| Tomato(Solanum lycopersicum)is the largest crop in protected cultivation,which plays an important economic role.However,tomato is vulnerable to low-temperature stress during winter protected cultivation,which seriously reduces the yield and quality of tomato.Grafting with rootstocks with strong stress resistance has been proved to be an effective method to improve crop stress resistance.Therefore,in this experiment,wild hairy tomato LA1777 with strong low temperature resistance was selected as rootstock,common cultivated tomato Jinpeng No.1(JP1)and ACT were grafted as scions,and JP1 and ACT were self-grafted,and four grafting combinations were obtained,namely JB1/LA1777,ACT/LA1777 and JB.The grafted seedlings were treated at 25℃/4℃(day/night),and the growth index,photosynthetic fluorescence parameters,nitrogen,phosphorus and potassium transport,active oxygen metabolism and expression levels of low-temperature related transcription factors were measured and analyzed,in order to further clarify the effect of LA1777 as rootstock on low-temperature resistance of tomato seedlings and explore the possible mechanism of improving low-temperature resistance.The main results are as follows:1.Under low temperature treatment at night,the growth of plant height,stem diameter,dry and fresh weight and root growth index of grafted seedlings with LA1777 rootstock were significantly higher than those of self-rooted seedlings,while the relative conductivity and malondialdehyde(MDA)of roots and leaves of grafted seedlings with LA1777 rootstock were lower than those of self-rooted seedlings,but the osmotic adjustment substances of leaves and roots,such as soluble sugar(SS)and root volume,were significantly higher.In addition,photosynthetic parameters and chlorophyll fluorescence parameters after low temperature treatment have better performance in grafted seedlings.The above results further confirm that LA1777 grafting as rootstock can significantly improve the low temperature resistance of seedlings.2.Through the determination and analysis of nitrogen,phosphorus and potassium in roots and leaves of grafted seedlings under low night temperature,it was found that the content of nitrogen,phosphorus and potassium in tissues of grafted seedlings of LA1777 rootstock was higher than that of self-rooted seedlings under low night temperature,and the accumulation of nitrogen,phosphorus and potassium in tissues and single plant was significantly higher than that of self-rooted seedlings with the extension of treatment time.In addition,during external treatment,the distribution rate of root system of grafted seedlings of LA1777 rootstock decreased,while the distribution rate of nitrogen,phosphorus and potassium in leaves increased.In addition,under low night temperature stress,the content and accumulation of nitrogen in grafted seedlings of LA1777 were more,but the changes of NRT1.1,AMT1.1,NR and GS1 were smaller,while those of NRT1.2,NRT2.1 and NRT2.3were higher than those of self-rooted seedlings.They worked together to maintain the nitrogen balance in grafted seedlings.Up-regulation of Le PT1 and Le PT2 in leaves of grafted seedlings of LA1777 significantly increased the activity of phosphate transporters in leaves,and then regulated the accumulation of phosphorus in various tissues of plants.Grafting LA1777 as rootstock can improve the activities of K+ channels and K+ transporters in leaves,maintain the concentration of K+ in leaves,and increase the accumulation of K+ in leaves,thus enhancing the low-temperature resistance of grafted plants.These results indicated that the grafted seedlings of LA1777 rootstock could alleviate the nutritional absorption barrier of tomato seedlings at low night temperature by maintaining high levels of nitrogen,phosphorus and potassium in leaves.3.Under low night temperature treatment,hydrogen peroxide and superoxide anion accumulated in roots and leaves of all treatments,but these two reactive oxygen species in leaves and roots of grafted seedlings of LA1777 rootstock were significantly lower than those in self-rooted seedlings.At the same time,the activities of non-enzymatic antioxidants(reduced ascorbic acid and glutathione)and antioxidant enzymes(including SOD,POD,CAT,APX,DHAR,MDHAR,GR,GST and GPX)in LA1777 were significantly higher than those in self-rooted seedlings.In addition,real-time fluorescence quantitative analysis showed that SOD1,SOD2,FESOD,CUZNSOD,CAT1,CAT2,CAT3,POD3,POD12,APX1,APX2,APX3,GR,DHAR,MDHAR and GST genes in grafted seedling leaves were differentially expressed at night low temperature,which affected antioxidant enzyme activity.These results indicated that the application of hairy tomato LA1777 could improve the scavenging ability of reactive oxygen species(ROS)and prevent lipid membrane peroxidation under low temperature stress,thus improving the low temperature resistance of grafted seedlings.4.Under night temperature stress,HY5 upregulation in the leaves of grafted seedlings of LA1777 rootstock induced CBF expression and then regulated the expression of antioxidant enzymes,thus improving the antioxidant capacity of grafted seedlings and making them have higher low temperature resistance.The expression of SAMDC,CHS and ACO genes showed that the grafting of LA1777 as rootstock might improve the cold tolerance of plants by promoting the biosynthesis of polyamines,flavonoids and ethylene.In addition,the grafting of LA1777 as rootstock can improve the expression of MYC2 transcription factor,and then the cold resistance of grafted seedlings can be improved by inducing the expression of flavonoid biosynthesis genes,polyamine biosynthesis and antioxidant related genes,and then accumulating flavonoids,polyamines and non-antioxidants and improving antioxidant enzyme activities. |
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