Study On The Way Of DA-6 Improving The Resistance Of Tomato Seedlings To Low Night Temperature

Tomato(Solanum lycopersicum),as an kind of warm-climate vegetables,is easy to be damaged by low temperature at night in winter and spring when it is planted in the greenhouse.In the past thirty or forty years,many methods have been used to improve the cold tolerance of tomato,such as applying exogenous materials and cultivating cold resistant varieties.Compared with the currently widely used exogenous substances,DA-6 is more cheaper and safer,and can be naturally degraded under natural conditions,with less residues,no toxicity and the phenomenon of yield increase but quality deterioration.In recent years,it has been reported that exogenous spraying of DA-6 can promote the growth and development of tomato,improve the quality of fruit,and improve the cold tolerance of tomato plants,but the research only stays at the physiological and biochemical level,but it is not clear how to improve the plant resistance.In my experiment,the tomato variety "liaoyuanduoli" was used as the test material to do the low night temperature treatment,and to explore the regulation of DA-6 to improve cold tolerance of tomato plants.The main results of this test are as follows:1.The optimum DA-6 concentration for improving cold tolerance of tomato was determined.Under the low night temperature stress,the tomato plants pretreated with 10mg/L DA-6 had the best growth potential,the largest leaves,and the plant height and stem diameter were higher than those pretreated with other concentrations.At the same time,under the pretreatment of 10 mg/L DA-6,the brown of leaves was the lightest,and the content of H2O2 was the least.DA-6 of 5 mg/L,10 mg/L and 20 mg /L effectively reduced the effect of low night temperature stress on the photosynthesis of tomato plants,and Pn,Gs,Ci,Tr values increased compared with water spray plants.Therefore,10mg/L was selected as the best DA-6concentration to improve the cold tolerance of tomato plants.2.DA-6 alleviated photosynthesis of tomato leaves at LNT.Compared with LNT treatment,the content of chlorophyll a,chlorophyll b,chlorophyll a/b was significantly increased after LNT+DA-6 treatment.And there was no significant difference in the contents of chlorophyll b and carotenoid under DA-6,they were higher than those of LNT.Meanwhile,Compared with LNT,the coding genes of almost all related enzymes in the chlorophyll synthesis pathway NYC1,HCAR,PAO,RCCR,HO,PIF4,NAO16,EEL,FC1 and FC2 decreased significantly in LNT+DA-6,which indicated that DA-6 could promote the synthesis of chlorophyll in tomato plants under low night temperature stress,inhibit its decomposition,increase chlorophyll content,enhance photosynthesis and improve cold tolerance.3.It was clear that DA-6 could alleviate PSII photochemical activity of tomato leaves at low night temperature.Compared with LNT treatment,LNT + DA-6 treatment significantlyincreased Fv/Fm,Y(II),ETR(II),but significantly inhibited Y(NPQ),NPQ,while the changes between q P and 1-qp treatment were significant,but there was still a trend of increasing and decreasing in numerical value.At the same time,under LNT + DA-6 treatment,the expression of Psb A,Psb B,Psb C,Psb D and Psb P genes were all significantly increased,which indicated that exogenous DA-6 promoted the expression of D1,D2 protein and core antenna coding gene of OEC,which is the oxygen releasing complex of PSII under low night temperature stress,at the same time,it stabilized PSII complex and ensured the normal photosynthesis.4.DA-6 alleviated the PSI activity of tomato leaves at low night temperature.Under LNT stress,Y(NA)decreased significantly and Y(ND)increased significantly,indicating that the main reason for the decrease of PSI activity under low night temperature stress is the donor side limitation of PSI.Compared with LNT treatment,PS(I),ETR(I),Y(NA)were significantly higher and Y(ND)was significantly lower under LNT + DA-6 treatment.After DA-6 pretreatment,the genes of Psa A,Psa B,Psa C,Psa D and Psa L were significantly increased compared with LNT,and the multiple of increase was between 2.2-8 times.DA-6pretreatment increased the expression of PSI complex related genes,indicating that DA-6pretreatment can stabilize the structure of PSI,significantly alleviate the donor side restriction of PSI,and alleviate the phenomenon of excess light energy absorbed by psi.In addition,LNT+ DA-6 significantly alleviated the accumulation of H2O2 and O2-in tomato leaves,which indicated that DA-6 pretreatment could enhance the ability of active oxygen scavenging and plant resistance.5.DA-6 maintained the ultrastructure of chloroplast in tomato leaves at low night temperature.In this study,compared with CK treatment,the chloroplast of tomato leaves was gradually decomposed,the hloroplast was obviously expanded,nearly spherical,and the length of chloroplast decreased in numerical value.At the same time,the low night temperature stimulated the width of chloroplast,and its length / width decreased significantly.At the same time,the chloroplast like capsule membrane was degraded,and the hungry particles diffused into the cytoplasm,meanwhile,the starch grains increased and hungry particles appeared Under the treatment of LNT+DA-6,the leaf chloroplast expansion was alleviated obviously.6.Make clear that DA-6 regulates the hormone content of tomato leaves under low night temperature.Compared with LNT,DA-6 pretreatment reduced ABA but had no significant change,ZR increased significantly.At the same time,under LNT + DA-6 treatment,the synthesis genes IPT3,IPT4 and IPT5 of ZR were significantly increased,and the decomposition genes CKX2,CKX3,CKX4,CKX5 and CKX7 were all significantly down regulated.On the other hand,compared with the LNT treatment,the expression of AAO,ABA2,NCED4,ZEP1,CYP707A1,CYP707A2 and ABI5,MYB1,AREB the related genes of signal transmission,were significantly up-regulated.7.DA-6 induced the expression of cold stress related genes under low night temperature stress.Compared with LNT treatment,CBF1 increased significantly under LNT+DA-6treatment for 6-12 days,CBF2 showed a similar change trend,while CBF3 increased significantly in 0-6 days,and then decreased.