The Effects Of NO Signal Transduction On Cell Wall Of Pea (Pisum Sativum L.) Under UV-B Radiation

Depletion of the stratospheric ozone layer cause an increase in solar ultraviolet-B (UV-B, 280-320 nm) radiation reaching the Earth's surface. Enhanced UV-B radiation will have adverse effects on growth, development, and metabolism of plant. Nitric oxide (NO) is a multifunctional bioactive molecule and suggested to as signal involving in responses to biotic and abiotic stresses in plants. Little is known about the functions of NO as signal under UV-B radiation. In this study, the signaling mechanisms of NO and the effects of NO on cell wall polysaccharides under UV-B radiation (ambient plus 4.8 KJ/m^-2 d^-1 of supplemental biological effective UV-B radiation;simulating a 20% ozone depletion of Lanzhou at summer solstice,) were studied. The results as following:1. The stem length and xyloglucan-degrading activity in cell wall of pea seedlings were induced by UV-B radiation. And UV-B radiation increased the NO generation and NOS activity in cytosolic fraction in pea stems and inhibited NOS activity in microsomol fraction in pea stems. SNP had the similar effects on stem length, xyloglucan-degrading activity in cell wall, NO generation and NOS activity with UV-B radiation. LNNA and PTIO had the opposite response to UV-B radiation. PTIO had no effects on the NOS activity. These results indicated that UV-B-induced growth inhibition might achieve through modification of the mechanical properties of cell wall polysaccharides, which was probably mediated by the change of xyloglucan-degrading activities in cell wall. NO might be as a signal regulating the xyloglucan-degrading activities in cell wall.2. The changes in the amount of HA components were not directly correlation with stem growth. The changes of total sugar and uroinc acid in HA were different with cell wall materials, increasing sharply and decreasing rapidly. UV-B radiation increased the amounts of total sugar and uronic acid per unit length in HA. SNP mimicked the effects of UV-B radiation on HA. LNNA and PTIO blocked the effects of UV-B radiation on HA. The synthesis of HA polysaccharides seems to be associated with the cessation of growth. NO induced by UV-B radiation regulated theamounts of HA, and then achieved UV-B-induced growth inhibition.3. The cell wall contents per unit length were decreased with the growth and development day. The changes of total sugar and uronic acid per unit length in pectin, hemicellulose B and cellulose were similar with the changes of cell wall per unit length contents. Analysis of cell wall composition indicated that the amounts of cell wall, HB and cellulose were correlated with the stem growth. The correlation coefficients were above 0.96. UV-B radiation increased amounts of total sugar and uronic acid in cell wall polysaccharides and changed the ratio of total sugar and uronic acid in pectin. SNP treat had the similar effects on the amounts of cell wall, HA, HB and cellulose with UV-B radiation. LNNA and PTIO has the opposite effects on the amounts of cell wall, HA, HB and cellulose with UV-B radiation. These results indicated that the decrease of cell wall polysaccharides per unit length might lead to decrease in the thickness of the cell wall. The results further confirmed that the growth inhibition induced by UV-B was achieved through modification the composition of the cell wall polysaccharides and chemical properties of cell wall, which was induced by nitric oxide mediated-changes of enzymes activities in cell wall.4. Under CK condition, the levels of NO was very low, and endogenous NO induced the activities of NOS and NO production. Under UV-B radiation, the levels of NO was very high, and endogenous decreased the activities of NOS and NO production. The double regulation of NOS activities, by NO led to increase of NO rapidly and diminish of NO soon. These might led to a optimum concentration of NO in vivo. And then NO could mediate the effects of UV-B radiation quickly and at same time, the cell could not be damage by the accumulation by NO.5. Compared with the roles of LNNA and PTIO, we found that there had other originates of NO in UV-B-induced growth inhibition. SNP had not effects the amounts of pectin. LNNA and PTIO could not weaken the increase of the amounts of pectin under UV-B radiation. The result indicated that there might have other signal pathways. NO originated from different sources and different signal pathways might interact with each other and form a signal network. UV-B radiation might regulate thegrowth inhibition through the signal network.Summary, UV-B radiation produced the NO in different sources and other signal molecular. These signals interacted with each other regulating the activity cell wall enzymes or regulating alone, then the composition and chemical properties of wall polysaccharides were changed, rigidifying the cell wall, reducing the growth. These results proved the theories for improving the resistance of plants.