Growth,sugar accumulation,and dark respiration of suspension cell cultures derived from contrasting alfalfa cultivars

Fall dormancy results in decumbent, slow shoot growth of alfalfa (Medicago sativa L.) in autumn and reduced shoot regrowth rates after herbage removal in summer. Although fall dormancy is used to predict alfalfa adaptation, we possess a poor understanding of the biological mechanisms underlying fall dormancy. Our objective was to examine growth and carbohydrate metabolism of suspension cell cultures derived from contrasting alfalfa cultivars that genetically differed in fall dormancy. Suspension cells were grown in B5h media containing 2% sucrose. Cells derived from fall non-dormant plants accumulated sugars more rapidly after transfer to fresh media and to higher concentrations than did cells derived from fall dormant alfalfa cultivars. Dark respiration rates of cells derived from non-dormant plants were similar to those derived from fall dormant plants when growth was limited at low cell sugar concentrations. However, both cell growth and dark respiration rates increased in cells derived from non-dormant cultivars in response to greater cell sugar concentrations. High growth rates of cells derived from rapid growing, fall non-dormant alfalfa cultivars were associated with rapid sugar uptake and higher cell respiration rates when compared to cells derived from dormant alfalfa cultivars.     

Drought survival,summer dormancy and dehydrin accumulation in contrasting cultivars of Dactylis glomerata

To study survival under prolonged and severe drought in the perennial grass Dactylis glomerata we compared dormant, resistant and sensitive cultivars (cvs.) in both field and glasshouse experiments. Water status, membrane stability and expression of dehydrins were assessed in the immature leaf bases, which are the last surviving organs. Analysis of leaf elongation and senescence of aerial tissues showed that dormancy was exhibited by the potentially dormant cultivar (cv.) only in the field. This cultivar exhibited a high survival rate, similar levels of dehydration and expression of a low-molecular weight (22–24 kDa) dehydrin in both drought and irrigated plants, whether fully dormant or not. At the same level of soil water deficit, there were no differences between the non-dormant drought resistant and drought sensitive cultivars in plant water status and membrane stability. However, the accumulation of dehydrins as drought progressed was markedly different between these cultivars and was associated with their contrasting survival. The possible role of the major low-molecular dehydrins in maintenance of cell integrity under dehydration is discussed with reference to both summer dormancy and survival under severe drought.     

Redox-sensitive proteome and antioxidant strategies in wheat seed dormancy control

Oxidative signalling by ROS has been demonstrated to play a role in seed dormancy alleviation, but the detailed molecular mechanisms underlying this process remain largely unknown. Here, we show dynamic differences in redox-sensitive proteome upon wheat seed dormancy release. Using thiol-specific fluorescent labelling, solubility-based protein fractionation, 2-D IEF PAGE, and MS analysis in conjunction with wheat EST sequence libraries, proteins with reversible oxidoreductive changes were characterized. Altogether, 193 reactive Cys were found in 79 unique proteins responding differentially in dormant, non-dormant, abscisic, or gibberellic acid-treated seed protein extracts from RL4137, a wheat cultivar with extreme dormancy. The identified proteins included groups that are redox-, stress-, and pathogen-responsive, involved in protein synthesis and storage, are enzymes of carbohydrate metabolism, proteases, and those involved in transport and signal transduction. Two types of redox response could be detected: (i) a dramatic increase in protein thiol redox state in seeds during imbibition and hormonal treatment; (ii) higher antioxidant capacity related to sensing of a threshold redox potential and balancing the existing redox pools, in dry dormant versus non-dormant seeds. These results highlight occurrence of the antioxidant defence mechanisms required for the protection of seed during a dormancy stage.     

Secondary dormancy in Avena fatua: Induction and characteristics in genetically pure dormant lines

The induction of secondary dormancy in caryopses of genetically pure dormant lines of Avena fatua L. is described. Seeds harvested from mature plants were after-ripened under controlled conditions (26°C, 25% relative humidity) until fully non-dormant. Secondary dormancy was then induced into these caryopses by incubation on moist filter papers in an aspirated nitrogen atmosphere at 20°C over periods from 3 h to 14 days. These caryopses failed to germinate when returned to an aerobic environment. The dose-response curves for gibberellic acid, sodium azide, sodium nitrite, sodium nitrate and ethanol show that all of these treatments can overcome the induced secondary dormancy. Drying increased the sensitivity of secondary dormant caryopses to these treatments. These treatments overcame secondary dormancy at all times, indicating the presence of only one of the two known blocks to germination that exist during primary dormancy. Similarities between primary and secondary dormancy in A. fatua are discussed.     

