ABA-induced tolerance to ion leakage during rehydration following desiccation in the moss Atrichum androgynum

A simple ion leakage assay was used to investigate the effect ofabscisic acid (ABA) pretreatment on desiccation tolerance in the mossAtrichum androgynum. Results from experiments involvingtheapplication of the protein synthesis inhibitor cyclohexamide during desiccationor rehydration suggested that pretreatment with ABA does not facilitate theproduction of protection or repair proteins duringdesiccation or rehydration. Rather, ABA induces the synthesis of these proteinsduring pretreatment. The ABA-induced increase in tolerance was much less ifplants were pretreated in the dark. Exposure to red light could not substitutefor white light, suggesting that ABA action does not require phytochrome.Desiccating intact long stem segments or long segments separated into apicalandbasal parts had no effect on the desiccation tolerance of either plant part.This suggests that no movement of signals or protective molecules occurs fromthe stem bases to the apices during desiccation. Basal stem segments were muchmore sensitive to desiccation than apical regions, suggesting during senescencea breakdown in mechanisms that protect mosses from injury occurs. Theimplications of these findings for the water relations of A.androgynum are discussed.     

Responses of Photosynthesis and Biomass Allocation of an Understorey Herb, Pteridophyllum racemosum, to Gradual Increases in Irradiance

In wave-regenerating Abies forests in central Japan, light availabilityon the forest floor of a mature-tree stand increases graduallyover 4 to 5 years during the senescence of trees. The understoreyevergreen perennialPteridophyllum racemosum Sieb. et Zucc. (Papaveraceae)is commonly found in such forests. To determine the acclimationcharacteristics of this species to gradual changes in lightavailability, leaf photosynthetic traits and biomass allocationpatterns were determined along a transect running from fullyshaded understorey to a canopy gap. Along the transect, thephoton flux density on the forest floor relative to full sun(RPFD) varied from 2.3–36.7%. The light-saturated netphotosynthetic rate of field-grown plants increased as the lightenvironment increased from 2.3–14.1% RPFD. However, aslight conditions increased from moderate (14.1%) to high (36.7%),the light-saturated net photosynthetic rate decreased to a levelcomparable to that exhibited by low-light grown plants. On theother hand, root mass per unit leaf area (RMA) increased withincreasing light conditions. A higher RMA contributes to a higherwater uptake capacity per unit leaf area which in turn supportshigher rates of photosynthesis and transpiration in high light.We conclude that in wave-regenerating forests P. racemosum cansurvive in high-light environments by avoiding a severe waterdeficit and heat load by increasing RMA. Copyright 2001 Annalsof Botany Company Biomass allocation, photosynthesis, Pteridophyllum racemosum, root mass per unit leaf area, wave regeneration     

An ATP Binding Cassette Transporter Is Required for Cuticular Wax Deposition and Desiccation Tolerance in the Moss Physcomitrella patens

The plant cuticle is thought to be a critical evolutionary adaptation that allowed the first plants to colonize land, because of its key roles in regulating plant water status and providing protection from biotic and abiotic stresses. Much has been learned about cuticle composition and structure through genetic and biochemical studies of angiosperms, as well as underlying genetic pathways, but little is known about the cuticles of early diverging plant lineages. Here, we demonstrate that the moss Physcomitrella patens, an extant relative of the earliest terrestrial plants, has a cuticle that is analogous in both structure and chemical composition to those of angiosperms. To test whether the underlying cuticle biosynthetic pathways were also shared among distant plant lineages, we generated a genetic knockout of the moss ATP binding cassette subfamily G (ABCG) transporter Pp-ABCG7, a putative ortholog of Arabidopsis thaliana ABCG transporters involved in cuticle precursor trafficking. We show that this mutant is severely deficient in cuticular wax accumulation and has a reduced tolerance of desiccation stress compared with the wild type. This work provides evidence that the cuticle was an adaptive feature present in the first terrestrial plants and that the genes involved in their formation have been functionally conserved for over 450 million years.     

苔藓植物耐旱机制研究进展

耐旱藓类快速脱水并存活的能力可由快速建立起来的对环境变化的耐受机制来反映,保护细胞完整性的组成型机制与修复细胞损伤的诱导机制协同作用使苔藓植物渡过干旱胁迫.再水化时光合系统原初恢复非常迅速;ABA处理可显著改变PSⅡ的生理特征;基因表达的变化主要由翻译调控引起;脱水组织中贮存mRNPs既保护了mRNAs,又加快了再水化修复速度.山墙藓(Tortula ruralis)是耐旱研究较多的一个种,已建立了表达序列文库(EST),将会成为耐旱研究的重要模式植物.     

