Compensation Mechanism of the Photosynthetic Apparatus in Mutants.

The origin of chlorophyll deficiency is a mutation () in chlorophyllide oxygenase (CAO), the enzyme responsible for Chl synthesis. Regulation of Chl synthesis is essential for understanding the mechanism of plant acclimation to various conditions. Therefore, the main aim of this study was to find the strategy in plants for compensation of low chlorophyll content by characterizing and comparing the performance and spectral properties of the photosynthetic apparatus related to the lipid and protein composition in four selected Arabidopsis mutants and two Arabidopsis ecotypes. Mutation in different loci of the CAO gene, ., NW41, , and , manifested itself in a distinct phenotype, pigment and photosynthetic protein composition. Changes in the CAO mRNA levels and chlorophyllide (Chlide ) content in ecotypes and mutants indicated their significant role in the adjustment mechanism of the photosynthetic apparatus to low-light conditions. Exposure of mutants with a lower chlorophyll content to short-term (1LL) and long-term low-light stress (10LL) enabled showing a shift in the structure of the PSI and PSII complexes via spectral analysis and the thylakoid composition studies. We demonstrated that both ecotypes, Col-1 and Ler-0, reacted to high-light (HL) conditions in a way remarkably resembling the response of mutants to normal (NL) conditions. We also presented possible ways of regulating the conversion of chlorophyll to depending on the type of light stress conditions.