Molecular Genetic Analysis of the Regulation of Photosynthesis under low CO2 Conditions

在干旱胁迫下，植物往往通过关闭气孔来应对叶绿体中低浓度的CO2。在这种条件下光能的吸收导致活性氧的产生，引起光抑制。在低CO2条件下，植物有多种机制来避免光抑制。在本项目中，我们对叶绿素荧光成像系统进行了改进，以便于分离出过量光能安全作为热量（热耗散）耗散缺陷的拟南芥突变体。我们发现了npq2和npq4等位突变体，它们在散热机制中存在缺陷。结果证实了热耗散对缓解低CO2浓度胁迫的生理意义。利用高光强诱导热耗散的缺陷，分离出拟南芥突变体pgr5。Pgr5也不能在无二氧化碳的空气中诱导热耗散。Pgr5在PSI周围的循环电子流活动中存在缺陷。长期以来，其生理功能一直不清楚，PGR5基因参与了这一途径。在低CO2浓度条件下，PSI周围依赖pgr5的循环电子流对保护光合机制至关重要。

The plants in the field often encounter low concentration of CO2 in the Chloroplast by the stomata closure responding to the drought stress. Absorbance of light energy under the conditions leads to the generation of active oxygen species, causing photoinhibition. Plants have multiple mechanisms to avoid photoinhibition under the low CO2 conditions. In this project we have modified the chlorophyll fluorescence imaging system to facilitate the isolation of Arabidopsis mutant defective in the dissipation of excessive light energy safely as heat (thermal dissipation). We identified mutants allelic to npq2 and npq4 which are defective in the machinery of thermal dissipation. The results confirmed the physiological significance of thermal dissipation to alleviate the stress of low CO2 concentration.Arabidopsis mutant pgr5 was isolated depending on the defect to induce thermal dissipation at high light intensity. Pgr5 also cannot induce thermal dissipation in the CO2-free air. Pgr5 is defective in the activity of cyclic electron flow around PSI. The physiological function has been unclear for long and the gene PGR5 participates in the pathway was first identified. The PGR5-dependent cyclic electron flow around PSI is essential to protect photosynthetic machineries under low CO2 concentration conditions.