófilo/efectos de los fármacos , Células del Mesófilo/ultraestructura , Tubérculos de la Planta/química , Tubérculos de la Planta/metabolismo , Tubérculos de la Planta/ultraestructura , Solanum tuberosum/química , Solanum tuberosum/metabolismo , Solanum tuberosum/ultraestructuraRESUMEN
KEY MESSAGE: We describe two types of plastid outgrowths visualised in potato tubers after carboxyfluorescein diacetate staining. Probable esterase activity of the outgrowths has been demonstrated for the first time ever. Plastid outgrowths were observed in the phelloderm and storage parenchyma cells of red potato (S. tuberosum L. cv. Rosalinde) tubers after administration of carboxyfluorescein diacetate stain. Endogenous esterases cleaved off acetic groups to release membrane-unpermeable green fluorescing carboxyfluorescein which accumulated differentially in particular cell compartments. The intensive green fluorescence of carboxyfluorescein exhibited highly branched stromules (stroma-filled plastid tubular projections of the plastid envelope) and allowed distinguishing them within cytoplasmic strands of the phelloderm cells. Stromules (1) were directed towards the nucleus or (2) penetrated the whole cells through the cytoplasmic bands of highly vacuolated phelloderm cells. Those directed towards the nucleus were flattened and adhered to the nuclear envelope. Stromule-like interconnections between two parts of the same plastids (isthmuses) were also observed. We also documented the formation of another type of the stroma-filled plastid outgrowths, referred to here as protrusions, which differed from previously defined stromules in both morphology and esterase activity. Unlike stromules, the protrusions were found to be associated with developmental processes leading to starch accumulation in the storage parenchyma cells. These results strongly suggest that stromules and protrusions exhibit esterase activity. This has been demonstrated for the first time. Morphological and biochemical features as well as possible functions of stromules and protrusions are discussed below.
Asunto(s)
Fluoresceínas , Colorantes Fluorescentes , Tubérculos de la Planta/ultraestructura , Plastidios/ultraestructura , Solanum tuberosum/ultraestructura , Núcleo Celular/metabolismo , Núcleo Celular/ultraestructura , Citoplasma/metabolismo , Citoplasma/ultraestructura , Tubérculos de la Planta/metabolismo , Plastidios/metabolismo , Solanum tuberosum/crecimiento & desarrollo , Coloración y EtiquetadoRESUMEN
The edible tubers from different species of Dioscorea are a major source of food and nutrition for millions of people. Some of the species are medicinally important but others are toxic. The genus consists of about 630 species of almost wholly dioecious plants, many of them poorly characterized. The taxonomy of Dioscorea is confusing and identification of the species is generally problematic. There are no adequate anatomical studies available for most of the species. This study is aimed to fill this gap and provides a detailed investigation of the anatomy and micro-morphology of the rhizomes and tubers of five different species of Dioscorea, namely D. balcanica, D. bulbifera, D. polystachya, D. rotundata and D. villosa. The primary features that can help in distinguishing the species include the nature of periderm, presence or absence of pericyclic sclereids, lignification in the phloem, types of calcium oxalate crystals and features of starch grains. The descriptions are supported with images of bright-field and scanning electron microscopy for better understanding of these species. The diagnostic key of anatomical features included in this paper can help distinguish the investigated species unambiguously. Additionally, HPTLC analyses of authentic and commercial samples of the five species are described.
