Investigation of the Global Changes in Photosynthetic Electron Transport in Plants Grown Under Different Light Levels.

To reveal the global regulation of photosynthetic electron transport (PET) in shade plants, the changes in chlorophyll fluorescence induction kinetics (CFI) curves and proteomics were investigated using varieties. There was a significant difference in CFI curves between 'Fire Island' and other varieties (such as 'Sum and Substance') grown under weak light. Weak light induced the appearance of the W phase of CFI curves in the two varieties, which was consistent with a clear decrease in the oxygen-evolving complex and a large upregulation of photosystem (PS) II proteins. In 'Fire Island', the O-J rise of the CFI curves increased faster under weak light than under appropriate light, and this was not only accompanied by a large upregulation of the PS II protein but also a great downregulation in cytochrome b/f, plastocyanin, and PS I. Moreover, weak light resulted in a considerable increase in photosynthetic rate and Rubisco abundance in 'Fire Island', yet the non-photochemical quenching and abundance of CP24 declined significantly. By contrast, weak light had fewer effects on these parameters in 'Sum and Substance'. Therefore, we suggest that the PET is mainly affected by the abundance of PS II, oxygen-evolving complex, cytochrome b/f, plastocyanin, and PS I in plants grown under weak light; meanwhile, the improved photosynthetic capacity under weak light was mainly related to the enhancement of light energy absorption and capture of PS II as well as the increase in the abundance of Rubisco.