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.     

The distribution of zinc,cadmium, lead and copper within the woodlouse Oniscus asellus (Crustacea,Isopoda)

Summary The concentrations of zinc, cadmium, lead and copper have been determined in the hepatopancreas, hindgut and rest of the body tissues of Oniscus asellus collected from eight sites in the U.K. The hepatopancreas is by far the most important storage organ of heavy metals, particularly cadmium, and at each site, contains a mean of at least 89% of the total body load of this element. Specimens of Oniscus asellus from contaminated sites may contain concentrations of zinc, cadmium, lead and copper in the hepatopancreas of about 1%, 0.5%, 2.5% and 3% of the dry weight respectively, which are among the highest so far recorded in the soft tissues of any animal.There is a significant positive correlation between the mean relative dry weight of the hepatopancreas of Oniscus asellus and the concentrations of zinc or cadmium in leaf litter from all eight sites. It is suggested that animals from sites which are contaminated heavily with zinc or cadmium have a large hepatopancreas because this enables them to de-toxify a greater amount of the metal.     

Effects of starvation and dehydration on osmotic and ionic balance in Carausius morosus

This study describes the effects that prolonged desiccation has on osmotic and ionic balance in Carausius morosus, an insect with a rather unusual haemolymph composition (it is rich in divalent cations and has a low sodium content). After 7 days at 0% r.h., there is a 50 per cent decrease in water content of the animal. This loss is largely confined to the haemolymph, which declines in volume to about one-seventh of its previous value. In spite of these drastic changes, the osmotic concentration of the haemolymph increases only by about 20 per cent while the concentrations of the main blood ions increase by similar or smaller amounts. So, as with other insects so far examined, Carausius turns out to have very effective control of the osmotic and ionic concentrations of its internal milieu in the face of severe stress upon it.     

Water balance and the mantle cavity fluid of Nucella lapillus(L.) (Mollusca: Prosobranchia)

When uncovered by the tide Nucella lapillus (L.) retains fluid in the mantle cavity which accounts for ≈ 39% of the total water content of the attached animal. This extra-corporeal fluid reservoir retained in the mantle cavity has been investigated in relation to desiccation. Volume changes of mantle cavity fluid (m.c.f.) and concentration changes in Cl^?, Na⁺ and total osmotic pressure of m.c.f. and blood, suggest that the m.c.f. reduces the full effects of desiccation on the animal by restricting those effects to the external compartment. The blood of Nucella living in normal sea water was found to be hypo-osmotic and an hypothesis is presented which links this to the rôle of the m.c.f. during desiccation.     

QTLs and candidate genes for desiccation and abscisic acid content in maize kernels

Background

Kernel moisture at harvest is an important trait since a low value is required to prevent unexpected early germination and ensure seed preservation. It is also well known that early germination occurs in viviparous mutants, which are impaired in abscisic acid (ABA) biosynthesis. To provide some insight into the genetic determinism of kernel desiccation in maize, quantitative trait loci (QTLs) were detected for traits related to kernel moisture and ABA content in both embryo and endosperm during kernel desiccation. In parallel, the expression and mapping of genes involved in kernel desiccation and ABA biosynthesis, were examined to detect candidate genes.

Results

The use of an intermated recombinant inbred line population allowed for precise QTL mapping. For 29 traits examined in an unreplicated time course trial of days after pollination, a total of 78 QTLs were detected, 43 being related to kernel desiccation, 15 to kernel weight and 20 to ABA content. Multi QTL models explained 35 to 50% of the phenotypic variation for traits related to water status, indicating a large genetic control amenable to breeding. Ten of the 20 loci controlling ABA content colocated with previously detected QTLs controlling water status and ABA content in water stressed leaves. Mapping of candidate genes associated with kernel desiccation and ABA biosynthesis revealed several colocations between genes with putative functions and QTLs. Parallel investigation via RT-PCR experiments showed that the expression patterns of the ABA-responsive Rab17 and Rab28 genes as well as the late embryogenesis abundant Emb5 and aquaporin genes were related to desiccation rate and parental allele effect. Database searches led to the identification and mapping of two zeaxanthin epoxidase (ZEP) and five novel 9-cis-epoxycarotenoid dioxygenase (NCED) related genes, both gene families being involved in ABA biosynthesis. The expression of these genes appeared independent in the embryo and endosperm and not correlated with ABA content in either tissue.

