The Ralationship Between Fruit Cracking And Reactive Oxygen Or Cell Wall Metabolism In Different Parts Of Tomato Fruit

Tomato(Lycopersicon esculentum Mill.)is one of the most widely cultivated vegetables in the world with higher commercial value.It also serves as a good model crop for fruit development.However,cracking phenomenon occurred easily in tomato fruit when the environmental conditions are not suitable.Fruit cracking will affect the appearance and quality of fruits,and it will also cause serious impact on production Therefore,it is of great significance to investigate the mechanism of fruit cracking in tomato.When there is a rapid liquid flow into the fruit,for mature or other reasons led to the peel strength and elasticity decreased,which will led fruit cracking,and tomato fruit cracking often occurs in the turning and red ripe stage.Active oxygen metabolism disorders,tissue aging,cell wall degradation,cracking rate will gradually increase during fruit ripening.But in tomato,the relationship between the fruit cracking and active oxygen or cell wall metabolism have been rarely reported.In addition,fruit cracking usually starts from a specific area,so there may be differences in the activity of oxygen metabolism and cell wall composition in the different parts of the peel.The former study often studied peel as a whole,however,rare reports has studied the different parts of the peel.In this experiment,in order to study the relationship between fruit cracking and active oxygen or cell wall metabolism,we used the cracking-resistant tomato and susceptible tomato as plant material.1.In order to study the relationship between characteristics of active oxygen metabolism and fruit cracking,the genetrative rate of superoxide anion radial and the content of hydrogen peroxide,the degree of membrane lipid peroxidation,the activity of the antioxidant enzymes,antioxidant substance(AsA)content and the content of soluble protein in the different parts(top,middle and bottom)of cracking-resistant tomato material and susceptible tomato material at different growth stage(mature green stage,turning stage and red ripe stage)were studied.The studies showed that,the top of the fruit had higher active oxygen content and the degree of membrane lipid peroxidation than the middle and the bottom of the fruit.At the late stage of fruit development,cracking-susceptible tomato had higher active oxygen content and the degree of membrane lipid peroxidation than that of cracking-resistant tomato in the same part.The activity of the antioxidant enzymethes(SOD,GR,APX)and the content of antioxidant substance(AsA)of susceptible tomato in the same part were all lower than that of cracking-resistant tomato.The disorder of active oxygen species metabolism led to higher membrane peroxidation degree in cracking susceptible tomato in the top of the fruit,and further accelerated senescence of fruit,which could be one of the reasons that led to the occurrence of fruit cracking at the top of the fruit.2.To reveal the relationship between characteristics of active oxygen metabolism and fruit cracking in the pericarp and mesocarp of tomato fruit,we used cracking-resistant tomato and susceptible tomato in the red period as test materials.The genetrative rate of superoxide anion radial and the content of hydrogen peroxide,the degree of membrane lipid peroxidation,the activity of the antioxidant enzymes,antioxidant substance(AsA)content and the soluble protein content in different parts(top,middle and bottom)of cracking-resistant tomato material and susceptible tomato material at different growth stage(malure green stage,turning stage and red ripe stage)were studied.The studies showed that,the pericarp of the fruit had higher active oxygen content and the degree of membrane lipid peroxidation than in the same part of the mesocarp of the fruit;the top of the pericarp had higher active oxygen content and the degree of membrane lipid peroxidation than in the middle and the bottomm of the fruit.The pericarp of susceptible tomato higher active oxygen content and the degree of membrane lipid peroxidation than than that of cracking-resistant tomato in the same part at red ripe stage.The activity of the antioxidant enzymethes(SOD,GR,APX)and the content of antioxidant substance(AsA)of cracking susceptible tomato in the same part were all lower than that of cracking-resistant tomato.In conclusion,it may be the pericarp of the top of the susceptible tomato had higher membrane peroxidation degree and active oxygen species metabolism than that of cracking-resistant tomato,which due to cracking occured from the top of the fruit,and the degree of fruit senescence in the pericarp played an important role in fruit cracking occured.3.To reveal the relationship between cell wall components or enzyme activies and fruit cracking,we used cracking-resistant tomato and susceptible tomato as test materials.The content of pectin,cellulose and hemicellulose,the activity of PG,β-glucosidase,PPO,and Cx in different parts(top,middle and bottom)of cracking-resistant and susceptible tomato at different growth stage(mature green stage,turning stage and red ripe stage)were studied.The studies showed that,soluble pectin content and the activity of PG and PPO in the top,middle and bottom of fruit showed a trend of increasing,insoluble pectin,hemicellulose and cellulose content showed declining trend,and the activity of cellulase and β-glucosidase showed first increased and then decreased during fruit ripening.The middle of the fruit had higher soluble pectin content,higher level of PG,cellulase andβ-glucosidase,lower level of insoluble pectin,hemicellulose and cellulose content than the top and bottom of the fruit.The activity of PPO in the top was higher than than in the middle and the bottom of the fruit.Cracking-susceptible tomato had higher soluble pectin content,higher level of PG,cellulase,p-glucosidase and PPO activity,and lower level of insoluble pectin,hemicellulose and cellulose content than that of cracking-resistant tomato in the same part,the cell wall component degradation rate in the middle of fruit was higher than the top and the bottom,and cell wall extension in the top end was higher than the middle and bottom.It was possible that combination part between of the top and the middle was the position where cracking started and then spread to other parts of the tomato fruit.