Desiccation tolerance of protoplasts isolated from pea embryos

To facilitate studies of desiccation tolerance at the cellular level, a technique to isolate protoplasts from desiccation-tolerant pea (Pisum sativum L. cv. Alaska) embryos has been developed. Using FDA (fluorescein diacetate) as a probe, viability of the protoplasts was investigated before and after drying to determine whether the protoplasts could survive desiccation in a manner similar to the tissue from which they were isolated. Protoplasts were isolated from 12 h imbibed pea axes, suspended in several different sugar solutions, then dried to water contents less than 0.2 g H(2)O g(-1) DW. Protoplasts only survived drying if the rate was rapid (<2 h), while slow drying (24 h) was lethal. Maximal survival (75%) was obtained after drying protoplasts with a mixture of sucrose and raffinose, while pure sucrose and trehalose were somewhat less effective protectants. Low survival was obtained after drying protoplasts with monosaccharides and pure raffinose. Protoplasts isolated from germinated seedlings did not survive dehydration below 0.2 g H(2)O g(-1) DW. Transmission electron microscopy revealed that dried desiccation-tolerant protoplasts appeared shrunken, with folded membranes, while dried protoplasts from sensitive tissue had disrupted membranes. While isolated protoplasts maintained some of the desiccation tolerance of orthodox seeds, their inability to survive complete drying and their sensitivity to drying rate is similar to the behaviour of recalcitrant embryos.     

Acquisition of desiccation tolerance in developing wheat embryos correlates with appearance of a fluid phase in membranes

Membrane behaviour in developing wheat (Triticum aestivum cv Priokskaya) embryos was studied in relation to the acquisition of desiccation tolerance, using spin probe techniques. Fresh embryos were able to develop into seedlings at day 15 after anthesis, but it took 18 d before fast‐dried, isolated embryos could germinate. On the basis of membrane integrity measurements it was estimated that between 14 and 18 d after anthesis the proportion of embryonic cells surviving fast drying increased and the critical moisture content, to which embryonic cells could be dehydrated, decreased. Apparently, embryonic cells do not acquire the same level of desiccation tolerance simultaneously. Only when all cells had become desiccation tolerant was germination of air‐dried embryos possible. Using 5‐doxylstearic acid as the probe molecule, an approximately similar lipid–water interface ordering of membranes was observed in all hydrated embryos, irrespective of age. Dehydration had a dual effect on the lipid interface: further ordering of the major part of the interface and the appearance of additional, disturbed regions. The proportion of these regions correlated with the proportion of desiccation‐tolerant cells. We propose that the membrane surface disturbance be caused by endogenous amphiphiles that partition from the cytoplasm into membranes during drying. The absence of such disturbed regions in dried, desiccation‐sensitive embryos might reflect a lack of sufficient amphiphiles. The relevance of membrane surface disturbance for desiccation tolerance is discussed.     

Desiccation tolerance in the vegetative tissues of the fern Mohria caffrorum is seasonally regulated

As there is limited information on the mechanisms of vegetative desiccation tolerance in pteridophytes, we undertook a comprehensive anatomical, ultrastructural, physiological and biochemical study on the fern Mohria caffrorum . Our data show that this species is desiccation-tolerant during the dry season, and desiccation-sensitive in the rainy season. This system allows the verification of protection mechanisms by comparison of tolerant and sensitive tissues of the same species at the same developmental age. Tolerant fronds acquire protection mechanisms during drying that are mostly similar to those reported for angiosperms. These include: (i) chlorophyll masking by abaxial scales and frond curling; (ii) increased antioxidant capacity that is maintained in dry tissues; (iii) mechanical stabilization of vacuoles in the dry state; (iv) de novo production of heat stable proteins (at least one identified as a putative chaperonin); (v) accummulation of protective carbohydrates (sucrose, raffinose family oligosaccharides and cyclitols). This study has implications for the biotechnological production of drought-tolerant crops, and allows speculation on the evolution of vegetative desiccation tolerance.     

