Studies On The Mechanisms Of Enhancing The Resistance Of Annual Ryegrass (Lolioum Multiforum) By Exogenous Nitric Oxide Under Temperature Stress

Annual ryegrass(Lolioum multiflorum)were used in this study. After being treated with different contents(0.2,0.5 and 1.0 mmol/L)of exogenous nitric oxide, wheat and ryegrass seedling were stressed at 0℃or 35℃. We probed into the mechanism of nitric oxide on plants under temperature stress by the measures of physiology and biochemistry. The determination showed: 1)the SNP treatment was able to alleviate the accumulation of membrane permeability and MDA content in ryegrass under 35-℃heat and 0℃-chilling stress. After a 3-day recovery, the membrane permeability, MDA content of the seedlings 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 chilling damage. These indicated that the SNP had a function of protecting seedlings from being harmed by chilling stress, and it could alleviate membrane lipid peroxidation induced by stress in ryegrass. 2)Stress is one of the inducements which cause the breaking out of reactive oxygen species (ROS)in plant. SOD,POD and CAT known as defensive mechanism is against high content level of ROS by catalyzing the conversion of O₂^-and toxic H2O2 to oxygen. This research showed that exogenous NO induced the expressions of SOD, POD and CAT. However, the effects on three kinds of antioxidates were different, which might due to different positions of NO situated in signal pathways, or determined by the source-positions or regulation mechanisms of SOD, POD and CAT in membrane lipid peroxidation. 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 chilling stress which would be the confirmation that the damage caused by chilling stress could be avoided to a certain extent by exogenous NO, in particular, the effect of 0.2, 0.5 mmol/L SNP was significant(P<0.05). 3)Proline and soluble sugar are kinds of osmosis in cell, which maintains the completeness of the cell membrane structure. It enables the cell to stabilize protoplasm colloid and the process of metabolism. This experiment showed that exogenous NO could alleviate the damage caused by chilling stress through accumulating praline and soluble sugar. 4) This experiment showed: the contents chlorophyll a,b and Pn could be cut down by temperature stress in ryegrass seedling leaves; the decrease of chlorophyll a,b contents shows that the light-system is impaired and photosynthesis is inhibited. However, NO could maintained a higher level of chlorophyll a,b and Pn in the seedlings treated with SNP due to the treated ones. After a 3-day recovery, the chlorophyll content and Pn of the seedlings treated with SNP got back to the levels of normal seedlings earlier than those of stress control. This revealed that NO could modulate photosynthesis in plant, and increase plant adversity resistance by enhancing photosynthesis. 5)However, due to heat stress, the modulating function of exogenous NO on chilling stress was better in ryegrass.