Conclusions

A high resolution QTL map for kernel desiccation and ABA content in embryo and endosperm showed several precise colocations between desiccation and ABA traits. Five new members of the maize NCED gene family and another maize ZEP gene were identified and mapped. Among all the identified candidates, aquaporins and members of the Responsive to ABA gene family appeared better candidates than NCEDs and ZEPs.     

Physical features and chitin content of eggs from the mosquito vectors Aedes aegypti,Anopheles aquasalis and Culex quinquefasciatus: Connection with distinct levels of resistance to desiccation

Mosquito eggs are laid in water but freshly laid eggs are susceptible to dehydration, if their surroundings dry out at the first hours of development. During embryogenesis of different mosquito vectors the serosal cuticle, an extracellular matrix, is produced; it wraps the whole embryo and becomes part of the eggshell. This cuticle is an essential component of the egg resistance to desiccation (ERD). However, ERD is variable among species, sustaining egg viability for different periods of time. While Aedes aegypti eggs can survive for months in a dry environment (high ERD), those of Anopheles aquasalis and Culex quinquefasciatus in the same condition last, respectively, for one day (medium ERD) or a few hours (low ERD). Resistance to desiccation is determined by the rate of water loss, dehydration tolerance and total amount of water of a given organism. The ERD variability observed among mosquitoes probably derives from diverse traits. We quantified several attributes of whole eggs, potentially correlated with the rate of water loss: length, width, area, volume, area/volume ratio and weight. In addition, some eggshell aspects were also evaluated, such as absolute and relative weight, weight/area relationship (herein called surface density) and chitin content. Presence of chitin specifically in the serosal cuticle as well as aspects of endochorion external surface were also investigated. Three features could be related to differences on ERD levels: chitin content, directly related to ERD, the increase in the egg volume during embryogenesis and the eggshell surface density, which were both inversely related to ERD. Although data suggest that the amount of chitin in the eggshell is relevant for egg impermeability, the participation of other yet unidentified eggshell attributes must be considered in order to account for the differences in the ERD levels observed among Ae. aegypti, An. aquasalis and Cx. quinquefasciatus.     

Effect of relative humidity on water content, viability and carbohydrate profile of Petunia hybrida and Cucurbita pepo pollen

Petunia hybrida and Cucurbita pepo pollen was exposed to 30 and 75% relative humidity (RH). Water content, viability and carbohydrate content (glucose, fructose, sucrose and starch) were measured at fixed intervals over 6 h. Water content of C. pepo pollen decreased drastically at both RHs, while P. hybrida pollen dehydrated slightly at RH 30% and hydrated at RH 75%. The pollen of the two species also showed very different sensitivity to dehydration. P. hybrida pollen was resistant to desiccation, with viability remaining around 80% throughout the experiment, whereas C. pepo was very sensitive to desiccation, showing an abrupt decrease in viability when its water content reached about 13% (fresh weight basis) at both RHs. Carbohydrate content was also different in the two species. Sucrose content increased soon after dehydration of P. hybrida pollen at RH 30%, whereas it remained almost constant in C. pepo pollen at the same RH. The results are discussed in the framework of basic pollen physiology and of plant reproductive strategy.     

Accumulation of soluble sugars, heat-stable proteins and dehydrins in cryopreservation of protocorm-like bodies ofDendrobium candidumby the air-drying method

Protocorm-like bodies (PLBs) of Dendrobium candidum were successfully cryopreserved by the air-drying method. The optimal water content before freezing seemed to be at the range of 0.1 g H₂O/g DW (11 % on fresh weight basis) to 0.5 g H₂O/g DW (33 % on fresh weight basis). Changes in soluble sugars, heat-stable proteins and dehydrins during desiccation of PLBs were analyzed. Extensive accumulation of soluble sugars was observed at water content of about 7.2 g H₂O/g DW (after 24 h desiccation), and the sugars content did not increase further during the following desiccation. The amount of heat-stable protein increased significantly when water content decreased to 1.0 g H₂O/g DW (after approximately 66 h desiccation). Results from immunological detection showed that two bands of the heat-stable proteins with respective molecular masses of 28.7 and 34.3 kDa were dehydrins which appeared when water content dropped to 1.0 g H₂O/g DW. Therefore, it seemed that accumulation of dehydrins happened later than that of soluble sugars. Interestingly, exogenous ABA treatment of PLBs before desiccation could also induce the accumulation of soluble sugars, heat-stable proteins and dehydrins. The possible roles of these substances in the acquisition of dehydration and freezing tolerance were discussed.     