Homeohydrous (Recalcitrant) Seeds: Dehydration, the State of Water and Viability Characteristics in Landolphia kirkii

Differential scanning calorimetry was used to study the relationships among drying rate, desiccation sensitivity, and the properties of water in homeohydrous (recalcitrant) seeds of Landolphia kirkii. Slow drying of intact seeds to axis moisture contents of approximately 0.9 to 0.7 gram/gram caused lethal damage, whereas very rapid (flash) drying of excised embryonic axes permitted removal of water to approximately 0.3 gram/gram. The amount of nonfreezable water in embryonic axes (0.28 gram H₂O/gram dry mass) did not change with drying rate and was similar to that of desiccation-tolerant seeds. These results suggest that the amount of nonfreezable water per se is not an important factor in desiccation sensitivity. However, flash drying that removed all freezable water damaged embryonic axes. Differences between desiccation-sensitive and -tolerant seeds occur at two levels: (a) tolerant seeds naturally lose freezable water, and sensitive seeds can lose this water without obvious damage only if it is removed very rapidly; (b) tolerant seeds can withstand the loss of a substantial proportion of nonfreezable water, whereas sensitive seeds are damaged if nonfreezable water is removed.     

The Positive Correlations Between the Activity of Superoxide Dismutase and Dehydration Tolerance in Wheat Seedlings

Damage to crops by drought is still a serious problem in large areas of the world. Considerable research has been undertaken to discover the mechanisms of drought injury and drought resistance of plants. However, the critical features of drought injury have not yet been identified. In the past ten years a free radical hypothesis has been suggested to account for subcellular damage caused by severe environments. Superoxide (oxygen radical) is normally produced in hydrated tissues. It is controlled by free radical scavenging reactions. One such scavenger is the enzyme superoxide dismutase (SOD). Under water stress, production of excess free radicals may occur in dehydrated plant tissues and this probably damages the membranes by causing peroxidation of the lipid components. So far few studies have been done to determine if drought injury is correlated with the free radical mechanism. In the present study, the SOD activities in wheat seedlings under water stress have been investigated by measuring the photoreduction of nitro blue tetrazolium using a spectrometric method. Meanwhile, the viabilities of wheat seedlings during drying were followed by tetrazolium test. These results provided information on the relationship between SOD activity and the dehydration tolerance of the plant. Results indicated that SOD activity changed with the time after germination. The activity of SOD of 24 h seedlings was 1.9 times higher than those of 72 h seedlings based on fresh weight. SOD activity in shoot was also higher than in root. These results were consistent with the results obtained from rating of the viabilities of seedlings during drying. The 24h seedlings were more tolerant of dehydration than 72 h seedlings and root were more sensitive of drought than shoot. In addition, shoot and root tips showed the higher SOD activities than non-tip region and they also showed a higher survival ability upon dehydration. In dehydration and subsequent rehydration, SOD activity, different from many other enzymes in plants, increased rather than declined during drying. After rehydration SOD activity returned to nearly the original level. Therefore, the positive correlations were found to exist between SOD activity and dehydration tolerance. It is reasonable to suggest that SOD enzyme may play a protective role against damage caused by free radicals which may be produced excessively during dehydration in wheat seedling.     

Changes in oligosaccharide content and antioxidant enzyme activities in developing bean seeds as related to acquisition of drying tolerance and seed quality.

