| Tomato(Solanum lycopersicum L.),also known as tomato and tomato,belongs to one-year-old or perennial herbaceous plants of Solanaceae.Its edible and medicinal values are prominent and widely distributed in the world,and it is one of the important vegetable crops of“ South-to-North ”and“ West-to-East ”in China.However,during the whole growth period of tomato,especially the seedling stage,it is very sensitive to water deficit and vulnerable to drought,which seriously hinders the production and planting of tomato.Therefore,it is particularly important to study the resistance mechanism of tomato to drought stress and explore effective ways to improve the drought resistance of tomato seedlings for ensuring the development of tomato production.In this study,tomato ’ Xidayinghong No.1 ’ was used as experimental material.Tomato seedlings were planted in greenhouse,and the pretreatment was started when the four leaves were in one heart.By controlling the water content in the growth process and simulating natural drought conditions,the apparent morphology of tomato was observed,and the microstructure characteristics of tomato were studied by paraffin section method.The physiological and biochemical indexes of tomato were determined,and the expression of antioxidant enzyme genes in tomato seedlings was detected by real-time fluorescent quantitative PCR.In order to further understand the drought resistance mechanism of tomato and the role of exogenous salicylic acid and melatonin in the process of drought stress of tomato from the perspectives of morphological structure,cell physiology and molecular,and provide certain reference value for subsequent tomato production and breeding and high-quality cultivation research.The main results of this study are as follows :1.Exogenous SA and MT treatments could alleviate the inhibition of drought stress on the growth and development of tomato seedlings.Under drought stress,the growth of plant height and stem diameter of tomato seedlings decreased significantly,but the chlorophyll SPAD value of leaves increased.The thickness of blade became thinner,the thickness of palisade tissue,the thickness of spongy tissue and the porosity of blade structure decreased,and the fence-sea ratio increased.Tomatoes adopt the ’ saving ’ strategy to adapt to water deficit,that is,by increasing the grid-sea ratio,reducing the contact area between plants and the outside world,reducing damage,and maximizing water conservation and utilization.The growth of plant height and stem diameter were increased after exogenous SA and MT treatment,and the water retention and drought resistance of tomato leaves were improved to some extent.2.Under drought stress,leaf relative water content decreased,reactive oxygen species accumulated,resulting in cell membrane oxidative damage;at the same time,the content of osmotic adjustment substances in tomato seedlings increased.After pretreatment with exogenous SA and MT,the antioxidant system of tomato seedlings responded rapidly,increased the activities of SOD,POD,CAT and APX,decreased the content of reactive oxygen species,and avoided membrane peroxidation damage.The increase of antioxidant enzyme activity and the accumulation of osmotic adjustment substances enhanced the water retention and drought resistance of tomato seedlings to a certain extent.3.Under drought stress,the expression of antioxidant enzyme genes Cu/Zn-SOD,CAT1 and APX2 in tomato seedlings decreased.Exogenous spraying salicylic acid and melatonin increased the expression of Cu/Zn-SOD,CAT1 and APX2 genes in tomato seedlings under drought stress.At the same time,the variation trend of gene expression and enzyme activity is not necessarily consistent,which may be due to the influence of genes,stress time or other unknown pathways on the regulation of enzyme activity. |
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