Reductions in mesophyll conductance under drought stress are influenced by increases in cell wall chelator-soluble pectin content and denser microfibril alignment in cotton.

This article investigates how drought stress affects leaf cell wall structure and composition in cotton (Gossypium hirsutum L.) and its impact on mesophyll conductance to CO₂ diffusion (gₘ), a key factor limiting photosynthesis. Under increasing drought, cotton leaves exhibited thicker cell walls (T_cw), increased cellulose content and microfibril diameter with a more parallel alignment, and elevated chelator-soluble pectin, while hemicellulose content decreased. These compositional and ultrastructural changes collectively reduced cell wall porosity and increased resistance to CO₂ diffusion, thereby lowering gₘ. The study highlights that drought-induced reductions in gₘ are not solely due to thicker cell walls but also involve specific modifications in cell wall components and microfibril arrangement, emphasizing the complex regulation of leaf gas exchange under water deficit conditions.