Desiccation-sensitive Species Research Articles

Changes in in vivo Protein Complements in Drying Leaves of the Desiccation-Tolerant Grass Sporobolus stapfianus and the Desiccation-Sensitive Grass Sporobolus pyramidalis

Protein synthesis in vivo was studied with two-dimensional SDS-PAGE of extracts of leaves on intact drying plants of Sporobolus stapfianus (a desiccation-tolerant grass) and S. pyramidalis (a desiccation-sensitive species). Protein complements were also studied in dried, detached leaves of S. stapfianus (detached leaves are also desiccation-sensitive). Extensive changes in in vivo proteins were observed in S. stapfianus plants drying intact: 25 novel proteins, 10 proteins augmented, 13 proteins decreased and 7 proteins disappeared. Two main phases could be distinguished in leaves as plants dry. In the first phase (85-51% relative water content (RWC) range), 10 novel proteins appeared and 2 proteins increased in content. In the second phase (37-3.5% RWC), 15 novel proteins appeared and 2 proteins increased in content. Some changes in protein patterns were also observed in desiccation- sensitive leaves, i.e. in (a) S. stapfianus leaves drying detached and in (b) drying S. pyramidalis leaves attached. These changes were fewer than those in desiccation-tolerant leaves, i.e. in (c) S. stapfianus leaves drying on intact plants; that is, (a) and (b) differed from each other and from (c), which indicates that there is no common injury-related pattern of protein change. These results are consistent with the view that changes in protein complements accompany the induction of desiccation tolerance in drying plants of S. stapfianus.

944 COLD-STORAGE TREATMENTS AFFECT WATER RELATIONS OF BARE-ROOT TREES

Shoot and root water potentials were determined for bare-root Norway maple (Acer platanoides L.) and washington hawthorn (Crataegus phaenopyrum Med.) seedlings subjected to shoot and root exposure treatments for six cold storage durations. Shoot and root water potentials for all exposure treatments and both species decreased with increased time in storage, and the greatest degree of water stress occurred during the first six weeks of storage. Maple shoot and root water potentials for the exposed shoot treatment were the same as the whole plant covered treatment. In contrast, hawthorn shoot and root water potentials for the exposed shoot treatment were the same as values for the roots exposed treatment. Based on these data, we conclude that desiccation sensitive species such as washington hawthorn require root and shoot protection to minimize water loss.

Mist Irrigation Reduces Post-transplant Desiccation of Bare-root Trees

Abstract Desiccation during storage and reestablishment is a major factor contributing to poor regrowth of transplanted bare-root trees. The effect of overhead mist irrigation on reducing post transplant water stress in Norway maple (Acer platanoides L. ‘Emerald Lustre’) and Yoshino cherry (Prunus x yedoensis) was examined. Bare-root Norway maple (desiccation tolerant) and Yoshino cherry (desiccation sensitive) trees were transplanted into pine bark-filled containers and subjected to mist or non-mist treatments. Stem xylem water potential, relative water content, and survivability were determined. Xylem water potential increased (became less negative) for misted maple and cherry trees. Water potential increased for non-misted maple and decreased for non-misted cherry trees. Twenty-seven percent of non-misted cherries were evaluated as nonmarketable due to stem dieback compared to 0% for misted trees. Results of this study indicate that mist irrigation effectively reduces desiccation damage for desiccation sensitive species such as cherries and hawthorns.

The relationship between carbohydrate composition of some tree seeds and their longevity

Fresh mature tree seeds of 16 species plus soybean were used for the analysis of soluble neutral sugar content, as well as for the determination of longevity in terms of the time required for the seeds to decrease to 50% of the original germination under 5 o C and 80-91% relative humidity. Oligosaccharides were sometimes found in species of recalcitrant; although the mass ratio of oligosaccharide/total sugar or mole ratio of stachyose and raffinose/sucrose was less than 0.05 or 0.044, respectively. The time required for seeds to decrease to 50% germination varied from a few days to 8.3 months for the seeds of desiccation-sensitive species. The low ratio of oligosaccharide to sucrose is, however, most unlikely to be a cause of short life-span in recalcitrant seeds

Radical formation and accumulation in vivo, in desiccation tolerant and intolerant mosses.

Water loss in a desiccation-sensitive moss resulted in destruction of chlorophyll, loss of carotenoids and increased lipid peroxidation, indicating the presence of damaging forms of activated oxygen. These effects were exaggerated when the plants were desiccated at high light intensities. During water-deprivation there was a build up of a free radical, detected in vivo, with a close correlation between molecular damage and radical accumulation. In contrast, in a desiccation-tolerant moss there was almost no indication of molecular (oxidative) damage. However a stable radical similar in type and concentration to that found in the desiccation-sensitive species accumulated, particularly under high irradiances. The stable radical appears to be one of the end-products of a process initiated by environmental stress, desiccation and high irradiance: its association with molecular damage depending on the degree to which the species is tolerant of desiccation. Identification of the radical in intact tissue from EPR and ENDOR studies, suggests that this is not a short-lived peroxy-radical but instead is relatively stable and carbon-centred.

Salinity studies with drought-resistant species of Sporobolus.

Dry matter productivity under saline conditions was compared in 5 desiccation-tolerant "resurrection" grasses and one desiccation sensitive species, all in the genus Sporobolus. S. stapfianus was the most salt tolerant, requiring 215 mole NaCl m-3 to reduce shoot dry matter increments to 50% of increments in plants not treated with salt. (This was comparable to published values for the salt tolerant grass Diplachne fusca.) S. lampranthus was salt sensitive, requiring 35 mol m-3 for 50% control yields. S. festivus, S. aff. Fimbriatus, and the deisccation sensitive S.pyramidalis was moderately tolerant (150-170 mol m-3). The moderate salt resistance of S. aff. fimbriatus was attributed mainly to exclusion of NaCl by roots. Salt export through leaf surfaces was a minor factor. Half of the leaf mesophyll cells survived 50 min immersion in 200 mol NaCl m-3. Plants of S. aff. fimbriatus and S. pyramidalis tolerated a broad range of soil pH. Plants of 4 desiccation tolerant Sporobolus species survived air-dryness following 3 weeks pretreatment with salinities up to 200 mol m-3.

