Study On The Regulation Of Endogenous Nitric Oxide And Reactive Oxygen Species On Physiological Characteristics In Wheat Seedlings

Nitric oxide(NO)and reactive oxygen species(ROS)play a very important role in the signal transduction of plants,but the signal effect is closely related to the concentration.ROS can be used as a second signal molecule to regulate plant cell responses at low or appropriate concentrations,including seed germination,stomatal closure,root organogenesis,programmed cell death,and defense of biological and abiotic pressures.But the concentration of NO not more is betteris,the excess will also produce toxic effects on plants.In addition,NO can interact with ROS signaling pathway to regulate plant hypersensitivity,cell death,senescence,and proline metabolism.Therefore,the study of NO and ROS is of great significance to understand the changes of physiological and biochemical characteristics in plants.In the study new spring wheat seedlings(Triticum aestivum L.,cv Longchun 27)was treated with PTIO(NO specific scavenger),catalase(CAT,H2O2 scavenger)or DPI(plasma membrane NADPH oxidase inhibitors)to investigate the generation endogenous NO and apoplastic ROS and to explore their effects on seedlings growth,antioxidation response and proline metabolism,elemental content and so on.The main results are as follows:1.The length of roots lowered in CAT-treated seedlings.Differently,PTIO or DPI significantly inhibited growth of roots and shoots.The addition of PTIO,CAT and DPI inhibited the synthesis of chlorophyll a,chlorophyll b and carotenoids,but only CAT and DPI had a significant effect,and the total chlorophyll content was also decreased.2.PTIO or DPI induced the increases of molondialdehyde(MDA)content,with the largest elevation due to DPI treatment.The content of MDA in leaves of seedlings was decreased by CAT treatment,but CAT did not affect MDA content in roots.CAT treatment had no significant effect on the cell viability of root tip in wheat seedlings,but PTIO and DPI treatment significantly increased the evans blue content into cells.3.PTIO treatment resulted in the reduction of NO content in leaves and roots as well as total ROS contents in leaves but the increase of total and apoplastic ROS in roots.After the seedllings were treated with CAT,the amount of NO and total hydrogen peroxide(H2O2)in leaves and apoplastic H2O2 content in roots lowered,while hydroxyl radical(·OH)content in leaves and NO together with total and apoplastic superoxide anion(O2?-)contents in roots significantly increased.In contrast,NO and total H2O2 contents decreased in roots but rose in leaves in DPI-treated seedlings.Meanwhiles,DPI resulted in significant reduction of apoplastic ROS in roots but increases of total O2?-and ·OH in roots and leaves.4.The activities of superoxide dismutase(SOD),Glutathione reductase(GR),CAT in leaves and peroxidase(POD)in roots showed on obvious changes under PTIO treatments,While the activities of SOD in roots and POD in leaves increased,CAT and ascorbic acid peroxidase(APX)activities decreased in roots.CAT-treated did not affect the activities of CAT in leaves and SOD,POD or GR in roots,but SOD in leaves or CAT,APX in roots activities decreased,and POD,APX,GR activities enhanced in leaves.The activities of SOD in roots and leaves or CAT,POD,GR in leaves was improved by the addition of DPI,CAT and POD in roots or APX in roots and leaves inhibited.Furthermore,CAT did not affect the content of sugar,but the amount of proline and soluble sugar further rose in response to PTIO or DPI,thus significantly improved the capacity of osmotic adjustment.5.There was no significant effect of exogenous PTIO and CAT on the content of proline in wheat seedlings,but obvious increased in DPI-treated.The activities of ornithine aminotransferase(OAT),pyrroline-5-carboxylate synthetase(P5CS)and proline dehydrogenase(PDH)were decreased by the addition of PTIO,while PDH activity was decreased and P5 CS was not affected in root.CAT resulted in the reduction of OAT,P5 CS,PDH activities,but the root activity of OAT lower levels did not reach significant level.DPI induced the decreases of OAT in roots and leaves or P5 CS,PDH in leaves activities,but increases of P5 CS and PDH in roots.6.The content of Ca in leaves or Na in roots and leaves rose in PTIO-treated,whlie Ca and Mg reduced in roots.CAT resulted in the increase of Na in roots and leaves or Ca in leaves,but the content of K and Mg decreased in roots.DPI did not affect the content of K,Na or Mg in leaves,but significantly decreased the contents of Ca in roots and leaves or Mg in root.These results suggested that the generation of endogenous NO and apoplastic ROS influenced each other in wheat seedlings,especially that NO and apoplastic ROS effects the metabolism of reactive oxygen species and antioxidant enzymes,proline metabolism,which led to different oxidation response in the roots and leaves of wheat seedlings.