ROS And Auxin Involved In Plant Development In Arabidopsis

Both ROS and auxin are documented to be important in the regulation of plant development and response to environment stress. They also act as important signaling molecules involved in many physiological processes, but the mechanisms underlying the crosstalk between ROS and auxin are poorly understood.This research focuses on these two important signaling molecules. We investigated the mechanisms underlying how ROS and auxin function in plants response to metal stress and regulation of leaf development. Our main results are summarized as follows:1. In this study, microscopic analyses revealed that higher concentration of CuSO4inhibited primary root elongation of Arabidopsis seedlings by affecting both elongation and meristem zones. In meristem zone, meristematic-cell-division potential was reduced by excess Cu. When ethylene-insensitive mutant ein2-1was employed to test whether ethylene signaling pathway was involved in the copper-induced inhibition of root,the data that CUSO4had the similar impact on inhibition of root elongation in both ein2-1and wild-type plants suggested that the inhibition of primary root elongation by Cu was not due to ethylene signaling pathway.Auxin responses were assayed with an auxin responsive DR5::GUS marker line to analyze whether Cu-induced inhibition of primary root elongation is mediated by auxin redistribution or not. Our data shown that excess Cu changed DR5::GUS expression pattern by increasing its activity in both root meristem and elongation zones and decreasing its expression in columella cells, indicating Cu regulation of auxin distribution in the roots.The Cu-treated aux1-7DR5::GUS and pin2DR5::GUS mutant had the increased auxin activities in both root meristem and elongation zones, as Cu-treated DR5::GUS plants did. In addition, AUX1-YFP and PIN2-GFP expression patterns were were not affected by Cu treatment. These results combined with genetic data that both Cu-treated pin2, auxl and wild-type plants exhibited similar inhibition of primary root elongations indicated that neither PIN2nor AUX1participated in Cu-mediated auxin redistribution for its inhibitory role of primary root elongation.Higher auxin activities assayed in both meristem and elongation zones in Cu-treated DR5rev::GFP plants were not detected in pin1DR5rev::GFP exposed to varying concentrations of CuSO4, indicating PINl’s involvement in Cu-regulated auxin distribution. Our experiments show that PIN1-GFP accumulation was dramatically decreased in the roots exposed to excess copper. Furthermore, pin1-1seedlings were exposed to excess copper and the primary root length were statistically analyzed as above. We found that root elongation in pin1-1was relatively insensitive to Cu compared with that of wild-type plants. We also demonstrated that increased H2O2in Cu-treated seedlings did not contribute to Cu-regulated auxin redistribution. Taken together, our data revealed that copper inhibited primary root elongation by changes in auxin distribution via its modulation of PIN1’s expression at least partly, but not AUX1or PIN2.2. H2O2is a very important signal molecule in plant cells. However, it is not clear that whether it involves in the regulation of auxin during plant developmental processes or not. Our study found that the cat2knockout mutant showed hyponastic leaf phenotype with higher concentration of H2O2. We aim at surveying to the relationship between H2O2and auxin in this study. Compared to DR5::GUS line with wild-type background, cat2-1/DR5::GUS lines showed remarkably reduced GUS expression in leaves. If cat2-1mutant was incubated under low light condition, the leaf phenotype change can be rescued in the cat2-1. These results showed that H2O2 may negatively regulated auxin content, thereby affecting the growth of leaves. Futhermore, elevated auxin level in cat2-1mutant can rescue hyponastic leaf phenotype. Taken together, our results demonstrated that hyponastic leaves of the Arabidopsis cat2mutant reveals cross-talk between H2O2and auxin, in which higher H2O2concentration in cat2leaves modulates auxin level via down-regulation of auxin synthesis and results in up-curled leaves.