Athk1 And Gpa1 Genes In Peg Induced Proline And The Role Of Abscisic Acid Synthesis And The Effect Of Light

Plant cells can rapidly biosynthesize and accumulate abscisic acid (ABA) and proline upon exposing to a variety of abiotic stresses, which is considered to play important roles in plant stress response. In this study, the ATHK1null mutant, G protein a subunit null mutant and their wildtype are used to investigate the mechanisms of PEG induced ABA and proline accumulation and the roles ATHK1and GPA1played in such processes. The main results are summrized as follows:1. The content of proline and ABA of different genotypes of Arabidopsis seedlings increased significantly after PEG treatment. However, as compared to the wildtypes, the content of proline and ABA of athkl seedlings were much lower than that of Ws. The proline content of gpa1-4was lower than that of Col, while the ABA content showed no marked difference between these two geneotypes. These data suggested that ATHK1might mediate both proline and ABA accumulation under PEG treatment, while GPA1played roles in proline accumulation but not in ABA accumulation under the same treatment.2. Studies using fluridone, an inhibitor of ABA biosynthesis, as well as exogenous ABA treatment showed that fluridone can partly reduce the proline content of wildtype seedlings after PEG treatment and this effect can be released by supplying exogenous ABA, which implied that proline accumulate after PEG treatment is partly dependent on ABA biosynhtesis. In athkl seedlings, the proline content after12h PEG treatment was lower than that in Ws, but it can be compensated when additionally treated with exogenous ABA, indicating that ATHK1can mediate PEG-induced proline accumulation in an ABA dependent manner. On the contrary, the proline content in gpal-4seedlings after PEG treatment can not be compensated by exogenous ABA addition, suggesting that GPA1mediated PEG-induced proline accumulation in an ABA independent manner.3. Studies using IMD, an inhibitor of NADPH oxidase, as well as exogenous H2O2treatment showed that IMD can partly reduce the proline content of wildtype seedlings after PEG treatment and this effect can be released by supplying exogenous H2O2, which indicated that proline accumulate after PEG treatment is also partly dependent on H2O2biosynthesis. In athkl seedlings, the proline content after12h PEG treatment are lower than that in Ws and this deficit can be compensated when additionally treated with exogenous H2O2, indicating that ATHK1can mediate PEG induced proline accumulation in an H2O2dependent manner. On the contrary, the proline content in gpal-4seedlings after PEG treatment can not be compensated by exogenous H2O2addition, suggesting that GPAI mediated PEG induced proline accumulation in an H2O2independent manner.4. Under a dark condition, the proline content of Arabidopsis seedlings were very low. Light treatment can significantly result in an increase of proline, which indicated that proline biosynthesis might require light. In other word, proline biosynthesis can be induced by light. Under50μM·m-2·s-1light condition, the proline content of athkl and gpal-4are higher than those of their wildtype, respectively, while under300μM·m-2·s-1light intensity, no differences were observed between genotypes, indicating that both ATHK1and GPA1negatively regulate the proline accumulate under50μM·m-2·-1light condition, but under a higher light intensity, their effects disappeared by an unknown mechanism. The proline content of Ws and athkl seedlings show no difference between50μM·m-2·s-1white light and50μM·m-2·s-1blue light conditions. But in the case of Col ecotype, the proline contents under50μM·m-2·s-1blue light is higher than that under50μM·m-2·s-1white light condition, which suggests that50μM·m-2·s-1blue light can induce proline accumulation in the seedlings of Col. In contrary to the case of Col, the proline content of gpal-4showed no difference between such two conditions above, indicateing that GPA1mediates the proline accumulation process induced by50μM·m-2·s-1blue light in Col ecotype.5. The proline content after PEG treatment increased constantly in keeping with the light indensity, indicating that light can promote the PEG induced proline accumulation process. The proline content of athkl after PEG treatment showed no difference from that of Ws under50μM·m-2·s-1light condition. But under300μM·m-2·s-1light condition, the proline content of athkl after PEG treatment was lower than Ws. These data indicated that ATHK1mediated the PEG induced proline accumulate process under higher light intensity (300μM·m-2·s-1) but not under lower light intensity (50μM·m-2·s-1). The proline content of gpal-4is lower than that of Col under not only50μM·m-2·s-1light but also300μM·m-2·s-1light condition, indicating that GPAI mediates the PEG induced proline accumulate process under50or300μM·m-2·s-1light condition. The proline content of both Ws and Col after PEG treatment under50μM·m-2·s-1blue light are lower than that under50μM·m-2·s-1white light, indicating that blue light can inhibit PEG induced proline accumulate process. The proline content of athk1after PEG treatment under50μM·m-2·s-1blue light is lower than that under50μM·m-2·s-1white light,which is similar to Ws. But the proline content of gpal-4after PEG treatment show no differences between blue light and white light, which indicates that GPAI mediates the PEG induced proline accumulation process.In conclusion, proline and ABA content are induced by abiotic stresses. Proline accumulation is partly dependent on ABA and H2O2. Light intensity and light quality also affect the proline accumulation process. In addition, ATHK1and GPAl have partly regulated such processes above.