Regulation By Nitric Oxide On Mitochondrial Functions And Oxidative Damage In Peach Fruit

Peach is a kind of typical respiration climacteric fruit,the significant increase in respiration intensity causes the accumulation of reactive oxygen species(ROS)in peach fruit,which leads to the softening and browning of fruits,resulting in the decrease of commodity and nutritional value.The appearance of respiration climacteric marks the maturity of the fruit,and it also means the beginning of the aging of cells and even the whole fruit.Coincidentally is that mitochondrial oxidative damage is a major factor that accelerates aging and death of cells,thus,it is really important to alleviate the mitochondrial oxidative damage to maintain the quality of postharvest peach fruit.As a biological signaling factor,nitric oxide(NO)can defense excessive ROS by activating the antioxidant systems to remove them directly.Moreover,appropriate concentration of NO is thought to protect mitochondria in different pathways correlated with respiratory control and apoptosis.This experiment is based on the‘Xintai hong'peach fruit as materials,using double distilled water(control),15?mol?L^-1 NO solution or 5?mol?L^-1 c-PTIO(NO scavenger)solution to soak the peach fruit,and storage at 0?.The effects of different treatments on the storage quality of peach fruit,mitochondrial functions,mitochondrial DNA(mt DNA)oxidative damage,and a key factor for DNA replication-PpPrimPol were studied.Results were as follows:(1)NO treatment could effectively delay the decrease in the pulp color L*value and the firmness,so as to relieve the browning and softening of postharvest peach fruit.And NO treatment delayed the increase in soluble solids content and respiration rate,therefore,it could reduce the consumption of energy and nutrients.Low temperature storage also reduced the evaporation of water caused by transpiration,thus inhibiting the increase in weight loss rate.(2)NO treatment could sustain the higher mitochondrial membrane potential and delay the decrease in the activities of complex?-?and alternative oxidase in the mitochondrial respiratory electron transport chain,so it maintained efficient operation of cytochrome pathway and alternative pathway in the respiratory electron transport chain,and thus inhibiting the mitochondrial ROS production.In the meantime,NO treatment increased the activity of NAD(P)H dehydrogenase on both sides of mitochondrial inner membrane,thus maintaining the redox balance between inner and outer sides of the mitochondrial inner membrane.And NO treatment sustained the relatively low level of mitochondrial cytochrome c content and complex?activity,thus reducing the mitochondrial oxygen consumption and inhibiting cell apoptosis.(3)NO treatment promoted the operation of the tricarboxylic acid cycle by raising the activities of the citrate synthase,pyruvate dehydrogenase complex,fumarase,succinate dehydrogenase and other related enzymes in mitochondrial tricarboxylic acid cycle,which met the needs of the plant to increase carbon skeleton and provided ample substrates for the mitochondrial respiratory electron transport chain.Moreover,NO treatment could reduce the oxidative stress and maintained the integrity of mt DNA.(4)NO treatment could effectively delay the reduction of mt DNA copy number,thus maintaining the stability of mt DNA genome.In addition,NO could effectively reduce the mitochondrial ROS content,thereby down-regulating the level of 8-hydroxy-2'-deoxyguanosine(8-OHd G)in mt DNA.(5)NO treatment could up-regulate the expression level of PpPrimPol,thereby promoting the process of DNA replication.The complete encoding sequences of PpPrimPol was cloned by PCR and other techniques,it contains 1,764 bases and encodes 587 amino acids.