Enhanced Drought Tolerance In Poncirus Trifoliata Via Arbuscular Mycorrhizal Fungus And Nitric Oxide And Mechanism Elucidation

Drought is one of the disadvantages that reduce the crop productivity. Citrus usually has a poor root system with few or no root hair, which results in drought sensitivity in agriculture culture conditions. Arbuscular mycorrhizal fungus is a widespread soil microorganism that could establish a mutually beneficial symbiosis system with most of the terrestrial plants which could help the host plants absorb more water and mineral nutrition and, as a result, enhance the resistance of the host plant to a various of biotic and abiotic stress. Nitric oxide (NO) is a small molecule that is well permeable to plant membrane, and is participanted in protection and signal transduction response to biotic and abiotic stress including drought.In this study, we investigated the probable mechanism of drought tolerance improvement via the arbuscular mycorrhizal fungus inoculation and the application of exogenous nitric oxide, from physiology, biochemical and transcription facets. The general results are lined below.1Inoculation with arbuscular mycorrhizal fungus resulted in growth promotion, accumulation of more chlorophyll, prolines and starch granules in the trifoliate orange seedlings during the normal growth conditions. When exposed to drought stress, the mycorrhizal trifoliate orange seedlings (AM seedlings) contained higher level of chlorophyll, prolines and activities of superoxide dismutase (SOD), peroxide (POD). As a result, drought tolerance was enhanced relative to the non-mycorrhizal trifoliate orange seedlings(NAM seedlings).2The gene chip results showed that the AM seedlings had a higher expression level of some stress-responsive genes such as signaling transduction (NCED3) and functional molecules(MIOX, GLX), which may be responsable for the enhanced drought tolerance.3The seedlings pretreated with the nitric oxide donor SNP (SNP seedlings) contained more nitric oxide during the nornal condition and under dehydration stress. When exposed to dehydration stress, the SNP seedlings contained higher antioxidant activities such as superoxide dismutase (SOD), peroxide (POD) and CAT (catalase), together with a decrease in stomatal aperture, compared to the seedlings pretreated with H2O(H2O seedlings) and the seedlings pretreated with a NO synthetase inhibitor, L-NAME (L-NAME seedlings).When sight in the transcription levels, the SNP seedlings had a higher expression of some stress-responsive genes such as signal transduction (NCED3) and functional molecules (ADC, APX), compared to the H2O scedlings and the L-NAME seedlings, which make the SNP seedlings activate stress defense systems more efficiently and improved the resistance to the dehydration stress.4When exposed to a short drought stress using trifoliate orange potted seedlings, the SNP seedlings accumulated more NO and chlorophyll, showed vigorous photosynthesis and decreased stomatal conductance. As a result, the SNP seedlings alleviated the reactive oxgen species (ROS) damage produed by drought stress, and showed enhanced drought tolerance, compared to the H2O seedlings and the L-NAME seedlings. The SNP seedlings had a higher expression of some stress-responsive genes such as signaling transduction (NCED3) and functional molecules (ADC, APX), compared to the H2O seedlings and the L-NAME seedlings, which make the SNP seedlings activate stress defense systems more efficiently and enhanced the tolerance to the drought stress.