| Mango (Mangifera indica L.) is a typical respiratory climacteric tropical fruit,which is full of nutritional value and high economic value. Gibberellin (GA) is one of the plant hormones that regulates the growth and development of plants. It has many positive effects in the growth of fruiter, fruit color development, quality formation and storage preservation.It is widely used in the agricultural production. There are more than 100 kinds of GA which have been isolated and identified. Among them, GA3 has the strongest physiological activity and is distributed widely. Color is one of the important appearance quality traits of fruit, and pre-harvest GA3 treatments have important influence on fruit color development.In this paper, the main varieties of ’Guifei’ and ’Tainong No.1’ mangoes with pre-harvest GA3 treatments were used to study the effects of GA3 on changes in storage quality,pigment content, enzyme activities and related gene expression. The intrinsic relationships between exogenous GA3,fruit storage quality, color development and endogenous GA3 were discussed. The results are as follows:(1) In the different stages of fruit development (flowering period, young fruit period,fruit enlargement period), the effect of different GA3 concentrations (0, 0.5, 1.0, 2.0, 3.0,4.0g/L) treatment on the storage quality and pre-harvest physiology were studied by using the 10-years-old ’Guifei’ mango trees as the experimental material. The results showed that,compared with CK, the low concentration of GA3(0.5, 1.0, 2.0g/L) could maintain high fruit hardness and inhibit the accumulation of malondialdehyde (MDA) ,Total Soluble Solid(TSS),Vitamin C (Vc) and Total Acid (TA),slow down the growth of a*,inhibit the degradation of chlorophyll and carotenoids and anthocyanins accumulate, and reduce the activity of Chlorophyllase (Chlase), phenylalanine ammonia lyase (PAL) and chalcone isomerase (CHI), keep the quality of the fruit storage, change color and soften normally when fruits storage to the stage of complete ripeness. 2.0g/L treatment had the most significant preservation effect. But the higher concentration of GA3 treatment (3.0g/L and 4.0g/L) of the fruit storage to maturity when the fresh can mature softening normally, but the peel can not completely turn color,had a "stagnant green" phenomenon,which to some extent affected the ’Guifei’ mango appearance quality, reduce its commodity value. In addition, post-harvest GA3 treatment had a significant effect on the content of endogenous GA3, and the content of endogenous GA3 increased with the increase of GA3 concentration.(2) In the different stages of fruit development (flowering period, young fruit period,fruit enlargement period), the effect of different GA3 concentrations (0, 0.3, 0.5,1.0, 2.0,3.0g/L) on the storage quality and pre-harvest physiology were studied by using the 10-years-old ’Tainong No.1’ mango trees as the experimental material. The results showed that, compared with CK, pre-harvest GA3 treatment could delay the change of TSS content,decrease the loss of Vc, keep the hardness and TA content, inhibit the degradation of chlorophyll and carotenoid and anthocyanin accumulation, decreased Chlase, PAL, CHI activity, delayed maturation and senescence, with 2.0g/L treatment had the best fresh-keeping effect, 1.Og/L treatment followed and 3.0g/L treatment had the worst fresh-keeping effect.(3) The effects of pre-harvest GA3 treatment on the change of related enzyme activity of color change in ’Guifei’ mango and ’ Tainong No.1’ mango were studied. The results showed that the activity of Chlase, PAL and CHI showed the trend of peak shape after rising and decreasing during the storage time. Pre-harvest GA3 treatment could reduce the activity of Chlase, PAL and CHI and delayed the peak of enzyme activity effectively.Among them, the most significant inhibitory effect of ’Guifei’ mango was 4.0g/L, the most significant inhibitory effect of ’Tainong’ mango was 2.0g/L.(4) In order to explore the molecular mechanism of the high concentration with GA3 which caused ’Guifei’ mango peel incomplete change in peel color until ripening. The’Guifei’ mango peel were used as the material, which were treated with spraying different concentrations of GA3 during the different stages of development, and the key enzymes in the carotenoid synthesis: (phytoene synthase, PSY), key enzymes in the anthocyanin synthetic (Chalcone synthas,CHS) and chalcone isomerase (CHI) gene expression levels were analyzed. The results showed that, compared with CK, the expression level of PSY,CHS,CHI genes was significantly inhibited by pre-harvest GA3 treatment. Among them,the most significant inhibitory effect of was 4.0g/L. At the middle of storage (18th day),compared with CK, the relative expression of PSY, CHS and CHI genes of 4.0g/L were respectively lower than 21.705, 4.191, 1.751. It is suggested that higher concentration of GA3 pre-harvest treatment caused post-harvest ’Guifei’ mango had a "stagnant green"phenomenon in the ripe period, it is closely related to the inhibition in expression of PSY,CHS and CHI gene. |
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