Protein Synthesis in Dormant and Non-Dormant Cocklebur Seed Segments

Using the axial and cotyledonary segments of lower cocklebur (Xanthium pensylvanicum Wallr.) seeds, protein synthesis as shown by incorporation of radioactive leucine was examined in relation to their dormant status. During the first 9 h of water imbibition, the protein synthesis was higher in the dormant axes than in the non-dormant, after- ripened ones. When imbibed for more than 12 h non-dormant axes had a higher activity than dormant ones. This was also the case with the cotyledonary segments. Cyctoheximide, an inhibitor of protein synthesis, blocked protein synthesis in the axial tissue regardless of its dormant status, and thereby inhibited germination of the non-dormant seeds. In the dormant seeds, however, cycloheximide at 3 mM slightly stimulated germination without stimulating the C₂H₄ production. Based on these results, it is suggested that in cocklebur seeds there may be some proteinaceous system which is involved in the maintenance of dormancy.     

Adaptive responses to drought of two Retama raetam subspecies from Tunisia

两个突尼斯细枝豆属植物亚种对干旱的适应性响应 干旱生境植物的生存和生态分布主要取决于水的可获得性以及植物抵御干旱的生理适应能力。在 本研究中，我们比较了来自突尼斯的细枝豆属植物Retama raetam的两个亚种对干旱的生理响应，其中一 种生长在沙漠气候下(raetam亚种)，另一种生长于海岸带(bovei亚种)。为了对这两个亚种进行生理表征并揭示它们耐旱性的主要机制，从受干旱胁迫最长达一个月的四月龄植株中获取了多项参数，涉及植株的萌发、生长、光合作用(净光合速率、细胞内CO₂浓度、蒸腾速率、气孔导度和水分利用效率)和渗透物(脯氨酸、甜菜碱和总可溶性糖)积累等。研究结果表明，干旱会显著抑制植株的萌发、生长，对所研究的各项光合参数也都产生很大的负面影响。经过3周的处理后，bovei亚种受到了干旱条件的显著影响，其光合作用速率与对照相比最高下降了7倍。与此同时，该亚种中出现了对脯氨酸和甜菜碱的显著积累(相较于灌溉条件下的对照)，但远低于raetam亚种；在raetam亚种中，脯氨酸和甜菜碱分别增加至相应对照的24和6倍。综上所述，相较于生长在半干旱海岸气候下的细枝豆属植物种群，生长于沙漠地区的种群对干旱胁迫表现出更强的耐性，表明这种耐性在很大程度上取决于渗透物质在体内的累积。     

Seasonal patterns of growth, dehydrins and water-soluble carbohydrates in genotypes of Dactylis glomerata varying in summer dormancy

• Background and Aims Summer dormancy in perennial grasseshas been studied inadequately, despite its potential to enhanceplant survival and persistence in Mediterranean areas. The aimof the present work was to characterize summer dormancy anddehydration tolerance in two cultivars of Dactylis glomerata(dormant ‘Kasbah’, non-dormant ‘Oasis’)and their hybrid using physiological indicators associated withthese traits. • Methods Dehydration tolerance was assessed in a glasshouseexperiment, while seasonal metabolic changes which produce putativeprotectants for drought, such as carbohydrates and dehydrinsthat might be associated with summer dormancy, were analysedin the field. • Key Results The genotypes differed in their ability tosurvive increasing soil water deficit: lethal soil water potential(_s) was –3·4 MPa for ‘Kasbah’ (althoughnon-dormant), –1·3 MPa for ‘Oasis’,and –1·6 MPa for their hybrid. In contrast, lethalwater content of apices was similar for all genotypes (approx.0·45 g H₂O g d. wt^–1), and hence the greater survivalof ‘Kasbah’ can be ascribed to better drought avoidancerather than dehydration tolerance. In autumn-sown plants, ‘Kasbah’had greatest dormancy, the hybrid was intermediate and ‘Oasis’had none. The more dormant the genotype, the lower the metabolicactivity during summer, and the earlier the activity declinedin spring. Decreased monosaccharide content was an early indicatorof dormancy induction. Accumulation of dehydrins did not correlatewith stress tolerance, but dehydrin content was a function ofthe water status of the tissues, irrespective of the soil moisture.A protein of approx. 55 kDa occurred in leaf bases of the mostdormant cultivar even in winter. • Conclusions Drought avoidance and summer dormancy arecorrelated but can be independently expressed. These traitsare heritable, allowing selection in breeding programmes.     