Asunto(s)
Dioscorea/anatomía & histología , Dioscorea/química , Cromatografía en Capa Delgada , Dioscorea/clasificación , Dioscorea/ultraestructura , Tubérculos de la Planta/anatomía & histología , Tubérculos de la Planta/química , Tubérculos de la Planta/clasificación , Tubérculos de la Planta/ultraestructuraRESUMEN
Following tuber induction, potato tubers undergo a period of dormancy during which visible bud growth is inhibited. The length of the dormancy period is under environmental, physiological and hormonal control. Sucrose availability is one prerequisite for bud break. In the absence of sucrose, no bud break occurs. Thus, sucrose is likely to serve as nutrient and signal molecule at the same time. The mode of sucrose sensing is only vaguely understood, but most likely involves trehalose-6-phosphate and SnRK1 signalling networks. This conclusion is supported by the observation that ectopically manipulation of trehalose-6-phosphate levels influences the length of the dormancy period. Once physiological competence is achieved, sprouting is controlled by the level of phytohormones. Two phytohormones, ABA and ethylene, are supposed to suppress tuber sprouting; however, the exact role of ethylene remains to be elucidated. Cytokinins and gibberellins are required for bud break and sprout growth, respectively. The fifth classical phytohormone, auxin, seems to play a role in vascular development. During the dormancy period, buds are symplastically isolated, which changes during bud break. In parallel to the establishment of symplastic connectivity, vascular tissue develops below the growing bud most likely to support the outgrowing sprout with assimilates mobilised in parenchyma cells. Sprouting leads to major quality losses of stored potato tubers. Therefore, control of tuber sprouting is a major objective in potato breeding. Although comparative transcriptome analysis revealed a large number of genes differentially expressed in growing versus dormant buds, no master-regulator of potato tuber sprouting has been identified so far.
Asunto(s)
Tubérculos de la Planta/crecimiento & desarrollo , Solanum tuberosum/fisiología , Citocininas/metabolismo , Ambiente , Regulación de la Expresión Génica de las Plantas , Giberelinas/metabolismo , Ácidos Indolacéticos/metabolismo , Reguladores del Crecimiento de las Plantas/metabolismo , Tubérculos de la Planta/ultraestructura , Solanum tuberosum/crecimiento & desarrollo , Sacarosa/metabolismo , Fosfatos de Azúcar , Trehalosa/análogos & derivadosRESUMEN
Parenchyma cells from tubers of Solanum tuberosum L. convert several externally supplied sugars to starch but the rates vary largely. Conversion of glucose 1-phosphate to starch is exceptionally efficient. In this communication, tuber slices were incubated with either of four solutions containing equimolar [U-¹4C]glucose 1-phosphate, [U-¹4C]sucrose, [U-¹4C]glucose 1-phosphate plus unlabelled equimolar sucrose or [U-¹4C]sucrose plus unlabelled equimolar glucose 1-phosphate. C¹4-incorporation into starch was monitored. In slices from freshly harvested tubers each unlabelled compound strongly enhanced ¹4C incorporation into starch indicating closely interacting paths of starch biosynthesis. However, enhancement disappeared when the tubers were stored. The two paths (and, consequently, the mutual enhancement effect) differ in temperature dependence. At lower temperatures, the glucose 1-phosphate-dependent path is functional, reaching maximal activity at approximately 20 °C but the flux of the sucrose-dependent route strongly increases above 20 °C. Results are confirmed by in vitro experiments using [U-¹4C]glucose 1-phosphate or adenosine-[U-¹4C]glucose and by quantitative zymograms of starch synthase or phosphorylase activity. In mutants almost completely lacking the plastidial phosphorylase isozyme(s), the glucose 1-phosphate-dependent path is largely impeded. Irrespective of the size of the granules, glucose 1-phosphate-dependent incorporation per granule surface area is essentially equal. Furthermore, within the granules no preference of distinct glucosyl acceptor sites was detectable. Thus, the path is integrated into the entire granule biosynthesis. In vitro C¹4C-incorporation into starch granules mediated by the recombinant plastidial phosphorylase isozyme clearly differed from the in situ results. Taken together, the data clearly demonstrate that two closely but flexibly interacting general paths of starch biosynthesis are functional in potato tuber cells.
