Signal Transduction Of Anthocyanin Accumulation And CHS Expression In Arabidopsis Thaliana Induced By Blue Light

Numerous experiments have indicated that anthocyanin biosynthesis in higher plants is regulated by light and blue light is one of the most effective factors to stimulate anthocyanin accumulation in seedlings. Although several reports have been published for the components involved in signaling pathway of light-controlled pigmentation, evidence of extracellular Ca2+and CaM involved in blue light induced anthocyanin accumulation and CHS expression is still limited.WT and hy4 of Arabidopsis thaliana (Landsberg) were used in the experiments. The components involved in the signaling pathway of blue-light-induced anthocyanin accumulation and CHS expression were investigated by pharmacological approach. The main results are as follows:1. Blue-light-induced anthocyanin accumulation and CHS expression inArabidopsis13-d-old seedlings of WT and hy4 Arabidopsis grown under white light (WL) with the light fluence rate of 20μmol·m-2·s-1 were transferred into blue light (BL) and irradiated for period of time with different fluence rates before harvesting. The leaves isolated from the seedlings showed an increase in the anthocyanin content. The BL response was fluence dependent and the anthocyanin content increased with the irradiating time under the same fluence rate. Our results supplied another evidence that blue-light-induced anthocyanin accumulation was a high irradiance response (HIR) in plant photomorphogenesis. Anthocyanin content in hy4 mutant was lower than that in WT Arabidopsis after BL treatment and it was demonstrated that cryptochrome 1 (cry1) mediated the BL response in anthocyanin accumulation.Chalcone synthase (CHS) gene expression in the WT leaves was induced by BL and it could be detected at 4 h and reached a peak at 8 h in BL. And then the gene expression declined. Blue light could not induce any gene expression in hy4 mutant indicating cryl is the photoreceptor mediating the blue-light-induced CHS gene expression.2. Components involved in blue-light-induced anthocyanin accumulation andCHS expression in Arabidopsis1) Ca2+/ CaMThe Ca2+ in the medium was essential for the blue-light-induced anthocyanin accumulation. BL response was blocked without Ca2+ and could be enhanced by the application of A23187, a calcium ionophore. The anthocyanin accumulation induced by BL was inhibited by EGTA and two nonpermeable L-type channel blocker verapamil and nifedipine (Nif). CHS gene expression induced by BL was enhanced by A23187 and inhibited by EGTA and verapamil. But the effect of another Ca2+ channel blocker Nif on the gene expression was opposite to its role in the inhibition of anthocyanin accumulation. Our data demonstrated that extracellular Ca2+ was required for blue-light-induced anthocyanin accumulation and CHS gene expression and verapamil sensitive plasma membrane Ca2+ channel played a positive effector on BL response.Heparin, an antagonist of IP3 receptor increased the anthocyanin content induced by BL but inhibited CHS gene expression. LiCl3, an inhibitor of IP3 pathway, showed an inhibition of the pigmentation but had a positive effect on gene expression. Inositol supplied in the medium enhanced both blue-light-induced pigmentation and gene expression.Antagonists of CaM trifluoperazine (Tfp) and W7 were used for detecting the role of CaM in BL response. It was showed that the former had a positive and the later had a negative effect on BL response.There is still a question to be addressed whether intracellular IP3 sensitive calcium store and CaM are involved in BL response mediated by cry 1. There should be a fine regulating process of Ca2+/CaM in the blue-light-induced anthocyanin accumulation and CHS gene expression in Arabidopsis.Application of most pharmacological chemicals such as A23187, EGTA, Nif, verapamil, heparin and inositol did not show significant effect on athocyanin accumulation after BL treatment in hy4 mutant. This indicated that the Ca2+ play an important role in cryl specific signaling.2) Components in plasma membraneE...