Effectsofbagging On Fruit Coloration In Different Apple Cultivars

Color is an important indicator for the quality of fruit appearance.While in apple producing areas of the LoessPlateau,due toits unique climatic conditions,non-red cultivars can also be colored after bagging trement.In order to explore the reason of colordifference under the conditions of light stress induced by bagging in different applecultivars,‘Granny Smith',‘Golden Delicious' and ‘Red Delicious' were used as experimental materials.The effect of bagging on fruit colorcondition and changes of the related indexes of light stress were studied.The effect of light stress on fruit coloring was analyzed.At the same time,the methylation level of MdMYB1 gene promoter region in ‘Granny Smith' was measured on the basis of optimizing DNA extraction method,and the effect of DNA methylation on fruit color was discussed.The main results as follows:1.Three different apple cultivars could be induced coloring after bagging trement,but the color degree performanced quite different.After bag removal,the color parametersbrightness value L*,yellowish value b*,hue angle h° decreased,the redness value a* value increased,the color saturation C* value decreased first and then increased in three apple cultivars,and the peel color gradually became red.The results showed that the content of chlorophyll and carotenoid in bagging fruits was significantly lower than that of unbagging fruits,which indicated that shading could inhibit the synthesis of chlorophyll and carotenoid.Ten days after bag removal,fruit color was very different in three cultivars.The ‘Red Delicious' fruit color was almost the same between bagging and unbagging fruits,both of them was dark red and the anthocyanin content was about 0.8 mg/g.No anthocyanin was detected in ‘Granny Smith'and ‘Golden Delicious' unbagging fruits,and the fruit was green and yellow respectly.Anthocyanin content in‘Granny Smith'was 0.14 mg/g,and the content in‘Golden Delicious' was less,only 0.03 mg/g.The fruits Varied degrees of red.2.The effect of bagging on the light stress of different color cultivars was different.After bag removal,the reactive oxygen species content and the activity of antioxidant enzymes were significantly lower in bagging fruits than those unbagging.The reactive oxygen species content increased first and then decreased in the three apples,but the content was differentamong different cultivars.The content in ‘Granny Smith' was the highest,followed by ‘Golden Delicious' and ‘Red Delicious' was the lowest.The activities of SOD,APX,CAT and POD antioxidant enzymes also increased first and then decreased after bag removal.Thecorrelation between the reactive oxygen species content and anthocyanin accumulation showed that there was a significant difference in three cultivars.The correlation of ‘Granny Smith' was big,and it was possible that the light stress could play an important role in the induction of anthocyanin synthesis.The correlation of ‘Golden Delicious' was lower than that of ‘Granny Smith',suggesting that the induced effect of light stress on anthocyanin was small.Thereactive oxygen species content in ‘Red Delicious' was low,but the anthocyanincontent increased rapidly.The light stress might have little effect on the induction of anthocyanin synthesis.3.In order to study the effect of DNA methylation on fruit coloring,the extraction of fruit genomic DNA was the first step.Based on the characteristics of apple fruits rich in polysaccharides and polyphenols,three kinds of DNA extraction methods were compared and the extraction scheme was optimized.The results showed that the method three was the best,adding the interfering solution before the nuclear cleavage,increasing the concentration of ?-mercaptoethanol and PVP and adding NaAC,which could effectively remove polysacch-arides,polyphenols and other secondary metabolic substances.DNA extracted by this method can be used for molecular biology experimental analysis.4.The methylation level of MdMYB1 promoter region(-2026bp~-1870bp)was analyzed by bisulfite sequencing(BSP)in ‘Granny Smith'fruits.The results showed that the region was lower in ten days after bag removal fruits than that of unbagging fruits,indicating that DNA methylation might have an important effect on ‘Granny Smith' fruit color.