| Drought stress has profound adverse effects on plant growth and development, which results a significant decrease in yield. Therefore, great attentions have been paid to elucidate the mechanisms of plants to cope with the drought stress. One of the most important approaches towards this goal is to screen for and identify mutants that have defects in environmental stress response, and thus, dissect its molecular mechanism. In present study, two Arabidopsis null mutants of area and agb1-2 absent of the AtARCA and G proteins beta subunit and their wild type Col were used to investigate the possible molecular mechanisms of drought tolerance by comparing the phenotypic, physiological and biochemical differences among area, agb1 and Col under drought conditions. The major results are showed as followings:1. The sequence aligment results showed AtARCA and AGB1 had a high similarity abd identity. Furtheremore, both proteins displayed a similar three-dimensional structure.2. Atarca mutant and Col had a similar phenotype, which was different from that of agbl-2 mutant.3. A significant difference in drought tolerance was observed among three genotypes investigated. Atarca mutant showed the highest tolerant to soil drying among three genotypes. Water loss assay with the detached leaves indicated that wildtype Col lose water more rapidly than those of Atarca and agbl-2 mutants.4. The stomatal density and size (length) of leaves differed significantly among the three genotypes. Both mutants had a shorter stomatal length than that of wildtype, and the shortest stomatal length was observed for agbl-2 mutant. In contrast, both mutants had more stomata than that of the wild type, and agbl-2 mutant had the highest numbers of stomata. Signaificant differences in the response of stomata opening/closing to exogenous ABA treatment were also observed among three genotypes investigated. Both mutants showed more sensitive to ABA treatment than that of wild type, and theAtrackl showed the most sensitive to ABA treatment.5. Under soil drying condition, the leaf water potential of all three genotypes decreased gradually with the progress of soil drying. However, the leaf water potential of arca and agb1-2 mutants was always higher than that of Col. A significant difference in stomatal diffusion resistance was observed among the three genotypes in responses to soil drying and both mutants displayed higher stomatal diffusion resistance than that of the wild type. The ABA content of both leaves and roots showed a similar change as those of stomatal diffusion resistance. Similar results were also observed when seedlings (cultured in the hydroponic solution) were exposed to 4% PEG60006. The growth of both the primary roots and the secondary roots of the seedlings of three genotypes was influenced by the treatment with exogenous ABA, PEG and fluridone, an inbitor of ABA biosynthesis. The effects of ABA and PEG treatments on root growth of Atarca mutant were less than those of agb1-2 mutant and Col.According to the above results and other reports, it was suggested that both AtARCA and AtAGB1 played an important role in drought tolerance and both proteins might involve in the signal transduction of drought stress, but their mechanisms were different. |
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