Tanaka Ryouichi, Tanaka Ayumi
Institute of Low Temperature Science, CREST, Hokkaido University, Japan Science and Technology Corporation, N19 W8, 060-0819 Sapporo, Kita-ku, Japan.
Photosynth Res. 2005 Sep;85(3):327-40. doi: 10.1007/s11120-005-6807-z.
Land plants change the compositions of light-harvesting complexes (LHC) and chlorophyll (Chl) a/b ratios in response to the variable light environments which they encounter. In this study, we attempted to determine the mechanism which regulates Chl a/b ratios and whether the changes in Chl a/b ratios are essential in regulation of LHC accumulation during light acclimation. We hypothesized that changes in the mRNA levels for chlorophyll a oxygenase (CAO) involved in Chl b biosynthesis are an essential part of light response of Chl a/b ratios and LHC accumulation. We also examined the light-intensity dependent response of CAO-overexpression and wild-type Arabidopsis thaliana plants. When wild-type plants were acclimated from low-light (LL) to high-light (HL) conditions, CAO mRNA levels decreased and the Chl a/b ratio increased. In transgenic plants overexpressing CAO, the Chl a/b ratio remained low under HL conditions; thereby suggesting that changes in the CAO mRNA levels are necessary for those in Chl a/b ratios upon light acclimation. Under HL conditions, the accumulation of Lhcb1, Lhcb3 and Lhcb6 was enhanced in plants overexpressing CAO. On the contrary, in a CAO-deficient mutant, chlorina 1-1, theaccumulation of Lhcb1, Lhcb2, Lhcb3, Lhcb6 and Lhca4 was reduced. In comparison to wild-type, beta-carotene levels were reduced in CAO-overexpressing plants, while they were elevated in chlorina 1-1 mutants. These results imply that the transcriptional control of CAO is a part of the regulatory mechanism for the accumulation of a distinct set of LHC proteins upon light acclimation.
陆生植物会根据所遇到的多变光照环境改变捕光复合物（LHC）的组成和叶绿素（Chl）a/b 比值。在本研究中，我们试图确定调节 Chl a/b 比值的机制，以及 Chl a/b 比值的变化在光适应过程中对 LHC 积累的调节是否至关重要。我们假设参与 Chl b 生物合成的叶绿素 a 加氧酶（CAO）的 mRNA 水平变化是 Chl a/b 比值和 LHC 积累光响应的重要组成部分。我们还研究了 CAO 过表达和野生型拟南芥植株对光强的依赖性反应。当野生型植株从低光（LL）适应到高光（HL）条件时，CAO mRNA 水平下降，Chl a/b 比值增加。在过表达 CAO 的转基因植株中，HL 条件下 Chl a/b 比值仍保持较低水平；因此表明，光适应时 CAO mRNA 水平的变化对于 Chl a/b 比值的变化是必要的。在 HL 条件下，过表达 CAO 的植株中 Lhcb1、Lhcb3 和 Lhcb6 的积累增强。相反，在 CAO 缺陷型突变体 chlorina 1-1 中，Lhcb1、Lhcb2、Lhcb3、Lhcb6 和 Lhca4 的积累减少。与野生型相比，过表达 CAO 的植株中β-胡萝卜素水平降低，而在 chlorina 1-1 突变体中则升高。这些结果表明，CAO 的转录调控是光适应时一组不同的 LHC 蛋白积累调控机制的一部分。