Seeds of bean (Phaseolus vulgaris cv. Vernel) were collected throughout their development on the plant and dried at 15 degrees C and 75% relative humidity to a final moisture content of about 16% (fresh weight basis) to determine whether the onset of tolerance to this drying condition was related to changes in soluble sugars or the activities of the main antioxidant enzymes, namely superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR). Measurements of soluble sugars and enzyme activities were made after drying the seeds, and drying tolerance was evaluated by the ability of dried seeds to germinate and to produce normal seedlings. Seeds became tolerant to drying at 45 d after anthesis, a time marking physiological maturity. At physiological maturity, the moisture content of seeds was about 50-55% (fresh weight basis) and seed dry matter reached about 190 mg per seed. Seed vigour, evaluated by controlled deterioration and conductivity measurements, continued to increase after seed mass maturity, but decreased when seeds remained thereafter for more than 7 d on the plant. Acquisition of drying tolerance was coincident with an accumulation of raffinose and stachyose. Dried-tolerant seeds were also characterized by a high amount of sucrose, the most abundant sugar, and by a low content of monosaccharides. The (raffinose+stachyose)/sucrose ratio increased during seed filling, reaching a value close to 1 when all the seeds became tolerant to drying, and maintaining this proportion during the final stages of maturation. Acquisition of drying tolerance was also related to a reorientation of the enzymatic antioxidant defence system. Drying-tolerant dried seeds displayed high CAT and GR activities and low SOD and APX activities, while the opposite condition was observed in immature dried seeds. The shift in antioxidant enzymes corresponded to the beginning of the maturation-drying phase. These results suggest that oligosaccharide metabolism and enzymatic antioxidant defences may be involved in acquisition of drying tolerance during bean seed development, but are not related to seed vigour.     

Contents of sugars in leaves of drying desiccation tolerant flowering plants, particularly grasses

Sugar complements were analysed in extracts from leaves of desiccation tolerant species in the angiosperm families Cyperaceae, Gesneriaceae, Liliaceae, Poaceae and Velloziaceae. Total sugar content was higher in live air-dry leaves of all desiccation tolerant species (except the grass Eragrostiella nardoides; 22 µmoles/g dw) than in the dead air-dry leaves of the desiccation sensitive grass Sporobolus pyramidalis (36 µmoles/g dw). Sucrose contents rose to high levels (40–98 µmoles/g dw) in live air-dry leaves of all species (except the grass Eragrostiella nardoides in which it rose to only 11 µmoles/g dw) to become the predominant sugar. Glucose and/or fructose contents frequently were lower after leaf drying but usually these were the sugars of next highest contents in live air-dry leaves. Contents of raffinose (that has been postulated to reduce sucrose crystallization) rose to c. 10% of sucrose contents in air-dry leaves of most desiccation tolerant species (but only c. 4% in Tripogon jacquemontii) compared with c. 2% of sucrose contents in the sensitive grass S. pyramidalis. Trehalose (a rare sugar in seed-plants) was present in all but one desiccation tolerant species (Xerophyta villosa) but only in minor amounts. The results are consistent with the views that sugars play a protective role during drying of desiccation tolerant plants in general but that other factors are also involved indesiccation tolerance, that in desiccation tolerant angiospermae sucrose is generally the predominant protective sugar and that raffinose and trehalose may supplement the role of sucrose.     

Survival of root‐lesion nematodes (Pratylenchus thornei) after wheat growth in a vertisol is influenced by rate of progressive soil desiccation

The root‐lesion nematode (Pratylenchus thornei) is a major pathogen of wheat in the subtropical grain region of eastern Australia. Experiments were conducted to learn whether soil desiccation can account for the rapid fall in peak P. thornei population densities noted in the field after wheat matures. The decline in population densities of P. thornei after growth of wheat was measured on progressive desiccation of soil with roots by fast and slow drying methods. The vertisolic soil of initial moisture content 45% w/w (or matric potential of pF 3.3) was dried in 5% decrements to an air‐dried gravimetric moisture content of 15% (pF 5.6) taking 10.7 h for fast drying and 91.5 h for slow drying. After drying, live nematodes were extracted with Whitehead trays for 2 and 7 days and counted in four life stages (adults and juvenile stages J2, J3 and J4). Fast drying resulted in a sigmoidal decline in total P. thornei with only 5% of the population alive in soil at 15% moisture content, but slow drying had no significant effect on the population density. The percentage of nematodes extracted at 2 days compared with the total extracted over 7 days in undried soil (～89% of total) declined quadratically on desiccation to be 48% (fast drying) and 78% (slow drying) at 15% moisture content. With fast drying, the proportion of adults and J2 decreased whereas the proportion of J4 increased as the soil dried. With slow drying, the proportion of J2 and J3 stages decreased while the proportion of J4 increased. Thus the J4 or pre‐adult was the life stage most tolerant of soil desiccation. Time is required for P. thornei to go into a state of anhydrobiosis as a soil dries and this information can be used to model P. thornei survival in the field based on environmental parameters.     

