Desiccation tolerance in Physcomitrella patens: Rate of dehydration and the involvement of endogenous abscisic acid (ABA)

The moss Physcomitrella patens , a model system for basal land plants, tolerates several abiotic stresses, including dehydration. We previously reported that Physcomitrella patens survives equilibrium dehydration to ?13 MPa in a closed system at 91% RH. Tolerance of desiccation to water potentials below ?100 MPa was only achieved by pretreatment with exogenous abscisic acid (ABA). We report here that gametophores, but not protonemata, can survive desiccation below ?100 MPa after a gradual drying regime in an open system, without exogenous ABA. In contrast, faster equilibrium drying at 90% RH for 3–5 days did not induce desiccation tolerance in either tissue. Endogenous ABA accumulated in protonemata and gametophores under both drying regimes, so did not correlate directly with desiccation tolerance. Gametophores of a Ppabi3a/b/c triple knock out transgenic line also survived the gradual dehydration regime, despite impaired ABA signaling. Our results suggest that the initial drying rate, and not the amount of endogenous ABA, may be critical in the acquisition of desiccation tolerance. Results from this work will provide insight into ongoing studies to uncover the role of ABA in the dehydration response and the underlying mechanisms of desiccation tolerance in this bryophyte.     

Novel Drought-Inducible Genes in the Highly Drought-Tolerant Cowpea: Cloning of cDNAs and Analysis of the Expression of the Corresponding Genes

Ten cDNAs of genes that were induced by dehydration stress werecloned by differential screening from the highly drought-tolerantlegume, cowpea (Vigna unguiculata), a major crop in West Africa.The clones were collectively named CPRD (cowpea clones responsiveto dehydration). Northern blot analysis revealed that nine ofthe CPRD genes were induced by dehydration stress, but the timingof induction of mRNA synthesis varied among the CPRD genes.We analyzed the effects of other environmental stresses on theexpression of the CPRD8, CPRD14 and CPRD22 genes, and we foundthat these genes were strongly induced by high-salinity stressbut not by cold or heat stress. Drought-stressed cowpea plantsaccumulated abscisic acid (ABA) to a level that was 160 timeshigher than that in unstressed plants. The CPRD8 and CPRD22genes were induced to a significant extent by the applicationof exogenous ABA but the CPRD14 gene was not. These resultsindicate the existence of at least two signal-transduction pathwaysbetween the detection of water stress and the expression ofCPRD genes in cowpea. Sequence analysis of CPRD8 and CPRD22cDNAs revealed that they encoded putative proteins that wererelated to old yellow enzyme and group 2 LEA proteins, respectively.The protein encoded by CPRD14 exhibited sequence homology todihydroflavonol-4-reductase (DFR) and vestitone reductase (VR).Old yellow enzyme, DFR and VR have not been identified as drought-inducibleproteins in other plants, whereas LEA genes have been well characterizedas drought-inducible genes. The various gene products mightfunction to protect cells from environmental stress. (Received April 17, 1996; Accepted August 28, 1996)     

Expression of three ABA-regulated clones and their relationship to maturation processes during the embryogenesis of chick-pea seeds

Water stress inhibits germination of chick-pea seeds and produces specific changes in gene expression. some of which are coincident with those induced by the exogenous application of abscisic acid (ABA). Three cDNA clones, GAB-8, GAB-9 and GAB-11, were previously identified as under the regulation of ABA and osmotic stress in embryonic axes of germinating chick-pea. Here we try to establish a relationship between the changes in gene expression induced by ABA and stress conditions during germination and those naturally occurring during the desiccation process that leads to seed maturation. Our results show that the germinative capacity of chick-pea is related to the water content of the organ. In vitro translation of the mRNAs from developing seed reveals that in the later stages of seed maturation some polypeptides appear that previously were found to be regulated by ABA and by water deficit in germinating seeds. Hybridization by northern blot of embryogenic mRNAs with GAB-8. GAB-9 and GAB-11 clones shows that the mRNAs corresponding to such clones only appear in the later phases of seed formation, coinciding with seed dehydration, and persisting until seeds became fully mature. The results suggest that these mRNAs are probably related to the response to dehydration that occurs during seed maturation, and that the pattern of expression of these ABA-regulated clones coincides with that of the established late embryogenesis-abundant (LEA) genes.     