Asunto(s)
Ciclo del Carbono , Solanum tuberosum/citología , Solanum tuberosum/metabolismo , Almidón/metabolismo , Ciclo del Carbono/efectos de los fármacos , Isótopos de Carbono , Mezclas Complejas , Glucanos/metabolismo , Glucofosfatos/farmacología , Isoenzimas/metabolismo , Tubérculos de la Planta/citología , Tubérculos de la Planta/efectos de los fármacos , Tubérculos de la Planta/fisiología , Tubérculos de la Planta/ultraestructura , Plantas Modificadas Genéticamente , Plastidios/efectos de los fármacos , Plastidios/enzimología , Polisacáridos/metabolismo , Solanum tuberosum/genética , Solanum tuberosum/fisiología , Solubilidad/efectos de los fármacos , Almidón/ultraestructura , Almidón Fosforilasa/metabolismo , Almidón Sintasa/metabolismo , Sacarosa/farmacología , TemperaturaRESUMEN
Potato (Solanum tuberosum) tuber, a swollen underground stem, is used as a model system for the study of dormancy release and sprouting. Natural dormancy release, at room temperature, is initiated by tuber apical bud meristem (TAB-meristem) sprouting characterized by apical dominance (AD). Dormancy is shortened by treatments such as bromoethane (BE), which mimics the phenotype of dormancy release in cold storage by inducing early sprouting of several buds simultaneously. We studied the mechanisms governing TAB-meristem dominance release. TAB-meristem decapitation resulted in the development of increasing numbers of axillary buds with time in storage, suggesting the need for autonomous dormancy release of each bud prior to control by the apical bud. Hallmarks of programmed cell death (PCD) were identified in the TAB-meristems during normal growth, and these were more extensive when AD was lost following either extended cold storage or BE treatment. Hallmarks included DNA fragmentation, induced gene expression of vacuolar processing enzyme1 (VPE1), and elevated VPE activity. VPE1 protein was semipurified from BE-treated apical buds, and its endogenous activity was fully inhibited by a cysteinyl aspartate-specific protease-1-specific inhibitor N-Acetyl-Tyr-Val-Ala-Asp-CHO (Ac-YVAD-CHO). Transmission electron microscopy further revealed PCD-related structural alterations in the TAB-meristem of BE-treated tubers: a knob-like body in the vacuole, development of cytoplasmic vesicles, and budding-like nuclear segmentations. Treatment of tubers with BE and then VPE inhibitor induced faster growth and recovered AD in detached and nondetached apical buds, respectively. We hypothesize that PCD occurrence is associated with the weakening of tuber AD, allowing early sprouting of mature lateral buds.
Asunto(s)
Apoptosis , Flores/citología , Meristema/citología , Tubérculos de la Planta/citología , Tubérculos de la Planta/crecimiento & desarrollo , Solanum tuberosum/citología , Solanum tuberosum/crecimiento & desarrollo , Secuencia de Aminoácidos , Apoptosis/efectos de los fármacos , Núcleo Celular/efectos de los fármacos , Núcleo Celular/metabolismo , Núcleo Celular/ultraestructura , Forma del Núcleo Celular/efectos de los fármacos , Frío , Fragmentación del ADN/efectos de los fármacos , Flores/efectos de los fármacos , Flores/ultraestructura , Hidrocarburos Bromados/farmacología , Meristema/efectos de los fármacos , Meristema/metabolismo , Meristema/ultraestructura , Datos de Secuencia Molecular , Oligopéptidos/farmacología , Proteínas de Plantas/química , Proteínas de Plantas/metabolismo , Tubérculos de la Planta/efectos de los fármacos , Tubérculos de la Planta/ultraestructura , Preservación Biológica , Solanum tuberosum/efectos de los fármacos , Solanum tuberosum/ultraestructuraRESUMEN
Growth stimulation in potato Solanum tuberosum L. tubers by melafen preparation caused an increase in area ofmitochondrial apparatus (increase in mitochondrial size) in apical meristem cells. Melafen stimulated mitochondrial differentiation (increase in number of condensed mitochondria enriched in cristas). Obtained data revealed an increase in activity of mitochondrial apparatus which is connected with an increase in energetic demands of cells in potato tuber apexes at melafen growth activation.
