Primary Investigations On The Roles Of Plant Hormones And Active Oxygen Species Metabolisms During Senescence In Lettuce Detached Leaves

Endogenous phytohormone is microcontent material in plant but possesses important regulating physiological activity.And reactive oxygen species also play an important role by the process of the ripeness and senescence of fruit and vegetable.However,the interactive mechanism of plant hormone and active oxygen metabolism was not clear,In this paper, the relationship bewteen plant hormone and active oxygen metabolism in lettuce(Lactuca sativa L.) detached leaves during the senescence period were studied,PSK-α,6-BA and CPPU,Ethephon,AgNO₃,H₂O₂ and AsA were used to treat lettuce detached leaves, Understanding of the relationship is helpful for us to uncover the mechanism of lettuce detached leaves senescence and to regulate leaves senescence.The main results were as follows:1.Exogenous PSK-α,6-BA,CPPU,AgNO₃ and AsA treatments to some extend can slow down the degraded rates of soluble protein and chloroplast in lettuce leaves, possessing a positive modulating function.However,Ethephon and H₂O₂ play a reversed role,accelerating the degraded rate of soluble protein and chloroplast from lettuce leaves, having a negative modulating function.Moderate concentration of PSK-α(3 nmol/L) could significantly inhibit the senescence speed of leaves,but the lower or higher concentration was showed no inhibitation.6-BA and CPPU could conspicuously inhibit the degradation of chloroplast after the treatment of 48 h.and the degradation of protein was well inhibited during the treatment of 48 h-72 h by PSK-α.The sample treated with AgNO₃ had a higher characteristics value than contrast.AsA can maintain the leaves with more protein rather than chloroplast.Ethephon can decrease the amount of chloroplast,but it had little effects on the soluble protein after 96 h.H₂O₂ could accelerated the degradation rate of chloroplast and soluble protein,so their examined values were lower than control..2.Exogenous PSK-α,6-BA,CPPU,AgNO₃ and AsA,all of them could protect the cell's membrane structure from damage,and the average electronic conductive rate of lettuce leaves were lower than that of contrast.Ethephon and H₂O₂ would destroy the structure of cell membrane and stimulus the production of MDA.but PSK-αand AsA could decreased the MDA content.And other treatment towards sample caused very complicated changes on the MDA content.The treatment with 6-BA and CPPU could decline the oxidation of lipid within 72 h.After 72 h the MDA content in the sample rised compared to contrast. AgNO₃ could decreased MDA content in the first 30 h,but it could increased MDA content,compared to contrast during the last 30 h.3.Study on different treatments correlated with ROS metabolism factors,eg.H₂O₂ content,CAT,APx and SOD activity.We found that exogenous PSK-α,6-BA,CPPU, AgNO₃ and AsA can enhance protective enzyme activity,and they can lead to low down the amount of ROS,however different treatment has different results.Low concentration of PSK-αand AsA inhibited H₂O₂ producing.Ethephon and H₂O₂ enhanced endogenous H₂O₂ producing,but other treatment have complex effects on H₂O₂ content.High concentration of PSK-αhave little effects on H₂O₂ in early time(24 h).But after 48 h it promoted H₂O₂ producing.6-BA and CPPU have a little effect on H₂O₂ producing on detached lettuce leaves.AgNO₃ promoted H₂O₂ producing them before 48 h,after 48 h inhibited H₂O₂ producing before 48 h.Result reavealed that H₂O₂ is a probably important factor leading to leaf senescence.PSK-α,6-BA,CPPU can enhance CAT and SOD activity,but ethephon and H₂O₂ can degrade.AsA and enhance CAT activity,AgNO₃ degrade CAT activity.But after 72 h CAT's activity raised quickly.H₂O₂ and AsA have a little effect on SOD activity.AgNO₃ stimulate SOD activity.Low concentration of PSK-αhave little effects on APx activity.But high concentration of it can delay APx activity's depression.The APx activity of 6-BA and ethephon treated leaves speed up rapidly. When the leaves were treated by CPPU,its APx activity of were lower than that of control before 48h.but during 48 h-72 h that exceed the value of control.The APx activity in AgNO₃ treated leaves was lower than that in control.H₂O₂ and AsA have a little effect on APx activity which were lower than control before 48 h but then have a little rise.4.Effect of different treatments on endogenous hormone in lettuce leaves were studied. we found that exogenous PSK-α,6-BA,CPPU,AgNO₃ and AsA can inhibit exogenous ZRs,iPA of CTK content.But Ethephon and H₂O₂ have opposite effect.In generally physiology metabolism process the CTK decreased along with senescence.H₂O₂ and AsA have effect on endogenous CTK content on the time of regulating plant senescence.It is necessary to research on the specific mechanism.PSK-α,6-BA,CPPU,AgNO₃,AsA and H₂O₂ which can inhibit ethylene producing mechanism.Hence they can decrease protective enzyme activity and speed up protein degradation,We can infer that H₂O₂ inactivity on enzyme on the ethylene signal transmission.It is thus clear that ROS influence enzyme in hormone metabolism.