Water Content, Raffinose, and Dehydrins in the Induction of Desiccation Tolerance in Immature Wheat Embryos

Desiccation tolerance is initiated in wheat (Triticum aestivum L.) embryos in planta at 22 to 24 d after anthesis, at the time that the embryo water content has decreased from about 73% fresh weight (2.7 g water/g dry weight) to about 65% fresh weight (1.8 g water/g dry weight). To determine if desiccation tolerance is fully induced by the loss of a relatively small amount of water, detached wheat grains were treated to reduce the embryo water content by just a small amount to approximately 69% (2.2 g water/g dry weight). After 24 h of such incipient water loss, subsequently excised embryos were able to withstand severe desiccation, whereas those embryos that had not previously lost water could not. Therefore, a relatively small decrease in water content for only 24 h acts as the signal for the development of desiccation tolerance. Embryos that were induced into tolerance by a 24-h water loss had no detectable raffinose. The oligosaccharide accumulated at later times even in embryos of detached grains that had not become desiccation tolerant, although tolerant embryos (i.e. those that previously had lost some water) contained larger amounts of the carbohydrate. It is concluded that desiccation tolerance and the occurrence of raffinose are not correlated. Immunodetected dehydrins accumulated in embryos in planta as desiccation tolerance developed. Detachment of grains induced the appearance of dehydrins at an earlier age, even in embryos that had not been made desiccation tolerant by incipient drying. It is concluded that a small reduction in water content induces desiccation tolerance by initiating changes in which dehydrins might participate but not by their interaction with raffinose.     

成熟脱水对种子发育和萌发的作用

成熟脱水是正常性种子发育的末端事件。种子在成熟时胚的脱水耐性增加;当种子萌发时胚变得不耐脱水。当种子获得脱水耐性时,糖、蛋白质和抗氧化防御系统等保护性物质积累;当脱水耐性丧失时,这些物质被降解。成熟脱水是种子从发育过程向萌发过程转变的“开关”,它降低发育的蛋白质和ｍＲＮＡ的合成,终止发育事件和促进萌发事件。顽拗性种子不经历成熟脱水的发育阶段,对脱水高度敏感。     

Ultrastructural Evidence for the Effects of Freezing in Embryonic Axes of Pisum sativum L. at Various Water Contents

This study investigated the effects of rapid drying (in an airstream) and rapid freezing (in sub-cooled liquid nitrogen) onthe survival and ultrastructural preservation of pea embryonicaxes that had been imbibed for 4 h (desiccation tolerant) and24 h (desiccation sensitive). Maximum survival of all axes inthe absence of freezing was attained. Similarly, 100% survivalwas obtained if freezing was preceded by rapid drying. Axesimbibed for 24 h and not dried were more sensitive to freezingthan undried, 4 h imbibed axes. Ultrastructural examinationshowed no organellar or cytomatrical deformations in axes fromany of the treatments. Some cells of the 24 h imbibed axes showedlocalized plasmalemma abnormalities after railed dehydration.Subsequent to freezing, irregular nuclei were observed and plasmalemmavesiculation occurred. If these axes were not dried prior tofreezing, plasmalemma vesiculation became prominent, clumpingof the cytoskeleton occurred and some wall abnormalities becameapparent. Rapid drying probably increases intercellular soluteconcentrations, and sub-cooled liquid nitrogen will increasethe rate of heat exchange between tissue and cryogen. A combinationof rapid drying and rapid freezing may obviate, or reduce, therequirement for cryoprotectants on freezing of desiccation sensitivetissue.Copyright 1995, 1999 Academic Press Pisum sativum L., pea, embryonic axis, ultrastructure, transmission electron microscopy, cryopreservation, rapid freezing     

