| Cucumber is one of the major vegetable crops grown in China,and in facility cultivation,it will encounter persistent cold and cloudy weather in winter and spring,which will be subject to low-temperature stress,resulting in a serious decline in its yield and quality.Cucurbita ficifolia is a unique melon resource in Yunnan with a variety of excellent traits such as cold tolerance and disease resistance.Grafting of Cucurbita ficifolia as rootstock is an effective measure to improve the cold resistance of cucumber in production.In this study,we used Cucurbita ficifolia as rootstock and Jing Yan Xia Mei No.2 cucumber as scion to simulate the low temperature of 15 ℃,10 ℃ and 5 ℃ in winter and spring in an artificial climate chamber to study the mechanism of cucumber grafted and self-rooted seedlings in response to low temperature in terms of growth and development,photosynthesis,osmoregulatory substances,antioxidant system and gene expression of antioxidant system.The effect of Yunna Cucurbita ficifolia rootstock on the cold tolerance of cucumber grafted seedlings was investigated to clarify the degree of cold tolerance of cucumber grafted seedlings and to provide reference for better selection of cucumber grafted rootstocks,so as to further elucidate the physiological and molecular mechanisms of grafting to improve the cold tolerance of cucumber.The main results of the study are as follows.1.Growth index measurement showed that the fresh weight,dry weight,plant height and stem thickness of Cucurbita ficifolia grafted seedlings,cucumber self-grafted seedlings and cucumber self-rooted seedlings were inhibited with the increase of low temperature stress,while Cucurbita ficifolia grafted seedlings were less affected by low temperature inhibition,indicating that grafting could alleviate the effect of low temperature stress and enhance the cold resistance of cucumber.2.The analysis of photosynthetic pigment content showed that the chlorophyll a content,chlorophyll b content and chlorophyll a+b content of leaves of Cucurbita ficifolia grafted seedlings,cucumber self-grafted seedlings and cucumber self-rooted seedlings decreased continuously with the increase of low temperature stress,and the chlorophyll a content,chlorophyll b content and chlorophyll a+b content of grafted seedlings were higher than that of self-rooted seedlings.The higher photosynthetic pigment content of Cucurbita ficifolia grafted seedlings indicated that Cucurbita ficifolia as rootstock could enhance photosynthetic function.3.The analysis of osmoregulatory substances showed that the contents of proline(Pro),soluble protein(SP)and soluble sugar(SS)in the leaves of Cucurbita ficifolia grafted seedlings,cucumber self-grafted seedlings and cucumber self-rooted seedlings increased continuously with the increase of low temperature stress,and the contents of proline(Pro),soluble protein(SP)and soluble sugar(SS)in grafted seedlings were higher than those in self-rooted seedlings,among which the changes of proline(Pro),soluble protein(SP)and soluble sugar(SS)in Cucurbita ficifolia grafted seedlings were higher than those in self-rooted seedlings.This indicates that Cucurbita ficifolia as rootstock can enhance cell stability,reduce the accumulation of osmoregulatory substances caused by low temperature stress,and enhance the cold resistance of cucumber.4.Analysis of electrolyte leakage rate and malondialdehyde(MDA)content of membrane lipid peroxidation products showed that with the increase of low temperature stress,malondialdehyde(MDA)and electrolyte leakage rate(EL)of Cucurbita ficifolia grafted seedlings,cucumber self-grafted seedlings and cucumber self-rooted seedlings continued to increase,and malondialdehyde(MDA)and electrolyte leakage rate(EL)of grafted seedlings were lower than that of self-rooted seedlings,indicating that grafting of Cucurbita ficifolia rootstocks The grafting of Cucurbita ficifolia rootstocks reduced the production of malondialdehyde(MDA)and electrolyte leakage rate(EL),and alleviated the damage to the cell membrane system of cucumber seedling leaves under low temperature stress.5.The analysis of antioxidant enzyme activities showed that the activities of superoxide dismutase(SOD),peroxidase(POD),catalase(CAT)and ascorbate peroxidase(APX)in the leaves of Cucurbita ficifolia grafted seedlings,cucumber self-grafted seedlings and cucumber self-rooted seedlings continued to increase with the increase of low temperature stress,and the activities of superoxide dismutase(SOD),peroxidase(POD),catalase(APX)in grafted seedlings),catalase(CAT)and ascorbate peroxidase(APX)activities of grafted seedlings were higher than those of self-rooted seedlings,while Cucurbita ficifolia grafted seedlings performed better,indicating that grafting of Cucurbita ficifolia rootstock could increase the activities of antioxidant enzymes in the leaves of cucumber seedlings under low temperature stress,thus maintaining intracellular redox homeostasis and reducing oxidative damage to cell membranes in cucumber seedlings under low temperature stress.6.The gene expression of antioxidant system showed that grafting can regulate the expression of related antioxidant enzyme genes,which may be a key factor in its ability to improve the antioxidant capacity of the crop.With the increase of low temperature stress,the expression of antioxidant system genes in Cucurbita ficifolia grafted seedlings,cucumber self-grafted seedlings and cucumber self-rooted seedlings leaves all showed an increasing trend,and the grafted seedlings had higher expression of antioxidant system genes than the self-rooted seedlings,and the grafted seedlings of Cucurbita ficifolia had higher expression of antioxidant system genes overall,indicating that Cucurbita ficifolia as rootstock can maintain a higher gene expression at the transcriptional level to make it regulate Antioxidant enzyme activity was elevated,which is an important reason for enhanced reactive oxygen species scavenging ability. |
