Foliar Delivered Ceo2 Nanoparticles Better Improved Cucumber Salt Tolerance than its Root Application Via Inducing Early Stimulation on Antioxidant System

Salinity is a global issue limiting efficient agricultural production. Cucumber is an important fruit vegetable, but its yield and quality are suffered by salinity stress. Nano-enabled plant salt tolerance is a hot topic. In this study, nanoceria (cerium oxide nanoparticles) with potent ROS (reactive oxygen species) scavenging ability are used to improve cucumber salt tolerance. Our results showed that compared with H 2 O control, no significant difference of H 2 O 2 and O 2 - content, MDA (malondialdehyde) content, relative electric conductivity, and Fv/Fm was found in leaves and/or roots of cucumber before onset of salinity stress, regardless of leaf spray or root application of poly (acrylic) acid coated nanoceria (PNC, 7.8 nm, -31 mV). While, before onset of salinity stress, compared with H 2 O control, the activities of SOD (superoxide dismutase), POD (peroxidase) and CAT (catalase), and the content of GSH (glutathione) and ASA (ascorbic acid) in leaves and roots of cucumber with PNC leaf spray or root application were significantly increased. RNA seq analysis further confirmed that PNC foliar spray upregulates more genes in leaves over roots than the root application. These results showed that foliar sprayed PNC have stronger stimulation effect than the root applied one and leaf are more sensitive to PNC stimulation than root. After salt stress, foliar spray of PNC showed better improvement of cucumber salt tolerance than root application. Plants with foliar sprayed PNC showed significant higher whole plant cerium content than the root application one after salt stress. In summary, we showed that foliar spray of nanoceria is more optimal than root application in terms of improving cucumber salt tolerance, and this improvement is associated with better stimulation on antioxidant system in plants with foliar sprayed PNC than the root applied one