Increased activities of superoxide dismutase and catalase are not the mechanism of desiccation tolerance induced by hardening in the moss Atrichum androgynum

Abstract

The effects of treatments that increase desiccation tolerance were tested on the activity of the enzymes superoxide dismutase (SOD) and catalase (CAT) in the moss Atrichum androgynum subjected to a drying/wetting cycle. Hardening by both abscisic acid (ABA) pretreatment and partial dehydration significantly increased the rate of recovery of photosynthesis during rehydration following desiccation. Hardening treatments had little effect on SOD activity. In non-hardened plants, SOD activity increased three-fold during desiccation for 32 h at 52% rh, but hardened material tended to display smaller increases in activity. During rehydration, SOD activities rapidly declined to their initial values in all treatments. Hardening by partial dehydration, but not ABA, reduced CAT activity. After desiccation for 32 h, material from all treatments displayed about half the initial CAT activity, and activity did not change during subsequent rehydration. Results show that, while the induction of SOD appears to play a role in desiccation tolerance, a similar induction occurred in both hardened and non-hardened mosses. Induction of greater activities of enzymes that scavenge reactive oxygen species is not responsible for the added tolerance induced by hardening treatments.     

Engineering Desiccation Tolerance in Escherichia coli

Recombinant sucrose-6-phosphate synthase (SpsA) was synthesized in Escherichia coli BL21DE3 by using the spsA gene of the cyanobacterium Synechocystis sp. strain PCC 6803. Transformants exhibited a 10,000-fold increase in survival compared to wild-type cells following either freeze-drying, air drying, or desiccation over phosphorus pentoxide. The phase transition temperatures and vibration frequencies (PO stretch) in phospholipids suggested that sucrose maintained membrane fluidity during cell dehydration.     

The Conservation of Polyribosomes in the Moss Tortula ruralis during Total Desiccation

Total desiccation of the moss Tortula ruralis was achieved byplacing it in a dry atmosphere for 90 min. Reintroduction ofthe moss to water resulted in the recovery of its normal morphologicalform within 15–30 s. The sedimentation profile on a sucrosegradient of the ribosomal content of the totally dry moss showsthe presence of distinct polyribosomal peaks. The levels ofthese polyribosomes rise upon rehydration of the moss. The differencebetween the tolerance to water deficit by this moss and by higherplants is outlined.     

Polyribosomes Conserved during Desiccation of the Moss Tortula ruralis Are Active

During desiccation of the moss Tortula ruralis (Hedw.) (Gaertn, Meyer and Scherb) polyribosomes are conserved. On rehydration, protein synthesis is rapidly resumed. In the presence of protein synthesis initiation inhibitors ribosome run-off from the conserved polyribosomes takes place, confirming that these retain their activity as intact structures during desiccation.     

Abscisic Acid and Desiccation Tolerance in Mosses

In higher plants the phytohormone ABA is involved in processes that are connected to water deficit, like stomatal closure or desiccation tolerance. In bryophytes, also containing ABA in their tissues, physiological functions remained uncertain for a long time. Quite recently, several papers have shown different effects of exogenously applied ABA: stomatal closure in Anthoceros, drought hardening in Funaria and production of the landform in Riccia. In all these cases the relevant conditions (water deficit) enhance the endogenous ABA level significantly. For induced desiccation tolerance, ABA serves as a mediator to induce specific proteins (dehydrins) strongly connected with this tolerance. Therefore, it can be concluded that in bryophytes ABA has the same function as in higher plants. It acts as a mediator in stress conditions.     

Desiccation Tolerance Studied in the Resurrection Plant Craterostigma plantagineum

This review will focus on the acquisition of desiccation tolerancein the resurrection plant Craterostigma plantagineum. Molecularaspects of desiccation tolerance in this plant will be comparedwith the response of non-tolerant plants to dehydration. Uniquefeatures of C. plantagineum are described like the CDT-1 (Craterostigmadesiccation tolerance gene-1) gene and the carbohydrate metabolism.Abundant proteins which are associated with the desiccationtolerance phenomenon are the late embryogenesis abundant (=LEA)proteins. These proteins are very hydrophilic and occur in severalother species which have acquired desiccation tolerance.     

Influence of Protoplasmic Water Loss on the Control of Protein Synthesis in the Desiccation-Tolerant Moss Tortula ruralis: Ramifications for a Repair-Based Mechanism of Desiccation Tolerance