Metabolic dysfunction and unabated respiration precede the loss of membrane integrity during dehydration of germinating radicles

This study shows that dehydration induces imbalanced metabolism before loss of membrane integrity in desiccation-sensitive germinated radicles. Using a photoacoustic detection system, responses of CO(2) emission and fermentation to drying were analyzed non-invasively in desiccation-tolerant and -intolerant radicles of cucumber (Cucumis sativa) and pea (Pisum sativum). Survival after drying and a membrane integrity assay showed that desiccation tolerance was present during early imbibition and lost in germinated radicles. However, tolerance could be re-induced in germinated cucumber radicles by incubation in polyethylene glycol before drying. Tolerant and polyethylene glycol (PEG)-induced tolerant radicles exhibited a much-reduced CO(2) production before dehydration compared with desiccation-sensitive radicles. This difference was maintained during dehydration. In desiccation-sensitive tissues, dehydration induced an increase in the emission of acetaldehyde and ethanol that peaked well before the loss of membrane integrity. Acetaldehyde emission from sensitive radicles was significantly reduced when dehydration occurred in 50% O(2) instead of air. Acetaldehyde/ethanol were not detected in dehydrating tolerant radicles of either species or in polyethylene glycol-induced tolerant cucumber radicles. Thus, a balance between down-regulation of metabolism during drying and O(2) availability appears to be associated with desiccation tolerance. Using Fourier transform infrared spectroscopy, acetaldehyde was found to disturb the phase behavior of phospholipid vesicles, suggesting that the products resulting from imbalanced metabolism in seeds may aggravate membrane damage induced by dehydration.     

Effect of the antioxidant ionol on proteolytic apparatus of aging coleoptiles of wheat seedlings grown in light

The dynamics of changes in total proteolytic activity and activities of various groups of proteases in the coleoptiles of 3- to 12-day-old wheat seedlings grown in light with and without antioxidant BHT (2,6-di-tert-butyl-4-methylphenol) was studied. It was established that the specialized proteases that easily hydrolyze specific synthetic substrates and the enzymes actively hydrolyzing histone H1 dominate in young coleoptiles of 3- to 4-day-old seedlings. Proteases that degrade equally well the majority of the studied substrates are accumulated in the cells of old coleoptiles of 11- to 12-day-old seedlings. Under the effect of BHT, the plants grown in light (in comparison with etiolated seedlings) demonstrated a somewhat changed dynamics of proteolytic activity in young coleoptiles and the disappearance of proteases active toward histone H1. An inhibitory analysis revealed a relative domination of cysteine proteases in young coleoptiles at the initial development stage of seedlings, whereas the fraction of serine proteases markedly increased in old coleoptiles. We presume that the revealed quantitative and qualitative changes in the proteolytic apparatus of the coleoptile cells induced by BHT may be largely responsible for the retardant and geroprotective effect of this antioxidant in plants.     

Increased rate of drying reduces metabolic inequity and critical water content in radicles of Cicer arietinum L.

Orthodox seed serves as easily accessible model to study desiccation-sensitivity in plant tissues because once they undergo germination, they become sensitive to desiccation imposed injuries. In the proposed study, effects of rate of drying on the viability, electrolyte leakage, superoxide accumulation, lipid-protein oxidation and antioxidant enzymes were explored in excised radicles of Cicer arietinum L. under dehydration and wet storage. For both the drying conditions, desiccation could be explained by exponential and inverse functions. Under rapid drying tissue viability as scored by germination efficiency and tetrazolium staining remained 100 % all through the analysis (24 h) but declined remarkably after 0.30 g g⁻¹ fresh mass water content (4 days) under slow drying. Moreover, precipitous fall in tissue viability was observed after 2 weeks of wet storage. Rapid drying was also accompanied with limited amounts of electrolyte leakage, superoxide radical, malondialdehyde and protein hydroperoxide, together with enhanced level of protein. Additionally, activities of both superoxide dismutase and ascorbate peroxidase were increased in rapidly dried radicles, but guaiacol peroxidase was declined. In contrary, above referred biomarkers were observed to perform either inversely or poorly during slow drying and wet storage suggesting that above documented alterations might be the resultant of ageing and not desiccation. Gathered data demonstrated that increased drying lowers the critical water content for tissue survival and also reduces the risk of damage resulting from aqueous-based deleterious reactions. Additionally, it also showed that growing radicles are a popular model to explore desiccation-sensitivity in plant tissues and/or seeds.     