Asunto(s)
Germinación/efectos de los fármacos , Meristema/ultraestructura , Mitocondrias , Ácidos Fosfínicos/farmacología , Tubérculos de la Planta/ultraestructura , Solanum tuberosum/ultraestructura , Triazinas/farmacología , Meristema/efectos de los fármacos , Meristema/crecimiento & desarrollo , Microscopía Electrónica , Mitocondrias/efectos de los fármacos , Mitocondrias/ultraestructura , Reguladores del Crecimiento de las Plantas/farmacología , Tubérculos de la Planta/efectos de los fármacos , Tubérculos de la Planta/crecimiento & desarrollo , Solanum tuberosum/efectos de los fármacos , Solanum tuberosum/crecimiento & desarrolloRESUMEN
A comparative ultramorphometric study of the effect of jasmonic acid (JA) on the plastid apparatus in apical cells of potato tubers varying in physiological state was performed. When tubers were treated with JA at forced rest, the plastid apparatus of apical cells decreased in area and plastid proliferation was suppressed. When treatment was performed during growth, the area of the plastid apparatus remained unchanged, division was suppressed, and plastid budding was stimulated in apical cells. There was also a common response to JA that was independent of the physiological state of tubers. JA stimulated the development of the internal membrane system in plastids, reduced the amount of protein inclusions, and increased the portion of plastids having cisterns of the granular endoplasmic reticulum (GER) around their envelopes. The ultrastructural changes in plastids made it possible to assume that JA increases the biosynthetic activity of the plastid apparatus in apical meristem cells of potato tubers.
Asunto(s)
Ciclopentanos/farmacología , Meristema/metabolismo , Oxilipinas/farmacología , Reguladores del Crecimiento de las Plantas/farmacología , Tubérculos de la Planta/metabolismo , Plastidios/metabolismo , Solanum tuberosum/metabolismo , Retículo Endoplásmico/metabolismo , Retículo Endoplásmico/ultraestructura , Meristema/ultraestructura , Proteínas de Plantas/biosíntesis , Tubérculos de la Planta/ultraestructura , Plastidios/ultraestructura , Solanum tuberosum/ultraestructuraRESUMEN
Suberin and waxes embedded in the suberin polymer are key compounds in the control of transpiration in the tuber periderm of potato (Solanum tuberosum). Suberin is a cell-wall biopolymer with aliphatic and aromatic domains. The aliphatic suberin consists of a fatty acid polyester with esterified ferulic acid, which is thought to play an important role in cross-linking to the aromatic domain. In potato, ferulic acid esters are also the main components of periderm wax. How these ferulate esters contribute to the periderm water barrier remains unknown. Here we report on a potato gene encoding a fatty omega-hydroxyacid/fatty alcohol hydroxycinnamoyl transferase (FHT), and study its molecular and physiological relevance in the tuber periderm by means of a reverse genetic approach. In FHT RNAi periderm, the suberin and its associated wax contained much smaller amounts of ferulate esters, in agreement with the in vitro ability of the FHT enzyme to conjugate ferulic acid with omega-hydroxyacid and fatty alcohols. FHT down-regulation did not affect the typical suberin lamellar ultrastructure but had significant effects on the anatomy, sealing properties and maturation of the periderm. The tuber skin became thicker and russeted, water loss was greatly increased, and maturation was prevented. FHT deficiency also induced accumulation of the hydroxycinnamic acid amides feruloyl and caffeoyl putrescine in the periderm. We discuss these results in relation to the role attributed to ferulates in suberin molecular architecture and periderm impermeability.
