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

田间植物在干旱胁迫下，由于气孔关闭，叶绿体中经常会出现低浓度的CO2。在该条件下对光能的吸收会导致活性氧物种的产生，从而引起光抑制。在低CO2条件下，植物具有多种避免光抑制的机制。在本项目中，我们对叶绿素荧光成像系统进行了改进，以便于分离出在将过量光能安全地耗散为热(热耗散)方面存在缺陷的拟南芥突变体。我们鉴定了npq2和npq4的突变体，这两个突变体在散热机制上存在缺陷。这一结果证实了热耗散对缓解低CO2浓度胁迫的生理意义。根据该缺陷在高光强下诱导热耗散的特性，获得了拟南芥突变体pgr5。在无二氧化碳的空气中，Pgr5也不会引起热耗散。Pgr5在PSI周围的循环电子流活性方面存在缺陷。长期以来，其生理功能一直不清楚，参与该途径的基因PGR5首次被发现。在低CO2浓度条件下，PSI周围依赖于PGR5的循环电子流对于保护光合作用机制是必不可少的。

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.