Effect of desiccation level and storage temperature on green spore viability of Osmunda japonica

In order to effectively preserve green spores, which have relatively higher water content and lose viability more quickly than non-green spores, we studied the effect of desiccation level and storage temperature on Osmunda japonica spores. The water content of fresh spores was 11.20%. After 12 h desiccation by silica gel, the water content decreased to 6% but spore viability did not change significantly. As the desiccation continued, the decrease in water content slowed, but spore viability dropped. For almost all storage periods, the effects of storage temperature, desiccation level, and temperature × desiccation level were significantly different. After seven days of storage, spores at any desiccation level stored at 4 °C obtained high germination rates. After more than seven days storage, liquid nitrogen (LN) storage obtained the best results. Storage at −18 °C led to the lowest germination rates. Spores stored at room temperature and −18 °C all died within three months. For storage at 4 °C and in LN, spores desiccated 12 and 36 h obtained better results. Spores without desiccation had the highest germination rates after being stored at room temperature, but suffered the greatest loss after storage at −18 °C. These results suggest that LN storage is the best method of long-term storage of O. japonica spores. The critical water content of O. japonica spores is about 6% and reduction of the water content to this level improves outcome after LN storage greatly. The reason for various responses of O. japonica spores to desiccation and storage temperatures are discussed.     

Water Stress and Protein Synthesis: V. Protein Synthesis, Protein Stability, and Membrane Permeability in a Drought-sensitive and a Drought-tolerant Moss

The effects have been studied of water stress and desiccation on protein synthesis in the drought-tolerant moss Tortula ruralis and the drought-sensitive moss Hygrohypnum luridum. At any particular level of steady state water stress, the inhibition of protein synthesis was greater in H. luridum than in T. ruralis. Water stress-induced changes in the pattern of protein synthesis, as determined by the double label ratio technique, were minor in T. ruralis, but major in H. luridum. Proteins of both mosses were found to be stable during desiccation and subsequent rehydration. Changes in membrane permeability, as indicated by the leakage of amino acid, were observed during rehydration of desiccated moss and were dependent on the rate of desiccation. The leakage was small and reversible in T. ruralis but large and irreversible in H. luridum. Although H. luridum failed to recover from complete desiccation (80% loss in fresh weight), it was able to recover fully from steady state stress under conditions where a maximum loss of 55% in fresh weight was recorded.     

Rapid changes in desiccation resistance in Drosophila melanogaster are facilitated by changes in cuticular permeability

Insects can improve their desiccation resistance by one or more of (1) increasing their water content; (2) decreasing water loss rate; or (3) increasing the amount of water able to be lost before death. Female Drosophila melanogaster have previously been reported to increase their resistance to desiccation after a desiccation pre-treatment and recovery, but the mechanism of this increased desiccation resistance has not been explored. We show that female, but not male adult D. melanogaster increased their resistance to desiccation after 1 h of recovery from a 3 to 4.5 h pre-treatment that depletes them of 10% of their water content. The pre-treatment did not result in an increase in water content after recovery, and there is a slight increase in water content at death in pre-treated females (but no change in males), suggesting that the amount of water loss tolerated is not improved. Metabolic rate, measured on individual flies with flow-through respirometry, did not change with pre-treatment. However, a desiccation pre-treatment did result in a reduction in water loss rate, and further investigation indicated that a change in cuticular water loss rate accounted for this decrease. Thus, the observed increase in desiccation resistance appears to be based on a change in cuticular permeability. However, physiological changes in response to the desiccation pre-treatment were similar in male and female, which therefore does not account for the difference in rapid desiccation hardening between the sexes. We speculate that sex differences in fuel use during desiccation may account for the discrepancy.     

Response of the Succulent Leaves of Peperomia magnoliaefolia to Dehydration: Water Relations and Solute Movement in Chlorenchyma and Hydrenchyma

Relative water content, solute concentrations, and osmolality were determined in the water storage tissue (hydrenchyma) and the assimilatory tissue (chlorenchyma) of the succulent leaves of Peperomia magnoliaefolia (Jac) (Piperaceae) during slow desiccation. Relative water loss was significantly greater for the hydrenchyma than for the chlorenchyma. When whole leaves had lost 50% of their initial water content, the concomitant decrease of the relative water content of the hydrenchyma was 75 to 85%, but of the chlorenchyma only 15 to 25%. In spite of this differential water loss, the osmolality in both tissues increased to the same extent, indicating solute flow from the hydrenchyma to the chlorenchyma during desiccation. Solute translocation appeared to be unspecific, probably reflecting symplastic mass flow from one tissue to the other. The observed volume preservation of the chlorenchyma stabilized photosynthesis of Peperomia magnoliaefolia (Jac) leaves, which was less inhibited by a given decrease of the relative water content of the whole leaves than in nonsucculent leaves.     

