Effects Of Nitric Oxide On Photosynthetic PS ⅡEnergy Distribution And Its Regulative Resistance To Drought In Mulberry

Heilongjiang Province is the main production base of commodity grain in China, however, environmental changes affect crop production, especially the early spring drought in the northwest region of Heilongjiang province limits the production of the grain. The most main factors of drought reducing the plants production is the reduction of photosynthetic production. The drought affects the enzyme system of photosynthesis directly, and limits carbon assimilation of dark reaction process, which makes light system Ⅱ capturing light energy and electron transfer process limited. If not cleaning up the excess light energy in time, it will lead to photoinhibition, and in turn affect the photosynthesis, reduce the plant biological production. Nitrc oxide (NO) is a important kind of signal molecules in plants, and involved in many plant physiological process adjustment, especially protecting PS Ⅱ is of great significance. Along with the implementation of our country’s the policy of "South Mulberries Move to the North", mulberry (Morus alba L.) has a large area of cultivation in Heilongjiang Province. In order to make the mulberry gain the higher yield of blade, we discusse the regulatory mechanism of NO for the photosynthesis of mulberry under the drought condition, for the purpose of improving the drought resistance of the mulberry trees. Therefore, this test treating "Qing Long Mulberry" which has a large cultivation area in Heilongjiang Province, as the experimental material, with the method of20%polyethylene glycol-6000(PEG-6000) simulating the drought, controlling NO in the mulberry body (NO donor sodium nitrate tome, SNP; NO scavenger, cPTIO; NO synthase inhibitors, L-NAME), researchs the fuction of NO for the photosynthetic energy allocation and reulation of mulberry trees under the drought, on the one hand, filling the content of the light energy distribution in mulberry photosynthetic physiological theory, on the other hand, to provide technical support for the production of mulberry trees. The results are as follows:1. PEG simulating drought reduced the mulberry leaf stomatal conductance (Cs) and net photosynthetic rate (Pn), but increased leaf intercellular CO2concentration (Ci). The decrease of the mulberry seeding photosynthetic ability caused by PEG simulating drought is the result of the joint action of stomatal and non-stomatal factors. The mulberry root applying lmmol·L-1SNP can alleviate the photosynthetic reduction phenomenon of the mulberry seeding leaves caused by the drought, which compared with PEG treatment, mulberry leaf photosynthetic capacity increased significantly, light full ensuring maximum photosynthetic rate (Amax) and light saturated point (LSP) were increased significantly, and the light compensation point (LCP) is decreased obviously. As the same time, the SNP can alleviate the decrease of Tr and WUE caused by the drought. SNP is an effective NO donor, and the increase of NO regulates the mulberry stomatal movement, especially under dry conditions increases the stomatal opening, and increases the photosynthetic capacity of mulberry trees, so this is the main factor of NO easing the stomatal imitation factors under the drought. On the other hand, PEG treatment reduces the maximum photochemical efficiency and electron transfer rate of mulberry leaves, however roots applying lmmol-L-1SNP under the drought condition improved the proportion of PS Ⅱ absorbing light energy used in the photochemical reaction (ΦPSⅡ), reduced the proportion of heat dissipation (ΦNPQ), indicating that NO changed the distribution of PS II reaction center absorbing light energy, relieved the decrease of the ΦPSⅡ effectively, maintained the photosynthetic electron transfer and the activity of PS II reaction center of mulberry under drought stress. It is the main factors of NO easing the non-stomatal limitation of the mulberry under the drought. SNP increased the activity of antioxidant enzymes(SOD and POD) under the drought condition, at the same time promoted the activity the nitrate reductase(NR), enhanced the ability of nitrogen metabolism of the mulberry, shunted the excess light energy caused by the drought, and improved the drought resistance of the mulberry trees.2. The mulberry root applying0.5mmol·L-1cPTIO reduced Pn of the mulberry leaf and inhibited the photosynthetic capacity, but cPTIO under the PEG simulating drought exacerbated the inhibition of the mulberry photosynthetic capacity. cPTIO processing mulberry roots reduced the mulberry photosynthetic electron transfer, and PS II light energy conversion efficiency drops, excess excitation energy increased, however, under drought stress, the cPTIO further decreased the photochemical activity of mulberry leaves and the electron transfer rate. Combined with the SNP results, we found that:cleaning up NO in the mulberry body can lower the mulberry seeding leaf photosynthetic capacity. aggravate the degree of photoinhibition under drought stress, explaining that NO regulated the process of the plant carbon assimilation, leading to the excess accumulation of light energy of PS Ⅱ system, the reduction of PS Ⅱ reaction center activity, and the decline of mulberry photosynthetic efficiency.3. Roots applying NO synthetase inhibitors (L-NAME) reduced the photosynthetic capacity of mulberry, however application of SNP eliminated the suppression of L-NAME to photosynthetic capacity, indicating that NO synthase plays an important role in regulating mulberry photosynthesis. Under the PEG simulating drought stress. L-NAME exacerbated the decrease of the mulberry photosynthetic capacity. however. SNP not only alleviated the decrease of the photosynthesis under drought, but also could reduce the the mulberry leaf photosynthesis decline phenomenon caused by the L-NAME. From the Pn-PAR curve analysis, we can know that L-NAME caused the carboxylation efficiency decrease, inhibited the activity of the photosynthetic enzyme during the photosynthetic carbon assimilation process, further led to the reduction of the leaf PS II photochemical activity and the electron transfer rate, which makes the light energy conversion efficiency of the mulberry leaves decrease obviously, and outside applying SNP can ease the reduction caused by L-NAME. L-NAME reduced the activity of NR obviously, which can be eliminated by SNP, illustrating that the reason why L-NAME caused lower photosynthetic capacity is the lower ability of nitrogen metabolism in the body.In conclusion, first of all, the first site of the reduction of the plant photosynthetic capacity caused by the drought is a process of photosynthetic carbon assimilation. The decrease of the photosynthetic enzyme activity leads to the excess light energy during the photochemical process, which causes the photoinhibition, reducing the photosynthetic efficiency in feedback type, which breaks through the view of the drought leading to the reduction of photochemical efficiency that causes the photosynthetic capacity decline. Secondly, the decrease of NO in plants leads to the decline in photosynthetic carbon assimilation ability, which exacerbates the photoinhibition, however adding NO in vitro can enhance the activity of SOD and POD, promote the NR activity, enhance the ability of mulberry nitrogen metabolism, shunt the excess light energy caused by the drought, and alleviate the photoinhibition. Therefore, exogenous NO can improve the drought resistance of plants.