Light-Dependent Reactions of Photosynthesis in Mesophyll and Bundle Sheath Chloroplasts of C4 Plant Maize. How Our Views Have Changed in Recent Years

Plants experience a range of light intensities and qualities in their environment. Leaves are subjected to spatial and temporal gradients in incident light, which has major consequences in the photosynthetic carbon assimilation. Plants acclimate to light by developing a range of mechanisms, from adjustments in leaf morphology to changes in the photosynthetic apparatus stoichiometry. In C4 plants, light intensity is a major limiting factor for photosynthesis at optimum temperatures. Under limiting light, it is not clear if all of factors (e.g., temperature, mineral nutrition, water supply) are co-limiting or if there is one primary limitation. Differences in light quality and intensity have a profound impact on C4 photosynthesis, where pathways require metabolic coordination of the mesophyll and bundle sheath cycles. Changes in the linear versus cyclic electron flux in maize (NADP-malic enzyme C4 subtype) in the mesophyll and bundle sheath chloroplasts in response to light may lead to an imbalance in the coordination of the C3 and C4 pathways. Additionally, the rearrangement of the thylakoid complexes of both types of chloroplasts in maize optimizes the light energy distribution between the mesophyll and bundle sheath cells and may also participate in energy dissipation. This review aims to highlight the changes in the understanding of the functions of photosystem II in maize bundle sheath chloroplasts and the role of super and megacomplexes in the thylakoids.