Leaf Cuticle and Plasma Membrane Are Critical for a Better Increase of Cotton Salinity Stress Tolerance by l - than d -Gold Nanoclusters

Use of nanoparticles is an emerging approach to improve crop salt tolerance. However, the role of the chirality of nanoparticles in improving crop salt tolerance is still unknown. In this study, chiral gold nanoclusters ( l -AuNCs, 1.62 nm, −20 mV; d -AuNCs, 1.60 nm, −19 mV) with strong/stable fluorescence and similar ROS (reactive oxygen species) scavenging ability were synthesized. Our results showed that foliar-applied chiral AuNCs significantly improved cotton salt tolerance, showing an increase in dry weight (0.38 g for l -AuNCs and 0.28 g for d -AuNCs vs 0.21 g for control), chlorophyll content index (25.3 for l -AuNCs and 22.1 for d -AuNCs vs 20.6 for control), and carbon assimilation rate (5.45 μmol m –2 s –1 for l -AuNCs and 3.06 μmol m –2 s –1 for d -AuNCs vs 2.03 μmol m –2 s –1 for control). The reason behind the superior ability of l -AuNCs over d -AuNCs in improving cotton salt tolerance was attributed to its differential delivery efficiency into cotton leaf cells (73% higher fluorescence intensity of l -AuNCs than d -AuNCs). Further studies confirmed that d -AuNCs have stronger interactions with leaf cuticles, especially octacosane, and lipid membranes, i.e., PIs (phosphatidylinositols) and PGs (phosphatidylglycerols), than l -AuNCs. Confocal imaging analysis, histochemical staining, and ROS content measurements further validated that l -AuNCs-treated cotton seedlings showed significantly less ROS in cotton leaf cells than the d -AuNCs group under salinity. Overall, our results confirmed that the chirality of nanomaterials can affect their capacity to improve salt tolerance due to differential interactions between chiral nanoparticles and leaf cuticles or lipid membranes, showing that chirality is an important property in designing agricultural nanoparticles.