Nanoceria-induced variations in leaf anatomy and cell wall composition drive the increase in mesophyll conductance of salt-stressed cotton leaves.

Nanomaterials as an emerging tool are being used to improve plant's net photosynthetic rate (A) when suffering salt stress, but the underlying mechanisms remain unclear. To clarify this, a hydroponic experiment was conducted to study the effects of polyacrylic acid coated nanoceria (PNC) on the A of salt-stressed cotton and related intrinsic mechanisms. Results showed that the PNC-induced A enhancement of salt-stressed leaves was strongly facilitated by the mesophyll conductance to CO (g). Further analysis showed that the PNC-induced improvement of g was related to the increased chloroplast surface area exposed to intercellular airspaces, which was attribute to the increased mesophyll surface area exposed to intercellular airspaces and chloroplast number due to the increased K content and decreased reactive oxygen species level in salt-stressed leaves. Interestingly, our results also showed that PNC-induced variations in cell wall composition of salt-stressed cotton leaves strongly influenced g, especially, hemicellulose and pectin. Moreover, the proportion of pectin in cell wall composition played a more important role in determining g. Our study demonstrated for the first time that nanoceria, through alterations to anatomical traits and cell wall composition, drove g enhancement, which ultimately increased A of salt-stressed leaves.