Physiological,biochemical and morphoagronomic characterization of drought-tolerant and drought-sensitive bean genotypes under water stress

Water deficit is one of the main factors that reduce grain yield. A better understanding of the mechanisms related to this abiotic stress is a key aspect to design and act upon drought tolerance improvement in crop plants. Therefore, the major objective of this study was to investigate four common bean genotypes for drought tolerance and to establish their tolerance mechanisms. The experiment was carried out in a greenhouse, using the completely randomized design in a factorial arrangement (2?×?4), composed by 2 water conditions (well-watered and water deficit) and 4 cultivars, with six replicates per treatment. The four cultivars, two drought-sensitive (IAC Tybatã and BRS Pontal) and two drought-tolerant (IAPAR 81 and BAT 477), were evaluated for some physiological, biochemical and morphoagronomic traits. Drought promoted physiological and metabolic changes in the plants, reflecting on the morphoagronomic traits. Under water deficit, the genotype IAPAR 81 stood out from the others in terms of physiological characters, however, it presented a low efficiency concerning biochemical activities and a significant reduction in the morphoagronomic characters. The cultivar BAT 477 demonstrated to be drought-adapted presenting more efficient biochemical and morphoagronomic adaptions and the genotype BRS Pontal obtained morphoagronomic values similar to BAT 477, thus it may be classified as moderately tolerant to drought.     

Physiological and Environmental Requirements for Poplar (Populus deltoides) Bark Storage Protein Degradation

In poplar (Populus deltoides Bartr. ex Marsh), a 32-kD bark storage protein (BSP) accumulates in the bark during autumn and winter and declines during spring shoot growth. We investigated the physiological and environmental factors necessary for the degradation of poplar BSP. Poplar plants were exposed to short-day (SD) photoperiods for either 28 or 49 d. Plants exposed to short days for 28 d formed a terminal bud but were not dormant, whereas exposure to short days for 49 d induced bud dormancy. BSP accumulated in bark of plants exposed to both SD treatments. The level of BSP declined rapidly when nondormant plants were returned to long days. BSP levels did not decline in dormant plants that were exposed to long-day (LD) conditions. If dormant plants were first treated with either low temperatures (0[deg]C for 28 d) or with 0.5 M H2CN2 to overcome dormancy and then returned to long days, the level of BSP declined. Removal of buds from non-dormant or dormant plants in which dormancy had been overcome inhibited the degradation of BSP in LD conditions. BSP mRNA levels rapidly declined in plants exposed to long days, irrespective of the dormancy status of the plants or the presence or absence of buds. These results indicate that the buds of poplars are somehow able to communicate with bark storage sites and regulate poplar BSP degradation. These results further support an association of BSP mRNA levels with photoperiod because short days stimulate BSP mRNA accumulation, whereas long days result in a decline of BSP mRNA abundance.     

The Effects of Temperature and Photoperiod on the Onset of Summer Dormancy in Poa bulbosa L.

Poa bulbosa L. plants became dormant in long days (16 h), whilein short days (8 h) they remained non-dormant for extended periods.Morphologically, the onset of dormancy was expressed by theformation of a true bulb at the base of every tiller, by thecessation of tillering and leaf emergence and, finally, by thedrying-up of the leaves. Low temperature delayed the onset ofdormancy but did not prevent it. This effect of temperaturemay explain the delayed onset of dormancy observed in naturalpopulations under a cool climate at a hilly habitat, comparedto plants growing under a warmer climate, at a lower, coastal-plainhabitat. Dormancy could be induced under short days by pre-exposureof the plants to a limited number of long days. The responsewas proportional to the number of long days given. The adaptivesignificance of the results for plant survival in a Mediterraneanclimate is discussed. Poa bulbosa L., summer dormancy, photoperiod, temperature, leaf emergence, bulbs, tillers     

Abscisic acid-regulated responses of dormant and non-dormant embryos of Helianthus annuus: Role of ABA-inducible proteins

Embryos of Helianthus annuus L. became dormant 3 weeks after anthesis and their dormancy was lifted during storage in dry conditions. The objectives of this study were to investigate changes in the pattern of soluble proteins associated with the release of embryo dormancy. Sunflower dehydrins and group 3 late embryogenesis-abundant (LEA) proteins were studied in developing embryos. Three dehydrins (17, 21 and 26 kDa) and two group 3 LEA polypeptides (17 and 23 kDa) appeared during dormancy induction. Their levels remained steady until maturity. After imbibition, these polypeptides disappeared within 24 h except for the 23-kDa protein whose levels remained stable for a further 4 d, whatever the culture condition. Analysis of radiolabelled proteins by two-dimensional gel electrophoresis revealed that among dormancy-associated proteins other than dehydrin and group 3 LEA, several low molecular mass (18, 19, 20 and 21 kDa) proteins were expressed in dormant embryos but not detected in non-dormant embryos. After a treatment with fluridone, which inhibits ABA synthesis, or with GA₃, which allows germination to occur, the 19-kDa protein could not be detected. In contrast, application of ABA to non-dormant embryos arrested germination and enhanced the synthesis of the 18- and 21-kDa proteins, but not that of the 19- and 20-kDa polypeptides. These results demonstrate that steady-state levels of specific proteins change during early imbibition of dormant and non-dormant sunflower embryos and indicate that these changes may be associated with differential gene expression responsible for the maintenance of dormancy.