Nanoceria improves leaf hydraulic conductance and mesophyll conductance to CO2 in drought-stressed cotton by modifying leaf anatomy

Drought negatively impacts photosynthesis and water transport in plants, so new technologies to enhance drought tolerance are urgently needed. Here, a hydroponic experiment revealed that foliar application of polyacrylic acid-coated nanoceria (PNC, 100 mg L −1 ) to cotton leaves under drought stress (DS, 5% (w/v) polyethylene glycol 6000, 5 d) significantly improved the growth performance and biomass accumulation. Compared with the DS control, foliar application of PNC under DS conditions (DP) significantly improved leaf hydraulic conductance ( K leaf ) and mesophyll conductance ( g m ) by 73.4% and 34.9%, respectively, thereby leading to 42.2% higher net photosynthetic rate ( A ). Moreover, compared with the DS control, the DP treatment considerably increased the volume fraction of intercellular airspace and the surface area of mesophyll cells exposed to intercellular airspace by 24.5% and 56.3%, respectively, which contributed to the simultaneous improvements in g m and outside-xylem hydraulic conductance ( K ox ). Furthermore, relative to the DS control, the DP treatment considerably decreased hydrogen peroxide and superoxide anion levels by 45.2% and 65.4%, respectively, which largely explained the variations in above mentioned leaf anatomy. Additionally, compared with the DS control, enhancement in K ox under the DP treatment was also ascribed to the increased leaf vein density. Therefore, these findings indicated that foliar application of nanoceria could improve both K leaf and g m by modifying leaf anatomy, thereby improving the A of drought-stressed cotton seedlings.