Regulation Of Photosynthetic Electron Flux Allocation And Osmotic Resistence Of Rumex K-1 By Nitric Oxide

Light energy absorbed by plants is mainly used for photosynthetic carbon assimilation, photorespiration, nitrogen metabolism and Mehler reaction. The light energy allocation determines photoprotection capacity in stress conditions. In order to explore the regulation mechanisms of nitric oxide in photosynthetic electron flux allocation , Rumex K-1, a hybrid of Rumex. patientia×Rumex.tianschaious, and some chemicals involved in metablism of nitric oxide such as nitric oxide scavenger (cPTIO), nitric oxide donor(GSNO) and nitric oxide synthetase inhibitor (L-NAME) were used combined with different osmotic treatments (0 and 20%PEG) in this study.1. In normal water conditions, nitric oxide scavenger (cPTIO) decreased net photosynthetic rate (Pn), actual PSâ…¡photochemical efficiency(ФPSII), stomatal conductance (Gs), photosynthetic electron flux used for photosynthetic carbon assimilation (Je(PCR)), photosynthetic electron flux used for photorespiration (Je(PCO)), photosynthetic electron flux used for nitrogen metabolism (Ja(O₂-independ)) , carboxylation efficiency(CE), nitrate reductase (NR) activity, glutamine synthetase (GS) activity and glycolate oxidase (GO) activity, however, it increased photosynthetic electron flux used for Mehler reaction (Ja(O₂-depend)) and intercellular CO₂ concentration (Ci). Nitric oxide donor (GSNO) reversed these effects of nitric oxide scavenger (cPTIO) on Rumex K-1 leaves, which indicates that nitric oxide was involved in the regulation of photosynthetic electron flux allocation.Nitric oxide scavenger (cPTIO) decreased carbon and nitrogen metabolism and induced photoinhibition .While application of external nitric oxide increased carbon and nitrogen metabolism and decreased photoinhibition.2. Nitric oxide synthetase inhibitor (L-NAME) decreased photosynthetic electron flux used for carbon and nitrogen metabolism and key enzymes activities in carbon and nitrogen metabolism.The inhibition effects of L-NAME was similar to those of cPTIO , which indicates that nitric oxide synthetase was the main source of nitric oxide in Rumex K-1 and L-NAME regulated light energy allocation through nitric oxide.3. Under osmotic stress (20%PEG) shock , net photosynthetic rate(Pn), actual PSâ…¡photochemical efficiency(ФPSII), stomatal conductance(Gs), photosynthetic electron flux used for photosynthetic carbon assimilation (Je(PCR)), photosynthetic electron flux used for photorespiration (Je(PCO)), photosynthetic electron flux used for nitrogen metabolism (Ja(O₂-independ)) , carboxylation efficiency(CE), Rubisco activase content, nitrate reductase (NR) activity, glutamine synthetase (GS) activity, glycolate oxidase (GO) activity decreased while Mehler reaction (Ja(O₂-depend)) and intercellular CO₂ concentration (Ci) increases. Addition of nitric oxide restored the above effects, which indicates that nitric oxide was involved in photosynthetic excitation energy allocation under osmotic stress shock.4. Photosynthetic excitation energy allocation under different nitrogen application was different in osmotic stress. Carbon and nitrogen metabolism in leaves treated with 0 mmol L^-1NO₃^- and 30 mmol L^-1NO₃^- under osmotic stress decreased significantly but it decreased slightly in leaves treated with 15 mmol L^-1NO₃^- .Addition of nitric oxide reversd these osmotic effects , which indicates that nitric oxide was involved in regulation of osmotic resistence under different nitrogen application under osmotic stress.5. Nitric oxide regulated photosynthetic electron flux allocation between carbon and nitrogen metabolism and Mehler reaction . Although Mehler reaction dissipates some excessive excitation energy , it produces lots of ROS which is dangerous to plant. So Mehler reaction is not the first choice of photoprotection in Rumex K-1 plant.6. Our study demostrated that, under osmotic stress, nitric oxide regulated the activity of Rubisco by altering the content of Rubisco activase in leaves of Rumex K-1 to accomplish regulation of photosynthetic electron flux allocated to CO₂ assimilation.