Effect of Antioxidant BHT on the Proteolytic Apparatus of Aging Coleoptiles of Wheat Seedlings Grown in Light

The dynamics of changes in total proteolytic activity and activities of various groups of proteases in the coleoptiles of 3- to 12-day-old wheat seedlings grown in light with and without antioxidant BHT (2,6-di-tert-butyl-4-methylphenol) was studied. It was established that the specialized proteases that easily hydrolyze specific synthetic substrates and the enzymes actively hydrolyzing histone H1 dominate in young coleoptiles of 3- to 4-day-old seedlings. Proteases that degrade equally well the majority of the studied substrates are accumulated in the cells of old coleoptiles of 11- to 12-day-old seedlings. Under the effect of BHT, the plants grown in the light (in comparison with etiolated seedlings) demonstrated a somewhat changed dynamics of proteolytic activity in young coleoptiles and the disappearance of proteases active toward histone H1. An inhibitory analysis revealed a relative domination of cysteine proteases in young coleoptiles at the initial development stage of seedlings, whereas the fraction of serine proteases markedly increased in old coleoptiles. We presume that the revealed quantitative and qualitative changes in the proteolytic apparatus of the coleoptile cells induced by BHT may be largely responsible for the retardant and geroprotective effect of this antioxidant in plants.     

Sensitivity to drying in vitro of enzymes in mitochondrial subfractions from Vicia faba seed

In order to investigate the persistence of membrane and matrix functions following desiccation, enzymic activities were studied in Vicia faba L. seed mitochondrial subfractions subjected to drying and rehydration in vitro. Mitochondria were prepared after 0, 12 and 24 h of seed imbibition. These were fractionated into inner membranes ("submitochondrial particles"), outer membranes (12 and 24 h only) and the soluble matrix. Enzyme activities associated with the inner membrane and matrix were found to increase several-fold during the first 12 h of imbibition. The two matrix enzymes examined, malate dehydrogenase and glutamate dehydrogenase, were insensitive to in vitro drying at all stages of imbibition. The membrane-bound activities from 12 h and 24 h imbibed material, antimycin A-sensitive NADH: cytochrome c oxidoreductase and (F_o-F₁)-ATPase of the inner membrane and antimycin A-insensitive NADH: cytochrome c oxidoreductase of the outer membrane, were moderately sensitive to dehydration. The F₁-ATPase solubilized from the inner membrane (F_o-F₁) complex was much less sensitive to drying, provided this was done at room temperature.
Mitochondria posessing their outer membranes could not be prepared from dry seed. The antimycin A-sensitive NADH: cytochrome c oxidoreductase from inner mitochondrial membranes of unimbibed seed was extremely sensitive to desiccation in vitro, about 75 to 80% of the activity being lost. This loss could be somewhat reduced by addition of glycerol or sucrose before drying.
It is concluded that uncontrolled desiccation results in major damage to some of the membrane-bound enzymic systems in mitochondria, whereas activities in the soluble fraction are remarkably tolerant of desiccation.     

