Photosynthesis and organization of maize mesophyll and bundle sheath thylakoids of plants grown in various light intensities

The aim of this study was to investigate the acclimation of photosynthetic apparatus of maize to different light intensities during growth. Plants were grown at irradiance of 80 (LL), 200 (ML) and 600 (HL) mu mol photons m(-2) s(-1). Our main interest was to understand how the light intensity influences the organization/function of thylakoid complexes in mesophyll (M) and bundle sheath (BS) chloroplasts. We have investigated several physiological parameters including rate of photosynthesis and respiration, the activity of photosystems, fluorescence in RT and at 77 K, phosphorylation of PSII proteins, level of proteins, and organization of thylakoid complexes. We suggest that BS chloroplasts are the main light target. Adjustment of the light absorption and distribution between both photosystems in BS is related to the organization of supercomplexes according to the phosphorylation level. The high rate of phosphorylation of LHCII in BS thylakoids is probably related to the absence of Lhcb3 protein and its replacement by Lhcb1 or Lhcb2 that undergo phosphorylation. In BS thylakoids, for all light conditions the LHCII proteins are bound to PSI, and a high pool of phosphorylated free trimers is present. We conclude that the investigated M and BS chloroplasts use different mechanisms of adjustment and optimization of their function, depending on the optimal or adverse irradiance conditions prevailing during the growth, and that these mechanisms are associated with different light penetration across the leaf. These changes induced by light in both types of chloroplasts are important in the regulation of chloroplast membrane flexibility and thus its function.