Effects Of Exogenous Nitric Oxide On Drought-Resistance Of Walnuts (Juglans Regia L.)

One-year old wulnuts (Juglans regia L.)were treated with different contents (250,500和1000μmol/L) of exogenous nitric oxide under drought stress. Then we studied how nitric oxide enhanced the resistance ability of plants under drought stress through physiological and biochemical methods.The main results were as follows:1. The SNP treatment was able to alleviate the accumulation of membrane permeability and MDA content in walnuts under drought stress. After a 3-day recovery, the membrane permeability and MDA content of the wulnuts treated with SNP got back to the levels of normal seedlings, while those of stress seedlings were not able to get recovery completely due to the drought damage. In particular, the effects of 500μmol/l SNP was most significant, 250μmol/LSNP and 1000μmol/L SNP followed.2. Stress was one of the inducements which cause the breaking out of reactive oxygen species (ROS)in plant. SOD,POD and CAT were known as defensive mechanism against high content level of ROS by catalyzing the conversion of O2·–and toxic H2O2 to oxygen. SOD activity and CAT activity rised first; then followed by a drop. After SNP treatment, both SOD activity and CAT activity were increased under drought stress. After 3 days resumed growth, the membrane permeability and the activities of antioxide enzymes of the treated ones recovered earlier than those of control ones under drought stress, which would be the confirmation that the damage caused by drought stress could be avoided to a certain extent by exogenous NO, In particular, the effect of 500μmol/l SNP was most significant, 250μmol/LSNP and 1000μmmol/L SNP followed.3. Proline and soluble sugar are osmotic regulators in cell, which maintained the completeness of the cell membrane structure. It enabled the cell to stabilize protoplasm colloid and the process of metabolism. This experiment showed that exogenous NO could alleviate the damage caused by drought stress through accumulating proline and soluble sugar. After 3 days resumed growth, proline and soluble sugar content of the seedlings treated with SNP got back to the levels of normal seedlings, while those of drought stress seedlings were not able to get recovery completely due to the drought damage. 4. Drought stress significantly decreased chlorophyll content, photosynthetic rate (Pn), transpiration rate (Tr), stomatal conductance (Gs) and chlorophyll fluorescence photochemical efficiency of PSII (Fv/Fm), quantum yield of PSII (ΦPSII) , photochemical quenching coefficient (qP) and non-photochemical quenching of fluorescence (NPQ) in leaves of wulnuts. NO treatment increased chlorophyll content, Pn, Tr, Gs and Fv/Fm,ΦPSII, qP and NPQ under drought stress. Intercellular CO2 concentration (Ci) dropped first,followed by a rise under drought stress.The Ci of leaves treated with NO continued to decrease, but with a small extent. This revealed that NO could modulate photosynthesis in plant, and increase plant adversity resistance by enhancing photosynthesis.