Postgenomic analysis of desiccation tolerance

Desiccation tolerance is the capacity to survive complete drying. It is an ancient trait that can be found in prokaryotes, fungi, primitive animals (often at the larval stages), whole plants, pollens and seeds. In the dry state, metabolism is suspended and the duration that anhydrobiotes can survive ranges from years to centuries. Whereas genes induced by drought stress have been successfully enumerated in tissues that are sensitive to cellular desiccation, we have little knowledge as to the adaptive role of these genes in establishing desiccation tolerance at the cellular level. This paper reviews postgenomic approaches in a variety of desiccation tolerant organisms in which the genetic responses have been investigated when they acquire the capacity of tolerating extremes of dehydration or when they are dry. Accumulation of non-reducing sugars, LEA proteins and a coordinated repression of metabolism appear to be the essential and universal attributes that can confer desiccation tolerance. The protective mechanisms of these attributes are described. Furthermore, it is most likely that other mechanisms have evolved since the function of about 30% of the genes involved in desiccation tolerance remains to be elucidated. The question of the overlap between desiccation tolerance and drought tolerance is briefly addressed.     

Effect of sodium nitroprusside on heat resistance of wheat coleoptiles: Dependence on the formation and scavenging of reactive oxygen species

The effect of nitric oxide donor sodium nitroprusside (SNP) on resistance of coleoptiles of 4-day-old etiolated seedlings of wheat (Triticum aestivum L., cv. Elegiya) to damaging heating (10 min at 43°C) and possible dependence of this effect on changes in the activities of enzymes producing and scavenging reactive oxygen species (ROS) were studied. Treatment of coleoptiles with 500 μM SNP considerably boosted generation of superoxide anion radical therein. This effect was substantially suppressed by blocker of calcium channels (lanthanum chloride), calmodulin antagonist (chlorpromazine), and inhibitor of NADPH-oxidase (imidazole) but not by peroxidase inhibitor (salicylhydroxamic acid). NO donor activated antioxidant enzymes (superoxide dismutase, catalase, and soluble peroxidase) and elevated heat resistance of wheat coleoptiles. NO scavenger methylene blue, antioxidant agent ionol, calcium antagonists, and NADPH-oxidase inhibitor imidazole substantially reduced the elevation of heat resistance of wheat coleoptiles induced by NO donor. It was concluded that SNP-induced heat resistance of coleoptiles depended on calcium and ROS, whose production is probably boosted by activation of NADPH-oxidase.     

成熟脱水对种子发育和萌发的作用

成熟脱水是正常性种子发育的末端事件。种子在成熟时胚的脱水耐性增加;当种子萌发时胚变得不耐脱水。当种子获得脱水耐性时,糖、蛋白质和抗氧化防御系统等保护性物质积累;当脱水耐性丧失时,这些物质被降解。成熟脱水是种子从发育过程向萌发过程转变的“开关”,它降低发育的蛋白质和mRNA的合成,终止发育事件和促进萌发事件。顽拗性种子不经历成熟脱水的发育阶段,对脱水高度敏感。     

Drought tolerance depends on the age of the spring wheat seedlings and differentiates patterns of proteinases

The majority of plant species lose their ability to tolerate severe water deficit after germination at the beginning of seedling growth, in the time of emergence of the radical from the seed. The experiment was designed to compare the differences in proteolytic response between 4-and 6-days old spring wheat (Triticum aestivum L.) seedlings of Eta cultivar, respectively tolerant and sensitive to severe drought inducing up to 90% water saturation deficit (WSD). In coleoptiles the changes of proteolytic activity had the same trend regardless on the seedlings age and increased about fourfold upon 85% WSD as compared to the control, from about 4 to 19 (U/mg protein h). The dehydration of roots of 4 day old seedlings resulted in sharp, fivefold activity increase at 85% WSD (from 11 to >50 U/mg protein h). In roots of 6 days old seedlings dehydrated to 55% WSD the proteolytic activity raised twofold and was about 2.5 times higher than in roots of 4 days old seedlings dehydrated to the same WSD. In coleoptiles of both the 4- and 6-days old seedlings subjected to drought appearance of new bands of serine proteinases was observed. Presented results indicate that roots are more sensitive to drought than coleoptiles, which brings an argument for breeders showing that programs involving roots phenotyping have a full biochemical rationale.