The Influence Of Light Signal And GAs On Anthocyanins Accumulation Induced By Low Nitrogen In Arabidopsis

Nitrogen is one of macroelement nutrients in plant, which plays an important role in plant growth and development. Low nitrogen stress can influence the synthesis of anthocyanins of plant secondary metabolites. Light signal and hormones are closely related to each other. Studies on the role of light signal and hormone signal in plants under low nitrogen stress is helpful for explaining the influence of stress on the secondary metabolites in plant at molecular level. In this study, the mutants of downstream factor in Arabidopsis photoreceptor and GAs signal mutants were used as the experiment materials and the roles of light signal and GAs in anthocyanin accumulation induced by low nitrogen at the physiological level and transcription level were investigated. The results are as follows:1. It has been found that the marked accumulation of anthocyanin in wild type (Col-0) of Arabidopsis under low nitrogen required the light and sugar. First of all, anthocyanin accumulation was dependent on light. No light was no anthocyanin accumulation. In addition, anthocyanin accumulation was also dependent on sugar application. There was almost no anthocyanin accumulation in seedlings when carbon source (sucrose) concentration in low nitrogen medium was too low. And the anthocyanin accumulation increased with sucrose concentrations increase.2. Phytochrome interacting factors (PIFs) are bHLH type transcription factors, which are negative regulators of photomorphogenesis. The amount of anthocyanin accumulation induced by low nitrogen was obviously decreased in PIF40X and PIF50X than that of Col-0. The genes expression of anthocyanin biosynthesis in PIF40X and PIF5OX’was also greatly down-regulated compared to that of Col-0. The results demonstrated that PIF4and PIF5were the negative regulation factors in anthocyanin accumulation under low nitrogen. Further studies found that phy B positively regulated the anthocyanin accumulation in low nitrogen. COP1(Constitutive photomorphogenic1) is the negative regulator of photomorphogenesis. Compare to Col-0, the anthocyanin content in cop1-4under low nitrogen greatly increased and it greatly decreased in COP1OX. The gene expression by Real-time PCR showed that the related genes of anthocyanin biosynthesis including CHS, DFR and LDOX induced by low nitrogen were up-regulated in cop1-4and down-regulated in COP1OX. These data indicated that COP1was a negative regulator in anthocyanins accumulation under low nitrogen. HY5(Long hypocotyl5) is a bZIP transcription factor which is the earliest deeply researched positive regulator of photomorphogenesis. The experiment with hy5mutant showed that there was almost no anthocyanin accumulation in hy5-215seedlings under low nitrogen, indicating that HY5was necessary for anthocyanin accumulation under low nitrogen. However, the genes expression of anthocyanin biosynthesis in hy5-215seedlings still markedly increased, suggesting that the up-regulation of anthocyanin genes under low nitrogen maybe not totally dependent on HY5pathway.3. The anthocyanin content in Col-0decreased in the application of exogenous GA3. However, the application of Paclobutrazol (PAC, an inhibitor of GA biosynthesis) led to increase in anthocyanin content. The expressions of anthocyanin biosynthesis genes were down-regulated in the present of GA3and up-regulated in the present of PAC. The expressions of anthocyanin synthetic genes in GA20oxl/ox2and GA3oxl/ox2of the double deletion mutants of GA synthesis oxidase were obviously up-regulated, while they were markedly down-regulated in GA2oxl and GA2ox2of GA2oxidase deletion mutants which could make lose GAs activity. In addition, under the condition of low nitrogen, the relative expressions of downstream gene DFR and LDOX in anthocyanin synthesis was obviously up-regulated in gal-3(GA synthesis deletion mutant). The above results show that GAs could negatively regulate anthocyanin accumulation in low nitrogen.4. DELLA protein is the inhibitor of GA signal. The result shows that the amount of anthocyanin in gai-1(Gibberellin acid insensitive-1) under low nitrogen increased, while that of della decreased. In addition, the relative expressions of anthocyanin synthesis genes CHS, DFR, LDOX and UF3GT in della under low nitrogen were down-regulated. However, their relative expressions in gai-1were up-regulated. The above results show that DELLA proteins are the positive regulator in anthocyanins accumulation under low nitrogen.In summary, low nitrogen could induce marked accumulation of anthocyanins in Arabidopsis which depend on light and sugar. PIFs and COP1may negatively regulate anthocyanins accumulation induced by low nitrogen. And the function of HY5in this process is unknown. GAs could negatively regulate the anthocyanins accumulation induced by low nitrogen. The action of DELLA protein is the opposite to that of GAs.