Study On The Role Of Tissue Senescence In The Type Of Cracked Fruit During Tomato Ripening

Tomato(Solanum lycopersicum)is an important economic crop and is also recognized as a model crop for fruit development.Cracking is a common problem in protected and open field production.Once the fruit has cracked,it will become extremely vulnerable to pathogens and insects,which will lead to fruit rot and deterioration,and seriously affect sensory quality,reduce market sales capacity,and cause huge economic losses.Among the many types of tomato cracking,ring-cracking and radial-cracking are two common types and research is concentrated.In recent years,studies have found that fruit tissue senescence seems to be another important factor leading to fruit cracking.Unbalanced reactive oxygen species metabolism a nd increased membranous peroxidation are important motivations of tissue senescence.When the plasma membrane system was severed,it will lead to cell death,which will affect the balance of the fruit's sudden injection of water during the ripening stage,and then cause fruit cracking.In summary,three tomato varieties with cracking-resistant,ring-breaking and radial-cracking were selected to study the equilibrium mechanism of reactive oxygen species metabolism and the degree of membrane peroxidation in t he pericarp and flesh of different parts of the fruit during ripening stage.At the same time,the relationship between cell death and fruit cracking was further explored.The main findings are as follows:(1)In order to reveal the relationship between the characteristics of reactive oxygen species metabolism and fruit cracking,pericarpand and flesh's reactive oxygen species content,antioxidant enzyme activity,anti-oxidant substance content and membrane peroxidation degree of cracking-resistant variety(17922),ring-cracking variety(16750)and radial-cracking variety(16620)in different parts(fruit shoulder,fruit belly,and fruit top)during the ripening process(green stage,turning stage,and red ripe stage)were studied.The results showed that compared with the cracking-resistant variety 17922,the ring-breaking variety 16750 and the radial-cracking variety 16620 had low antioxidant enzyme activity(except POD),low antioxidant substance content,high degree of membrane peroxidation,maladjustment of reactive oxygen species metabolism and aggravation of senescence in the fruit shoulder pericarp during the turning stage and red ripe stage.This trend in the flesh was not as dramatic as it occured in the pericarp.(2)Using TUNEL and DAPI double staining and DNA Ladder combination method to detect the programmed cell death of the pericarp at fruit shoulder during ripening stage.The results showed that during the maturation process,compared with the cracking-resistant variety 17922,the susceptible cracking varieties(16750,16620)slightly increased the programmed cell death in the red ripe stage;DNA Ladder was detected during the ripening process.It was found that none of the three varieties had ladder-like bands,and the dead cells were not concentrated in the cracks,indicating that cell death was not the cause of the cracks.(3)Transmission electron microscopy was used to observe the morphological changes of pericarp cells in the cracking part,uncracked part,imminent cracking part in fruit shoulder during the ripening stage.The results showed that the changes of organelles in the cells of the cracking-resistant variety 17922 and the susceptible cracking varieties(16750,16620)were mainly concentrated in stage from fruit turning stage to red ripe stage,and the early phenomenon of programmed cell death occurs earlier in susceptible varieties than in cracking-resistant variety 17922.However,the cell morphological changes of the radial-cracking variety at the same time were faster than those of the ring-cracking variety(16750).(4)According to the above results,three reactive oxygen scavenging enzyme gene: Sl APX1,Sl CAT1,Sl FER1,and reactive oxygen species producing gene Sl RBOH were selected in this study.Using q RT-PCR technology to detect the expression levels of the genes of pericarp cells in the cracking part,uncracked part,imminent cracking part in fruit shoulder during the ripening process.The results showed that the expression of reactive oxygen scavenging enzyme genes in susceptible cracking varieties(16750,16620)was higher than that in cracking-resistant variety 17922 during the green stage,and the expression of Sl RBOH gene was lower than that in cracking-resistant variety 17922,indicating that the imbalance of reactive oxygen species metabolism had occurred in the green stage.Except for Sl CAT1,the trend of the expression of each gene in the turning stage and red ripe stage of the susceptible cracking varieties(16750,16620)was cracking part < imminent cracking part < uncracked part;Sl CAT1 shows cracking part < uncracked part < imminent cracking part.It was suggested that Sl APX1,Sl FER1 and Sl RBOH was more involved in the stress before fruit cracking,while Sl CAT1 was associated with fruit cracking.