Expression of SK3-type dehydrin in transporting organs is associated with cold acclimation in Solanum species

The expression of a gene, encoding a dehydrin protein designated as DHN24 was analyzed at the protein level in two groups of Solanum species differing in cold acclimation ability. The DHN24 protein displays consensus amino acid sequences of dehydrins, termed K- and S-segments. The S-segment precedes three K-segments, classifying the protein into SK₃-type dehydrins. A group of Solanum species able to cold acclimation constituted by S. sogarandinum and S. tuberosum, cv. Aster, and a second one composed of a S. sogarandinum line, that lost ability to cold acclimation, and of S. tuberosum, cv. Irga, displaying low ability to cold acclimation were studied. Under control conditions, noticeable levels of the DHN24 protein was observed in stems, tubers, and roots of Solanum species. No protein was detected in leaves. During low temperature treatment the DHN24 protein level substantially increased in tubers, in transporting organs and in apical parts, and only a small increase was observed in leaves. The increase in protein abundance was only observed in the plants able to cold acclimate and was found to parallel the acclimation capacity. Upon drought stress, the DHN24 level decreased in stems and in leaves, but increased in apical parts. These results suggest that Dhn24 expression is regulated by organ specific factors in the absence of stress and by factors related to cold acclimation processes during low temperature treatment in collaboration with organ-specific factors. A putative function of the SK₃-type dehydrin proteins during plant growth and in the tolerance to low temperature is discussed.     

Dehydrin and proline content in Brassica napus and B. carinata under cold stress at two irradiances

The accumulation of cold-induced dehydrin and proline was related to the frost tolerance (FT) in several Brassica species or cultivars. A dehydrin of molecular mass 47 kDa was detected in the leaves of an Ethiopian mustard (B. carinata) and a pair of dehydrins of similar molecular mass in the three (two winter, one spring) oilseed rape (B. napus) cultivars, when plants were maintained at 4 °C for one-month under two different irradiances. More dehydrin was accumulated in oilseed rape than in Ethiopian mustard under the high irradiance. A significant correlation was observed between leaf dehydrin content and FT, and no relationship between proline content and FT or between the proline and dehydrin contents. Protoplast-derived callus cells behaved differently from leaves sampled from intact plants, as they did not accumulate dehydrin and proline in response to cold stress.     

Effect of prolonged root hypoxia on the antioxidant content of tomato fruit

Tomato fruit quality depends on its metabolite content, which in turn is determined by numerous metabolic changes occurring during fruit development and ripening. The aim of this work was to investigate whether flooding affects the nutritional quality of tomato fruit, focusing on compounds essential to human health: carotenoids and ascorbate. To this end, tomato plants (Solanum lycopersicum L. cv Micro-Tom) were submitted to prolonged root hypoxia (1–2% O₂) at first flower anthesis. Fruits were harvested at five stages of the ripening process and analysed for their carotenoid and ascorbate contents. Our results showed that the ripening of fruits that developed on hypoxia treated plants was not inhibited. However, root hypoxia significantly limits carotenoid and ascorbate accumulation in pericarp during fruit ripening, the strongest effects being observed at late stages of ripening. Limitation of both carotenoids and ascorbate accumulation seems to be primarily mediated by the reduced level of expression of genes of the corresponding metabolic pathway.     

Dehydrin genes and their expression in recalcitrant oak (<Emphasis Type="Italic">Quercus robur</Emphasis>) embryos

In this work, three dehydrin genes, QrDhn1, QrDhn2, QrDhn3, were isolated from recalcitrant oak (Quercus robur). Their expression pattern was analyzed in both zygotic and somatic embryos as well as in vegetative tissues exposed to different kinds of abiotic stresses including desiccation, osmotic stress, and chilling. The QrDhn1 gene encoding for Y_nSK_n type dehydrin was expressed during later stages of zygotic embryo development but in somatic embryos only when exposed to osmotic or desiccation stress. In contrast, the other two oak dehydrin genes encoding for putative K_n type dehydrins were expressed only in somatic embryos (both not-treated and osmotically stressed) and leaves of oak seedlings exposed to desiccation. Behavior of these genes suggests that different dehydrins are involved in processes of seed maturation and response to altered osmotic (water status) conditions in somatic embryos. Revealing further members of dehydrin gene family in recalcitrant oak might contribute to clarify non-orthodox seed behavior as well as identify mechanisms contributing to desiccation tolerance in plants.     

Translocation and the alternative D-galacturonate pathway contribute to increasing the ascorbate level in ripening tomato fruits together with the D-mannose/L-galactose pathway

