The avoidance movement of chloroplasts is linked to the lens effect of leaf epidermal cells

Although the phenomenon of chloroplast movement was discovered a long time ago, the physiological role and the structural base for chloroplast movement remain ambiguous, largely due to uncertainties of methodologies. We derived a simple procedure to quantify chloroplast movement as probed by green light, based on leaf transmittance, reflectance, Chl concentration, and the apparent Chl extinction coefficient, and applied it across 10 woody species. The variation in chloroplast movement can be largely explained by differences in the width of cells in the first layer of the palisade mesophyll but not spongy cells. We further found that chloroplast movement in the palisade mesophyll is mainly driven by the lens effect of leaf epidermal cells. Chloroplast movement has little effect on photoprotection in terms of nonphotochemical quenching in 10 studied woody species. The finding of the linkage between chloroplast movement and the lens effect of leaf epidermal cells fills the knowledge gap of chloroplast movement and offers possibilities of working hypotheses regarding the physiological functions of chloroplast movement in future studies.