Asunto(s)
Aciltransferasas/metabolismo , Lípidos/biosíntesis , Proteínas de Plantas/metabolismo , Solanum tuberosum/enzimología , Ceras/metabolismo , Aciltransferasas/genética , Ácidos Cumáricos , ADN de Plantas/genética , Regulación de la Expresión Génica de las Plantas , Genes de Plantas , Filogenia , Proteínas de Plantas/genética , Tubérculos de la Planta/química , Tubérculos de la Planta/ultraestructura , Interferencia de ARN , Alineación de Secuencia , Análisis de Secuencia de ADN , Solanum tuberosum/genéticaRESUMEN
The mechanism of the stimulatory effect of melafen on potato tuber sprouting was studied. The treatment with 10(-8) M melafen intensified division and stretching and activated granular endoplasmic reticulum of apical meristem cells. An increase in the activity of membrane-bound H+-ATPase in the plasmalemma of parenchymal cells of melafen-treated potato tubers and enhancement of passive proton permeability of the plasmalemma was observed. In vitro studies showed that melafen at concentrations of 10(-5-10-12) M stimulated the activity of plasmalemmal H+-ATPase in a concentration-dependent manner.
Asunto(s)
Retículo Endoplásmico/fisiología , Ácidos Fosfínicos/farmacología , Tubérculos de la Planta/crecimiento & desarrollo , ATPasas de Translocación de Protón/fisiología , Solanum tuberosum/crecimiento & desarrollo , Triazinas/farmacología , Membrana Celular/enzimología , Membrana Celular/fisiología , Membrana Celular/ultraestructura , Permeabilidad de la Membrana Celular/efectos de los fármacos , Permeabilidad de la Membrana Celular/fisiología , Retículo Endoplásmico/efectos de los fármacos , Retículo Endoplásmico/ultraestructura , Reguladores del Crecimiento de las Plantas/farmacología , Tubérculos de la Planta/efectos de los fármacos , Tubérculos de la Planta/ultraestructura , Solanum tuberosum/efectos de los fármacos , Solanum tuberosum/ultraestructuraRESUMEN
Starch granule size is an important parameter for starch applications in industry. Starch granules are formed in amyloplasts, which are, like chloroplasts, derived from proplastids. Division processes and associated machinery are likely to be similar for all plastids. Essential roles for FtsZ proteins in plastid division in land plants have been revealed. FtsZ forms the so-called Z ring which, together with inner and outer plastid division rings, brings about constriction of the plastid. It has been shown that modulation of the expression level of FtsZ may result in altered chloroplast size and number. To test whether FtsZ is also involved in amyloplast division and whether this, in turn, may affect the starch granule size in crop plants, FtsZ protein levels were either reduced or increased in potato. As shown previously in other plant species, decreased StFtsZ1 protein levels in leaves resulted in a decrease in the number of chloroplasts in guard cells. More interestingly, plants with increased StFtsZ1 protein levels in tubers resulted in less, but larger, starch granules. This suggests that the stoichiometry between StFtsZ1 and other components of the plastid division machinery is important for its function. Starch from these tubers also had altered pasting properties and phosphate content. The importance of our results for the starch industry is discussed.
Asunto(s)
Proteínas de Plantas/genética , Plastidios/ultraestructura , Solanum tuberosum/química , Solanum tuberosum/genética , Almidón/química , Secuencia de Aminoácidos , Proteínas de Arabidopsis , Cloroplastos/metabolismo , Cloroplastos/ultraestructura , Clonación Molecular , Genes de Plantas , Datos de Secuencia Molecular , Proteínas de Plantas/química , Tubérculos de la Planta/química , Tubérculos de la Planta/genética , Tubérculos de la Planta/ultraestructura , Plantas Modificadas Genéticamente/química , Plantas Modificadas Genéticamente/genética , Plantas Modificadas Genéticamente/ultraestructura , Plastidios/química , Plastidios/metabolismo , Regiones Promotoras Genéticas , Solanum tuberosum/ultraestructura , Transformación GenéticaRESUMEN
The ultrastructure of the mitochondrial apparatus of apical tuber cells of original and transgenic (defensin gene-transfected) potato have been compared in normal and ambiol-treated plants, using morphometric approaches. No qualitative or quantitative differences were found between the mitochondria of original and transgenic plants under normal conditions (control). Treatment with ambiol produced only quantitative differences (in the number of mitochondria and their volume) between the cells of original and transgenic plants. This observation has been attributed to (1) changes in the physiology and biochemistry of transgenic plants, induced by the expression of the gene of defensin (hormonal balance, functional activity of the plasmalemmata, etc.), and (2) direct effects of ambiol.