Developmental changes in the germinability, desiccation tolerance, hardseededness, and longevity of individual seeds of Trifolium ambiguum

Background and Aims

Using two parental clones of outcrossing Trifolium ambiguum as a potential model system, we examined how during seed development the maternal parent, number of seeds per pod, seed position within the pod, and pod position within the inflorescence influenced individual seed fresh weight, dry weight, water content, germinability, desiccation tolerance, hardseededness, and subsequent longevity of individual seeds.

Methods

Near simultaneous, manual reciprocal crosses were carried out between clonal lines for two experiments. Infructescences were harvested at intervals during seed development. Each individual seed was weighed and then used to determine dry weight or one of the physiological behaviour traits.

Key Results

Whilst population mass maturity was reached at 33–36 days after pollination (DAP), seed-to-seed variation in maximum seed dry weight, when it was achieved, and when maturation drying commenced, was considerable. Individual seeds acquired germinability between 14 and 44 DAP, desiccation tolerance between 30 and 40 DAP, and the capability to become hardseeded between 30 and 47 DAP. The time for viability to fall to 50 % (p₅₀) at 60 % relative humidity and 45 °C increased between 36 and 56 DAP, when the seed coats of most individuals had become dark orange, but declined thereafter. Individual seed f. wt at harvest did not correlate with air-dry storage survival period. Analysing survival data for cohorts of seeds reduced the standard deviation of the normal distribution of seed deaths in time, but no sub-population showed complete uniformity of survival period.

Conclusions

Variation in individual seed behaviours within a developing population is inherent and inevitable. In this outbreeder, there is significant variation in seed longevity which appears dependent on embryo genotype with little effect of maternal genotype or architectural factors.     

Subterranean termite open-air foraging and tolerance to desiccation: Comparative water relation of two sympatric Macrotermes spp. (Blattodea: Termitidae)

The foraging patterns of termites are strongly related to physiological limits in overcoming desiccation stress. In this study, we examined moisture preferences and physiological characteristics of Macrotermes carbonarius (Hagen) and M. gilvus (Hagen) as both exhibit conspicuous patterns of foraging activity. Despite both species showing no significant differences in calculated cuticular permeability, and percentage of total body water, they differed greatly in rate of water loss and surface area to volume ratio. For example, M. carbonarius which had a lower surface area to volume ratio (29.26-53.66) showed lower rate of water loss and percentage of total body water loss. This also resulted in higher LT₅₀ when exposed to extreme conditions (≈ 2% RH). However, contrasting observations were made in M. gilvus that has smaller size with higher surface area to volume ratio of 40.28-69.75. It is likely that the standard equation for calculating insect surface areas is inadequate for these termite species. The trend was further supported by the result of a moisture preference bioassay that indicated M. carbonarius had a broader range of moisture preference (between 5% and 20%) than M. gilvus which had a relatively narrow moisture preference (only 20%). These results explain why M. carbonarius can tolerate desiccation stress for a longer period foraging above-ground in the open air; while M. gilvus only forages below ground or concealed within foraging mud tubes.     

Body shape in terrestrial isopods: A morphological mechanism to resist desiccation?

Woodlice are fully terrestrial crustaceans and are known to be sensitive to water loss. Their half‐ellipsoidal shapes represent simple models in which to investigate theoretical assumptions about organism morphology and rates of exchange with the environment. We examine the influence of surface area and mass on the desiccation rates in three eco‐morphologically different species of woodlice: Oniscus asellus, Porcellio scaber, and Armadillidium vulgare. Our analysis indicates that the rate of water loss of an individual depends on both the initial weight and the body surface area. Interspecific and intraspecific analyses show that the mass‐specific water loss rate of a species decreases along with the ratio of surface area to volume. In particular, we show that body shape explains the difference in mass‐specific water loss rates between A. vulgare and P. scaber. This observation also explains several known ecological patterns, for example, the distribution and survivorship of individuals. However, in addition to body size and shape, water loss in terrestrial isopods depends also on the coefficient of permeability (i.e., a measure of water loss rate per surface unit), which is high in O. asellus and lower (and at similar levels) in P. scaber and A. vulgare. We discuss morphological, physiological, and behavioral aspects of water loss avoidance in terrestrial isopods. J. Morphol. 276:1283–1289, 2015. © 2015 Wiley Periodicals, Inc.     