The pepper late embryogenesis abundant protein CaLEA1 acts in regulating abscisic acid signaling,drought and salt stress response

As sessile organisms, plants are constantly challenged by environmental stresses, including drought and high salinity. Among the various abiotic stresses, osmotic stress is one of the most important factors for growth and significantly reduces crop productivity in agriculture. Here, we report a function of the CaLEA1 protein in the defense responses of plants to osmotic stress. Our analyses showed that the CaLEA1 gene was strongly induced in pepper leaves exposed to drought and increased salinity. Furthermore, we determined that the CaLEA1 protein has a late embryogenesis abundant (LEA)_3 homolog domain highly conserved among other known group 5 LEA proteins and is localized in the processing body. We generated CaLEA1‐silenced peppers and CaLEA1‐overexpressing (OX) transgenic Arabidopsis plants to evaluate their responses to dehydration and high salinity. Virus‐induced gene silencing of CaLEA1 in pepper plants conferred enhanced sensitivity to drought and salt stresses, which was accompanied by high levels of lipid peroxidation in dehydrated and NaCl‐treated leaves. CaLEA1‐OX plants exhibited enhanced sensitivity to abscisic acid (ABA) during seed germination and in the seedling stage; furthermore, these plants were more tolerant to drought and salt stress than the wild‐type plants because of enhanced stomatal closure and increased expression of stress‐responsive genes. Collectively, our data suggest that CaLEA1 positively regulates drought and salinity tolerance through ABA‐mediated cell signaling.     

35S::GmPM30在拟南芥的根系生长中表现为对ABA的敏感性降低(英文)

LEA protein,late-embryogenesis-abundant protein,is importantin response to thesalt and drought stresses in plants.Here,weidentified a cDNA full length of LEA from soybean and found that LEA enhance the ability of anti-salinity in transgenic Arabidopsis thaliana.The expression of GmPM30 increases highly under salinity,cold or ABA treatment,and enhances by certain degree under drought stress.The germination rates,primary root lengths and survival rate of GmPM30 over-expression lines are obviously higher than that of the wild-type after suffering the salinity stress.Our studies displays that GmPM30-ox apparently enhances the tolerance to salinity in Arabidopsis thaliana.     

Antioxidant response and Lea genes expression under exogenous ABA and water deficit stress in wheat cultivars contrasting in drought tolerance

Two wheat (Triticum aestivum) cultivars, C306 (drought tolerant) and PBW343 (drought susceptible) were compared for their response to exogenous ABA, water stress (WS) and combined (ABA plus WS) during their seedlings growth. Their responses were studied in the form of seedlings growth, antioxidant potential of roots and shoots and expression levels of LEA genes in shoots. ABA treatment led to increase in levels of ascorbate, ascorbate to dehydroascorbate ratio, antioxidant enzymes and decreases in levels of dehydroascorbate, malondialdehyde (MDA). Decrease in biomass, ascorbate contents, ascorbate to dehydroascorbate ratios and antioxidant enzymes was more in PBW343 than in C306 under WS. Dehydroascorbate and MDA levels were higher in PBW343 than in C306 under WS. ABA plus WS improved some of these features from their levels under WS in PBW343. Proline contents were not increased significantly under ABA in both cultivars. Out of ten LEA genes studied, six LEA genes were induced more under WS than under ABA in C306 but equally induced in PBW343. Four LEA genes were induced earlier in PBW343 but later in C306. Wdhn13 was induced more under ABA than under WS in C306 while it was non-responsive to both stresses in PBW343.     

Genotypic Variability in Differential Expression of lea2 and lea3 Genes and Proteins in Response to Salinity Stress in Fingermillet (Eleusine coracanaGaertn) and Rice (Oryza sativaL.) Seedlings

Some late embryogeny abundant (LEA) proteins, which are developmentallyregulated in embryos, are also known to be expressed in meophytictissues in response to osmotic stress. Here we report the extentof genetic variability in the level of expression of lea2 andlea3, under stress, in fingermillet and rice seedlings. In bothspecies, the expression of lea genes was seen in the mesophytictissue in response to salinity, partial dehydration and abscisicacid. Tolerant genotypes exhibited higher expression of rab16Aand M3 that code for LEA2 proteins, than susceptible genotypes.A novel approach, that of raising antibodies against the conservedpeptides of these proteins was used to study genetic variabilityin LEA protein levels. Since stress proteins are known to beexpressed in response to mild, non-lethal induction-stress (Uma,Prasad and Udayakumar,Annals of Botany76: 43–49, 1995),we developed an optimum induction protocol for salinity stressin rice and fingermillet. We studied the quantitative differencesin expression of these proteins by western blot and ELISA techniquesin different genotypes. A positive correlation was found betweenLEA2 and LEA3 protein levels and the growth of seedlings duringstress and recovery in both rice and fingermillet, indicatinga possible relevance of these proteins in stress tolerance.Copyright1998 Annals of Botany Company LEA proteins, ABA responsive proteins, induction response, ELISA, fingermillet, rice, salinity-stress.