Effect Of Bagging On Wax Synthesis In Apple Fruit Epidermis

Wax is a kind of substance that exists in the surface of all terrestrial plants and is not easily soluble in water.Its main function is to prevent water loss and resist the invasion of pathogenic bacteria.Bagging can improve the external quality of fruit,but it can reduce the internal quality of fruit and affect the wax synthesis of fruit epiderm.Previous studies have been conducted on the formation of fruit quality by bagging,but there are few studies on the effect of bagging on fruit epidermal wax,and the effect of fruit bagging based on different light transmittance on the synthesis of apple epidermal wax is even less reported.Therefore,the effects of different fruit bags during the growth and development period on the wax structure,wax content and components,the concentration and gene expression of enzymes related to wax synthesis,postharvest weight loss rate and fruit quality of six-year-old Red ’Fuji’ and ’Tonami’ apples were determined.The main research results are as follows:1.The light transmittance,temperature and humidity inside and outside the white,single layer fruit bag(WB),yellow single layer fruit bag(YB)and double layer fruit bag(DB)were measured.The light transmittance of white single layer fruit bag was 48.21%,yellow single layer fruit bag was 32.71%,and double layer fruit bag was 0.The daily average temperature and humidity in the three fruit bags were not significantly different,but they were all higher than the control group.2.The fruit epidermal waxy structure was observed by scanning electron microscopy(SEM),60 days after full bloom,the fruit of cuticular wax coverage rate is low,only a small amount of short rod wax particles,late with fruit wax content increasing,the wax accumulated,to the fruit mature period(180 days after full bloom),apple fruit cuticular wax particles,form wax film.The epidermal wax of ’Tonami’ apple fruit is more than that of red‘Fuji’fruit and the wax film is thicker.Compared with CK,the epidermal wax was rough and not smooth,the wax film surface was uneven,and the epidermal wax layer was thin.The difference between DB and CK was the most obvious.3.Under the same site conditions,the total amount of epidermal wax and the proportion of each component of Red ’Fuji’ and ’Tonami’ apple fruits were different.With the extension of fru Red ’Fuji’ at the same period.180 days after full bloom,the total waxcontent of fruit epidermis of ’Tonami’ and Red ’Fuji’ CK were 992.43 μg·cm-2 and 536.08μg·cm-2 respectively,which were 85.13%higher than that of Red ’Fuji’CK.A total of 36 components were detected in the epidermal wax of ’Tonami’ apple fruits,and 29 components were detected in the epidermal wax of Red ’Fuji’ fruits.The carbon chain lengths of alkane compounds in the wax mainly distributed in the range of C16-C31.In Red ’Fuji’ apple,alkanes accounted for 35.56%-74.43%of the total wax,triterpenes accounted for 15.11%-32.23%;In ’Tonami’ apple,alkanes accounted for 31.06%-68.51%of the wax,triterpenes accounted for 15.21%-34.23%;Triterpenoids began to appear in the epidermal wax of Red ’Fuji’ apple 80 d after flowering,and triterpenoids began to appear in the epidermal wax of ’Tonami’ apple 100 days after full bloom.The total content of epidermal wax and aliphatic compounds increased with the increase of light transmittance,while the relative contents of aldehyde compounds and free fatty acids decreased with the increase of light transmittance.4.Bagging treatment decreased the concentration of KCS enzyme and the expression of wax synthesis related genes in apple fruit surface.During the whole fruit development period,the enzyme activity of KCS in WB,YB,DB treatments and CK pericarp all increased firstly and then decreased,and the activity of KCS in CK pericarp reached the maximum at 120 days after full bloom,and the concentration of KCS in CK pericarp was significantly higher than that of YB and DB.The relative expression levels of MdCER4 gene showed a trend of increasing,while the relative expression levels of MdCER6,MdCER10,MdKCS7/2,MdLACS and showed a trend of increasing first and then decreasing.The relative expression levels of MdCER6,MdCER10 and MdKCS7/2 were the highest at 100 days after full bloom.The expression levels of MdLACS and MdLTPG1 in the epidermis of Red ’Fuji’ apples reached the peak at 120 days after full bloom,while in ’Tonami’,the expression levels of MdLACS and MdLTPG1 reached the peak at 150 days after full bloom.5.Bagging increased the weight loss rate of postharveld fruits,and the weight loss rate of Dounan apples at room temperature was lower than that of Red ’Fuji’ apples.The weight loss rate of the same variety WB,YB and DB was higher than that of CK.The weight loss rate of Red ’Fuji’ apple fruits treated by WB,YB and DB was significantly higher than that of CK 6 days after storage at room temperature.The weight loss rate of’Tonami’ apple fruits treated by WB,YB and DB was significantly higher than that of CK 9 days after storage at room temperature.The brightness(L value)of DB treatment was significantly higher than that of WB,YB and CK,the soluble solid and sugar to acid ratio of bagged fruits were lower than that of CK,and the flesh hardness of bagged fruits was higher than that of CK.