Desiccation of intertidal limpets: Effects of shell size,fit to substratum,and shape

For undisturbed, field populations of the northeast Pacific, intertidal limpet Collisella pelta (Rathke), water loss was found to be proportional to apertural circumference rather than mantle cavity surface area. This contrasts with previous laboratory measurements for other limpet species and emphasizes the importance of the fit of shell to substratum for non-homing limpets. This close fit maintained a meniscus of water between the edge of the shell and the substratum, thereby reducing evaporative surface area and increasing the advantage of large size for reducing the rate of water loss. Shell-raising behavior eliminated the meniscus, increasing the rate of desiccation, and water loss appeared to become proportional to mantle cavity surface area. Indirect evidence suggests that C. pelta may utilize shell-raising behavior for evaporative cooling under thermally stressful conditions in the field.Both shell size and shape affect the ratio of water stores (proportional to internal shell volume) to evaporative surface area (proportional to apertural circumference) and per cent water loss is, potentially, a function of this ratio. Shape, however, (when defined as volume/circumference) exhibits an average allometric increase with increasing size (volume) for C. pelta, as well as for three other sympatric limpet species: C. Paradigitalis (Fritchman), C. Digitalis (Rathke), and Notoacmea scutum (Rathke). An independent measure of shape is, therefore, required to separate shape effects on desiccation from size effects; this measure was obtained by rearranging the allometry equation. In contrast to significant size effects, no measurable effect of shape on desiccation was detected. Variation in limpet shell shape may be partially or wholly maintained by factors other than an adaptational response to desiccation.     

Root desiccation and drought stress responses of bareroot Quercus rubra seedlings treated with a hydrophilic polymer root dip

Root hydrogel, a hydrophilic polymer, has been used to improve transplanting success of bareroot conifer seedlings through effects on water holding capacity. We examined mechanisms by which Terra-sorb® Fine Hydrogel reduces damage that occurs when roots of 1-year old, dormant northern red oak (Quercus rubra L.) were subjected to short-term (1, 3, and 5 h) pre-transplanting desiccation and long-term (45 days) drought stress following transplanting in a controlled environment chamber or greenhouse conditions. Hydrogel-treated seedlings had 80% greater root moisture content than non-root dipped control seedlings following the pre-transplanting desiccation period. Hydrogel reduced root membrane leakiness by 31% 5 h after the desiccation exposure. Hydrogel-treated seedlings did not show greater differences in shoot length, plant dry mass, root volume, net photosynthesis, and stomatal conductance compared with control seedlings following the 45-day drought stress exposure. A reduction in mean number of days to bud break in hydrogel-treated seedlings, combined with delayed tissue moisture loss (linked to higher stem water potential), suggests that hydrogel may have provided stress protection to aid survival under short-term desiccation, which may be beneficial toward alleviating initial transplanting stress.     

A comparison of water loss and gill areas in two supralittoral amphipods from New Zealand

Total gill area and gill distribution were measured for the sandhopper Talorchestia quoyana (Milne-Edwards) and the beach flea Transorchestia chiliensis (Milne-Edwards). For both species the gill structure and proportional area contributed by individual gills was similar. Gill 6 (G6) was the largest, providing 36% of the gill area in Tal. quoyana and 30% in Tr. chiliensis. The gill area/total dry weight relationships were similar, Y = 1.3 X^0.79 for Tal. quoyana and 1.4 X^0.78 for Tr. chiliensis. Small, medium and large amphipods survived >24 h in aerial conditions close to 100% RH at 15 °C. Rates of water loss in desiccating conditions increased with decreasing RH. Lethal water loss exceeded 30% weight loss for both species. Rate of water loss, (R) mg water loss. mg wet wt tissue. h^–1 exposed to 75% RH for Tr. chiliensis was 0.21, resulting in total mortality within 2 h. Medium Tal. quoyana were the most resistant group surviving 4 h exposure to 75% RH with R = 0.08. Differences in desiccation tolerances of the two amphipods are not explained by body water content, gill area relationships or the larger maximal size of T. quoyana. Results were combined with those from other talitrids to examine the relationship between gill area, water content, desiccation habitat and oxygen consumption in aerial and aquatic conditions. There were no consistent relationship between gill area, O₂ uptake and desiccation resistance. Amphipods show compensatory respiratory adaptation with individuals from all habitats, showing similar rates of oxygen uptake, either in air or in water, whichever was their most usual respiratory medium. Q¹⁰ values close to 2.0 were found in all ecomorphological groups. Sandhoppers, including Tal. quoyana, are best able to survive terrestrial conditions associated with a low humidity environment. It is concluded that the water loss characteristics of Tr. chiliensis limit its distribution on sand beaches to areas of high relative humidities.     

