The Effect Of Phosphorus Application On Respiratory And Mitochondrial Defense Pathways Of ROS In Fargesia Roots Under Drought Stress

As one of the most serious abiotic stress factors,drought vastly limits the growth,productivity and natural regeneration of plants.With the increasing of frequency,intensity and region in drought,it is inevitable to brought about serious influences in the natural regeneration of Fargesia,which will cause a shortage of food for giant panda.Besides,drought also significantly reduces the effectiveness of phosphorus that is considered as the most important element in plant growth and development.With the rapid growth of arrow bamboo,it is easy to make phosphorus deficiency in the soil.In the meantime,it will seriously impact the natural regeneration of arrow bamboo.However,the study of drought response and the mechanism of phosphorus control is rarely reported.Moreover,the respiratory metabolism of root,as the first part to feel the soil drought,plays an important role in adaptation to drought.But it is infrequent noticed on woody plants.Toward this end,the project regards Fargesia roots as the research object,studying on the physiological and molecular mechanism of the bamboo roots on drought response and phosphorus regulationl from the perspective of respiratory metabolism and mitochondrial reactive oxygen scavenging.Main results are as follows:1.Under drought stress,the effects of phosphorus application on active oxygen and membrane lipid peroxidation in therootswere studied.The results showed that the superoxide anion(O2-·)production rate and hydrogen peroxide(H2O2)content increased significantly by drought stress,Therefore,the content of Malondialdehyde(MDA),which represents the peroxide degree of membrane lipid,was significantly increased in the roots.However,phosphorus application reduced the production rate of O2-· and H2O2 content in roots,especially H2O2 content.Meanwhile,the MDA content of the roots was significantly decreased.Therefore,phosphorus application reduced the oxidative damage of Fargesia roots.2.Under drought stress,the effects of phosphorus application on respiratory metabolism in the roots were studied.The results showed that the total respiration rate and cytochrome respiration rate were cut down by drought stress.Moreover,the key enzyme of cytochrome pathway COX activity and the relative expression level were also decreased.Hence,drought stress caused a large number of ROS damage to mitochondrial function.At the same time,the alternation respiration rate of the mitochondria in the roots was improved by drought stress.The relative expression level of AOX gene was significantly enhanced that could reduce the production of ROS in Fargesia roots under drought stress and it has certain drought resistance.The phosphorus application significantly increased the relative expression level of AOX gene and pyruvate content,as well as the mitochondrial alternate respiration rate was further improved.These could significantly cut down ROS production and membrane lipid peroxidation in Fargesia roots under drought stress.Meanwhile,as the COX activity and the relative expression level of genes were increased,the total respiration rate and cytochrome respiration rate also increased.In addition,drought stress significantly reduced the activities of six key enzymes and relative gene expression levels in EMP and TCA pathways,however,phosphorus application slowed down the activities relative expression and levels of the six enzymes in the two pathways,as could reduce the degree of obstruction of the EMP and TCA pathways.Whereas,the activity and gene expression levels of 6-P-GDH and G-6-PDH were significantly increased by drought stress.And the drought stress increased the pentose phosphate pathway in Fargesia roots so that it has certain drought resistance.The phosphorus application was significantly increased the activity of 6-P-GDH and G-6-PDH and the relative expression level of gene which were under drought stress,significantly increasing the pentose phosphate pathway in t Fargesia roots.Therefore,phosphorous application could reduce the oxidative damage of Fargesia roots under drought stress by improving alternate respiration pathway and the pentose phosphate pathway.3.Under drought stress,the effects of phosphorous application on the antioxidant system in the mitochondria of Fargesia roots were studied.The results showed that drought stress significantly increased the activity of antioxidant enzymes(SOD,APX,MDHAR,DHAR and GR)in the mitochondria of Fargesia roots.In general,the relative expression levels of these antioxidant enzymes were also enhanced,It also increased the contents of AsA and GSH,helping reduce the accumulation of ROS in the mitochondria of Fargesia roots under drought stress and oxidative damage so that it could survive.The application of phosphorous application increased most of the antioxidant enzyme(SOD,APX,MDHAR and DHAR)activity in the mitochondria,especially MDHAR.It also significantly increased the relative expression level of most antioxidant enzymes(SOD,APX,DHAR and GR)and AsA content.These could significantly reduce the accumulation of ROS and the damage of membrane lipid peroxidation.Hence,phosphorous application could improve the drought resistance by improving the antioxidant system to reduce the oxidative damage of Fargesia roots under drought stress.