Desiccation tolerance of the moss Tortula ruralis is characterized by a desiccation-induced change in gene expression that becomes evident upon rehydration. As reported earlier, this change in gene expression is apparently brought about by a change in the control of translation and does not include a major shift in mRNA abundance. A full qualitative and quantitative analysis of the alteration in gene expression, which is characterized by the loss of (or greater than fivefold decrease in) the synthesis of 25 hydration (h) proteins and initiation (or greater than fivefold increase) of the synthesis of 74 rehydration (r) proteins, is given in this report. Exposure to a desiccating atmosphere, for times that result in varying levels of water loss, enabled the determination that the control of synthesis of r proteins is different from the control of synthesis of h proteins. The r and h protein synthesis responses are internally coordinate, however. Similarly, the return to normal levels of h protein synthesis differs from that of the r proteins. The return to normal synthetic levels for all h proteins is synchronous, but the rate of loss of r protein synthesis varies with each individual r protein. Run-off translation of polysomes isolated from gametophytes during the drying phase demonstrates that there are no novel mRNAs recruited and no particular mRNA is favored for translation during desiccation. These findings add credence to the argument that translational control is the major component of the desiccation-induced alteration in gene expression in this plant, as discussed. Aspects of the response of protein synthesis to desiccation are consistent with the hypothesis that T. ruralis exhibits a repair-based mechanism of desiccation tolerance.     

沙芥种子发育过程中的脱水耐性

以发育过程中经脱水和未脱水处理的沙芥种子为试验材料,测定了其含水量、萌发率和抗氧化酶系统,探讨了沙芥种子脱水耐性与抗氧化系统之间的关系。结果表明：在20～60DAF,沙芥种子含水量逐渐下降,干重逐渐增加;60DAF种子具有萌发能力,萌发率为24％;且脱水可促进沙芥种子的萌发,人工脱水至含水量为12％和5％时,萌发率分别为56％和44％,自然脱水至含水量为12％和5％时,萌发率分别为52％和60％;发育过程中沙芥种子SOD活性逐渐降低,而CAT、POD、LOX活性以及MDA含量均呈上升趋势;在脱水过程中,随着种子含水量的下降SOD活性逐渐降低,CAT和LOX活性逐渐升高,而POD活性呈先降低后升高的变化趋势。脱水后,种子中MDA含量均高于CK。60DAF的沙芥种子已获得脱水耐性。     

ABA treatment increases both the desiccation tolerance of photosynthesis,and nonphotochemical quenching in the moss Atrichum undulatum

Pulse amplitude modulation fluorescence was used to investigate whether abscisic acid (ABA) pretreatment increases the desiccation tolerance of photosynthesis in the moss Atrichum undulatum. In unstressed plants, ABA pretreatment decreased the F _V/F _m ratio, largely as a result of an increase in F _o. This indicated a reduction in energy transfer between LHCII and PSII, possibly hardening the moss to subsequent stress by reducing the production of the reactive oxygen species near PSII. During desiccation, F ₀, F _m, F _v/F _m, PSII, and NPQ and F ₀ quenching declined in ABA-treated and nontreated mosses. However, during rehydration, F ₀, F _m, F _v/F _m, and PSII recovered faster in ABA-treated plants, suggesting that ABA improved the tolerance of photosystem II to desiccation. NPQ increased upon rehydration in mosses from both treatments, but much more rapidly in ABA-treated plants; during the first hour of rehydration, NPQ was two-fold greater in plants treated with ABA. F ₀quenching followed a similar pattern, indicating that ABA treatment stimulated zeaxanthin-based quenching. The implications of these results for the mechanisms of ABA-induced desiccation tolerance in A. undulatum are discussed.     

ABA与植物的耐盐性

文章介绍近年来ABA与植物耐盐性的研究进展。     

Reversible Inactivation and Desiccation Tolerance of Silicified Viruses

Long-distance host-independent virus dispersal is poorly understood, especially for viruses found in isolated ecosystems. To demonstrate a possible dispersal mechanism, we show that bacteriophage T4, archaeal virus Sulfolobus spindle-shaped virus Kamchatka, and vaccinia virus are reversibly inactivated by mineralization in silica under conditions similar to volcanic hot springs. In contrast, bacteriophage PRD1 is not silicified. Moreover, silicification provides viruses with remarkable desiccation resistance, which could allow extensive aerial dispersal.     

Heat-stable Proteins and Acquisition of Desiccation Tolerance in Peanut Seeds

The acquisition and induction of desiccation tolerance associated with the expression of heat-stable proteins in the developing peanut (Arachis hypogaea L. ) seeds were studied. Desiccation tolerance of peanut seeds was achieved during 45 to 65 DAP (days after pegging) embryogenesis, while a set of low molecular weight (9 to 15.5 kD) heat-stable polypeptides was preferentially expressed. Slow drying regime applied in vitro to 25 and 35 DAP peanut embryos induced desiccation tolerance and the expression of the same subset of polypeptides. Mature drying treatment enhanced the ability of 65 DAP peanut embryos to withstand fast drying, also increased the heat stability of arachins, the major peanut storage protein, which was heat labile during 45 to 65 DAP embryogenesis. It was concluded that the heat-stable proteins may contribute to desiccation tolerance of the peanut seeds, and the low molecular weight heat-stable polypeptides may confer nonspecifieally heat tolerance on peanut storage proteins which were normally heat labile.