Water status and thermal analysis of alginate beads used in cryopreservation of plant germplasm

Encapsulation and dehydration techniques using alginate beads are used increasingly for the pre-treatment of various plant materials for cryopreservation to improve survival post-cryogenic storage. This study reports the effects of the water content of beads (formed with 3% (w/v) alginic acid in liquid S-RIB), polymerisation time (in 100 mM calcium chloride solution), osmotic dehydration (in 0.75 M sucrose solution), and evaporative air desiccation on the thermal properties of alginate beads used in cryopreservation protocols. Experimental beads were assayed using a differential scanning calorimeter (DSC) with a cooling programme to -150 degrees C, followed by re-warming. Resultant thermograms were evaluated with particular reference to the onset temperature and enthalpy of the melt endotherm from which the quantities of frozen and unfrozen water were calculated. Treatments were applied sequentially to samples of beads and their thermal features evaluated at each stage of the protocol. Using 'standard' beads (40-55 mg fresh weight), formed using plastic disposable pipettes, the degree of polymerisation (>10 min) proportionally reduced their dry weight and increased their water content. Thermal characteristics of the beads were unaffected by polymerisation times >10 min, but the maximum level (23%) of unfrozen (osmotically inactive) water was achieved after 15 min polymerisation. Osmotic dehydration using 0.75 M sucrose significantly lowered bead water content and mean dry weight approximately doubled with 20-24 h immersion time. Bead desiccation in still air reduced their water content by 83% of fresh weight, whilst dry weight remained constant. After 8 h desiccation in air between 27 and 37% of the water in the bead was osmotically inactive (unfrozen) in DSC scans. Desiccation >18 h reduced this fraction to zero. The melt onset temperature and the enthalpy of melting were directly related to bead water content. The unfrozen water fraction increased substantially with reduced water content of the beads (from 23 to 37% of total water content), concomitant with a reduction in the ratio of unfrozen to frozen water from 1:3 to 1:2. For successful vitrification and the production of a glass that did not destabilise on rewarming, a bead water content of ca. 26% of fresh weight (0.4 g waterg(-1) dry weight) was required, much of which was osmotically inactive water. These data are discussed in relation to optimal pre-treatments for alginate bead encapsulation techniques used in the cryopreservation of a range of plant germplasm. It is proposed that increased standardisation of alginate beads, in terms of volume, fresh weight, and water content, is required to reduce the variability in physical and thermal features, which in turn will improve survival of plant samples post-cryopreservation.     

Trade-off of energy metabolites as well as body color phenotypes for starvation and desiccation resistance in montane populations of Drosophila melanogaster

Storage of energy metabolites has been investigated in different sets of laboratory selected desiccation or starvation resistant lines but few studies have examined such changes in wild-caught populations of Drosophila melanogaster. In contrast to parallel selection of desiccation and starvation tolerance under laboratory selection experiments, opposite clines were observed in wild populations of D. melanogaster. If resistance to desiccation and starvation occurs in opposite directions under field conditions, we may expect a trade-off for energy metabolites but such correlated changes are largely unknown. We tested whether there is a trade-off for storage as well as actual utilization of carbohydrates (trehalose and glycogen), lipids and proteins in D. melanogaster populations collected from different altitudes (512-2500 m). For desiccation resistance, darker flies (> 50% body melanization) store more body water content and endure greater loss of water (higher dehydration tolerance) as compared to lighter flies (< 30% body melanization). Based on within population analysis, we found evidence for coadapted phenotypes i.e. darker flies store and actually utilize more carbohydrates to confer greater desiccation resistance. In contrast, higher starvation resistance in lighter flies is associated with storage and actual utilization of greater lipid amount. However, darker and lighter flies did not vary in the rate of utilization of carbohydrates under desiccation stress; and of lipids under starvation stress. Thus, we did not find support for the hypothesis that a lower rate of utilization of energy metabolites may contribute to greater stress resistance. Further, for increased desiccation resistance of darker flies, about two-third of total energy budget is provided by carbohydrates. By contrast, lighter flies derive about 66% of total energy content from lipids which sustain higher starvation tolerance. Our results support evolutionary trade-off for storage as well as utilization of energy metabolites for desiccation versus starvation resistance in D. melanogaster.