Asunto(s)
Bencimidazoles/farmacología , Plantas Modificadas Genéticamente/efectos de los fármacos , Solanum tuberosum/efectos de los fármacos , Microscopía Electrónica , Mitocondrias/efectos de los fármacos , Mitocondrias/ultraestructura , Tubérculos de la Planta/efectos de los fármacos , Tubérculos de la Planta/ultraestructura , Plantas Modificadas Genéticamente/ultraestructura , Solanum tuberosum/genética , Solanum tuberosum/ultraestructuraRESUMEN
The major purpose of these experiments were to investigate growth of potato storage organs and starch synthesis in minitubers at slow horizontal clinorotation (2 rpm), which partly mimics microgravity, and a secondary goal was to study the activity and localization of phosphorylase (EC 2.4.1.1) in storage parenchyma under these conditions. Miniplants of Solanum tuberosum L. (cv Adreta) were grown in culture for 30 days for both the vertical control and the horizontal clinorotation. During long-term clinorotation, an acceleration of minituber formation, and an increase of amyloplast number and size in storage parenchyma cells, as well as increased starch content, was observed in the minitubers. The differences among cytochemical reaction intensity, activity of phosphorylase, and carbohydrate content in storage parenchyma cells of minitubers grown in a horizontal clinostat were established by electron-cytochemical and biochemical methods. It is shown that high phosphorylase activity is correlated with increased starch content during extended clinorotation. The results demonstrate the increase in carbohydrate metabolism and possible accelerated growth of storage organs under the influence of microgravity, as mimicked by clinorotation; therefore, clinorotation can be used as a basis for future studies on mechanisms of starch synthesis under microgravity.
Asunto(s)
Metabolismo de los Hidratos de Carbono , Fosforilasas/metabolismo , Tubérculos de la Planta/crecimiento & desarrollo , Rotación , Solanum tuberosum/crecimiento & desarrollo , Aceleración , Disacáridos/metabolismo , Estudios de Evaluación como Asunto , Microscopía Electrónica , Monosacáridos/metabolismo , Tubérculos de la Planta/enzimología , Tubérculos de la Planta/metabolismo , Tubérculos de la Planta/ultraestructura , Solanum tuberosum/enzimología , Solanum tuberosum/metabolismo , Solanum tuberosum/ultraestructura , Almidón/metabolismo , Simulación de IngravidezRESUMEN
Previous spaceflight reports attribute changes in plant ultrastructure to microgravity, but it was thought that the changes might result from growth in uncontrolled environments during spaceflight. To test this possibility, potato explants were examined (a leaf, axillary bud, and small stem segment) grown in the ASTROCULTURETM plant growth unit, which provided a controlled environment. During the 16 d flight of space shuttle Columbia (STS-73), the axillary bud of each explant developed into a mature tuber. Upon return to Earth, tuber slices were examined by transmission electron microscopy. Results showed that the cell ultrastructure of flight-grown tubers could not be distinguished from that of tuber cells grown in the same growth unit on the ground. No differences were observed in cellular features such as protein crystals, plastids with starch grains, mitochondria, rough ER, or plasmodesmata. Cell wall structure, including underlying microtubules, was typical of ground-grown plants. Because cell walls of tubers formed in space were not required to provide support against the force due to gravity, it was hypothesized that these walls might exhibit differences in wall components as compared with walls formed in Earth-grown tubers. Wall components were immunolocalized at the TEM level using monoclonal antibodies JIM 5 and JIM 7, which recognize epitopes of pectins, molecules thought to contribute to wall rigidity and cell adhesion. No difference in presence, abundance or distribution of these pectin epitopes was seen between space- and Earth-grown tubers. This evidence indicates that for the parameters studied, microgravity does not affect the cellular structure of plants grown under controlled environmental conditions.