The role of chloroplast movement in C₄ photosynthesis: a theoretical analysis using a three-dimensional reaction–diffusion model for maize.

This article focuses on the development and application of a three-dimensional (3D) reaction–diffusion model of C4 photosynthesis in maize leaves to investigate how chloroplast movement within mesophyll cells affects the CO2 concentrating mechanism (CCM) efficiency and photosynthetic performance. The model integrates detailed 3D leaf anatomy, light propagation, ATP and NADPH production, and gas diffusion processes, enabling simulation of different chloroplast arrangements: aggregative movement (chloroplasts moving toward bundle sheath cells) and avoidance movement (chloroplasts aligning to allow light passage). Results indicate that aggregative movement increases light absorption by bundle sheath chloroplasts, ATP and NADPH production, and net photosynthetic rate at high light intensities but also raises CO2 leakiness, reducing CCM efficiency. Conversely, avoidance movement decreases photosynthesis and ATP production while also increasing leakiness. The study highlights the importance of coordinated increases in electron transport and Rubisco activity to optimize CCM efficiency under high light and demonstrates that 3D modeling provides enhanced mechanistic insights into the interplay between leaf anatomy, chloroplast positioning, and photosynthetic function in C4 plants.