The D-mannose/L-galactose pathway for the biosynthesis of vitamin C (L-ascorbic acid; AsA) has greatly improved the understanding of this indispensable compound in plants, where it plays multifunctional roles. However, it is yet to be proven whether the same pathway holds for all the different organs of plants, especially the fruit-bearing plants, at different stages of development. Micro-Tom was used here to elucidate the mechanisms of AsA accumulation and regulation in tomato fruits. The mRNA expression of the genes in the D-mannose/L-galactose pathway were inversely correlated with increasing AsA content of Micro-Tom fruits during ripening. Feeding L-[6-(14)C]AsA to Micro-Tom plants revealed that the bulk of the label from AsA accumulated in the source leaf was transported to the immature green fruits, and the rate of translocation decreased as ripening progressed. L-Galactose feeding, but neither D-galacturonate nor L-gulono-1,4-lactone, enhanced the content of AsA in immature green fruit. On the other hand, L-galactose and D-galacturonate, but not L-gulono-1,4-lactone, resulted in an increase in the AsA content of red ripened fruits. Crude extract prepared from insoluble fractions of green and red fruits showed D-galacturonate reductase- and aldonolactonase-specific activities, the antepenultimate and penultimate enzymes, respectively, in the D-galacturonate pathway, in both fruits. Taken together, the present findings demonstrated that tomato fruits could switch between different sources for AsA supply depending on their ripening stages. The translocation from source leaves and biosynthesis via the D-mannose/L-galactose pathway are dominant sources in immature fruits, while the alternative D-galacturonate pathway contributes to AsA accumulation in ripened Micro-Tom fruits.     

Specific and unspecific responses of plants to cold and drought stress

Different environmental stresses to a plant may result in similar responses at the cellular and molecular level. This is due to the fact that the impacts of the stressors trigger similar strains and downstream signal transduction chains. A good example for an unspecific response is the reaction to stressors which induce water deficiency e.g. drought, salinity and cold, especially frost. The stabilizing effect of liquid water on the membrane bilayer can be supported by compatible solutes and special proteins. At the metabolic level, osmotic adjustment by synthesis of low-molecular osmolytes (carbohydrates, betains, proline) can counteract cellular dehydration and turgor loss. Taking the example of Pinus sylvestris, changes at the level of membrane composition, and concomitantly of photosynthetic capacity during frost hardening is shown. Additionally the effect of photoperiod as measured via the phytochrome system and the effect of subfreezing temperatures on the incidence of frost hardening is discussed. Extremely hydrophilic proteins such as dehydrins are common products protecting not only the biomembranes in ripening seeds (late embryogenesis abundant proteins) but accumulate also in the shoots and roots during cold adaptation, especially in drought tolerant plants. Dehydrins are characterized by conserved amino acid motifs, called the K-, Y-or S-segments. Accumulation of dehydrins can be induced not only by drought, but also by cold, salinity, treatment with abscisic acid and methyl jasmonate. Positive effects of the overexpression of a wild chickpea (Cicer pinnatifidum) dehydrin in tobacco plants on the dehydration tolerance is shown. The presentation discusses the perception of cold and drought, the subsequent signal transduction and expression of genes and their products. Differences and similarities between the plant responses to both stressors are also discussed.     

茶树叶片类脱水素蛋白的Western-blot分析

为了解茶树脱水素种类与功能,采用Western-blot技术,研究了不同季节及越冬过程中茶树叶片脱水素蛋白家族的表达模式。结果显示:(1)茶树叶片总蛋白提取采用酚-甲醇/醋酸铵沉淀法,用时短、蛋白浓度高、SDSPAGE电泳条带清晰,背景干净,满足茶树Western-blot技术要求。(2)在不同季节及越冬期中发现14~95kD共9种不同分子量的茶树类脱水素蛋白,其中95、65、48、37、34和14kD等6种蛋白表达量较为稳定,季节与越冬期变化不明显;58kD脱水素仅在冬季表达,越冬期不断上升,2月份增加到最高,表达丰度高;28kD脱水素蛋白在冬季表达量高,越冬期与茶树抗寒力变化规律一致;21kD脱水素在夏季和越冬期后期有较高的表达。研究表明,这3种脱水素可能在茶树抗逆中起着重要作用。     

Arabidopsis genome sequence as a tool for functional genomics in tomato

Tomato is a well-established model organism for studying many biological processes including resistance and susceptibility to pathogens and the development and ripening of fleshy fruits. The availability of the complete Arabidopsis genome sequence will expedite map-based cloning in tomato on the basis of chromosomal synteny between the two species, and will facilitate the functional analysis of tomato genes.     

Expression of KS-type dehydrins is primarily regulated by factors related to organ type and leaf developmental stage during vegetative growth

The expression of a gene, designated as DHN10, was analyzed at the protein level in two Solanum species. The DHN10 protein displays some consensus amino acid sequences of dehydrins, termed K- and S-segments. Unlike most dehydrins, both segments occur only in single copies in the DHN10 sequence and the S-segment is at a C-terminal position. Database searches revealed that KS-type dehydrins constitute a specific subclass distributed in dicotyledons and monocotyledons. In Solanum tuberosum L. plants, a high DHN10 abundance was observed under control conditions, particularly in flowers, stems, tubers and young developing leaves. In other Solanaceae and in barley (Hordeum vulgare L.), the amount of DHN10 was much more elevated in young leaves than in old leaves. DHN10 abundance was investigated in two Solanum species subjected to low temperature or to drought. Under stress conditions, we observed substantially higher protein levels only in mature expanded leaves. These findings clearly indicate that KS-type dehydrins are present at a high level in the absence of stress during vegetative growth and that their expression is primarily regulated by factors related to organ type and to leaf development stage. A potential role for the DHN10 dehydrin during plant development and in tolerance to environmental stress is discussed.Abbreviations DHN10 Dehydrin protein of 10 kDa - His Histidine - KS-type dehydrin Dehydrin containing a single K-segment followed by a single S-segment - LEA Late embryogenesis abundant - NTS Nuclear targeting signal