Electrofusion of Protoplasts from Desiccation Tolerant Species and Desiccation Sensitive Species of Grasses

Protoplasts were prepared (by enzymatic degradation of the cell wall), from desiccation tolerant “resurrection grasses” in the genera Eragrostis and Sporobolus and from desiccation sensitive grasses in these same genera. The technique of electrofusion was applied successfully to achieve fusion of leaf protoplasts from desiccation tolerant plants with those from sensitive plants in different combinations involving 5 species. Protoplasts from 2 species of desiccation tolerant grasses were also fused.

Disturbance histories of four snowdonian woodlands and their relation to Atlantic bryophyte distributions

Small deciduous woods in the mountains of North Wales may be relicts of ancient woodland, but centuries of intensive land use mean it is very unlikely that any are completely unmodified or undisturbed. Some woods are characterised by the presence of desiccation-sensitive atlantic bryophytes, which could possibly serve as indicators of the least disturbed sites. Studies of atlantic bryophyte distributions, and historical reconstructions based on pollen analyses, stand demography, and documentary records for four woods (two rich and two poor in atlantic bryophytes) revealed the following: 1. (1) At least some part of each wood had suffered disturbances during the past 300 years, including coppicing, clear felling, and grazing. 2. (2) Richness and abundance of atlantic bryophyte communities were largely correlated with availability of habitats, i.e., rocks with permanent moisture, shelter, and favourable substrate. Habitats varied in quality and quantity within and between woods. 3. (3).Where disturbance involved an extended period with an open or absent canopy, atlantic bryophytes occur in abundance only in extremely moist and shaded locations. Where disturbance was followed by rapid canopy regrowth, their distributions are not so restricted. No clear-cut relationship exists between the occurrence of rare atlantic bryophytes and disturbance histories. The persistence of desiccation-sensitive species depends on the quality of available habitats, as well as the nature of woodland disturbances. Woods richest in rare atlantic species have supported some continuous tree canopy over the last 1200 years or contain an abundance of moist, shaded habitats. The international importance of atlantic bryophytes and their future conservation is discussed.

Sulphydryl and Disulphide Levels in Protein Fractions from Hydrated and Dry Leaves of Resurrection Plants

Significant changes in sulphydryl ('SH') and disulphide CSS') levels during air-drying in leaves of * resurrection' plants (whose protoplasm survives dehydration) stemmed mainly from protein turnover effects. No significant changes were found in the SH, SS levels in leaves of the desiccation sensitive species Sporobolus pyramidalis following air-drying. The three tolerant species studied differed in the direction of change. Some data were consistent with Levitt's SH, SS hypothesis: increases in protein-SS levels in Sporobolus stapfianus (desiccation tolerant) were consistent with a stabilization of new protein by SS bonds; lower reactivity of protein-SH in the tolerant species Talbotia elegans (which on the other hand has decreased protein-SS) is consistent- with a second mechanism of decreasing protein denaturation proposed in Levitt's hypothesis. Evidence of some conversion of SH to SS in the soluble proteins of Xerophyta viscosa (a tolerant species) would on Levitt's hypothesis indicate an injurious process. Some degree of protein denaturation might be indicated by partial inactivation of the soluble enzyme ribulose bisphosphate carboxylase in this species, and loss of some soluble isoenzymes (peroxidase and alkaline phosphatase). An apparent lack of SH conversion to SS in the sensitive species Sporobolus pyramidalis was not consistent with the SH, SS hypothesis.

Dessication-induced Changes in the Protein Complement of Soluble Extracts from Leaves of Resurrection Plants and Related Desiccation-sensitive Species

Dessication-induced Changes in the Protein Complement of Soluble Extracts from Leaves of Resurrection Plants and Related Desiccation-sensitive Species

The effect of dehydration and rehydration on the nitrogen content of various fractions from resurrection plants

Nitrogen contents were determined in 20 species of “resurrection plants”,i.e. plants with leaves which are able to revive from an air-dry state (viz. Boea hygroscopica, Borya nitida, Cheilanthes sieberi, Coleochloa pallidior, C. setifera, Craterostigma plantagineum, Myrothamnus flabellifolia, Oropetium capense, Pellaea calomelanos, P. falcata, P, viridis, Polypodium polypodioides, Ramondia pyrenaica, Selaginella lepidophylla, Sporobolus stapfianus, Talbotia elegans,Tripogon loliiformis, Xerophyta retinervis, X. villosa, X. viscosa), and in three desiccation sensitive species (Eragrostis tenuifolia, Selaginella kraussiana andSporobolus pyramidalis).In a preponderance of resurrection plants insoluble nitrogen content fell during dehydration of intact plants and soluble non-protein N rose. Both changes were particularly marked in species which lose chlorophyll and thylakoid structure during drying. These trends were usually only partially reversed after 24 h rehydration. Recovery of14C-leucine incorporation in rehydrating leaves was slow.Leaves of desiccation sensitive vascular plants tended on the average to lose soluble protein rather than insoluble N during drying, and tended to have higher soluble non-protein N contents than tolerant plants.However, similarity in the changes in N-contents inXerophyta villosa leaves killed by airdrying compared to leaves surviving air-drying, opposes the view that death was due to excessive loss of protein.