Advances in grape coloration regulated by plant growth regulators

Abstract: Fruit color is an important indicator of the quality of grape berry, which directly affects the nutritional and commodity value of grapes. Fruit coloration is determined by pigments, such as chlorophyll, carotenoids and anthocyanidins. The main pigment in the colored grape is anthocyanidin, which is present in the form of anthocyanins in grapes. Synthesis of anthocyanins is regulated by internal factors such as genotype, enzymes, hormones, and external factors such as light, temperature, water, soil nutrient and so on resulting in poorly colored fruit, thus affecting quality and commodity value. Therefore, it is necessary to take measures to promote coloration of grape. Using of plant growth regulators is undoubtedly a convenient and quick means. In this paper, the effects and mechanisms of different plant growth regulating substances on grape coloration were expounded from the physiological and molecular levels, including abscisic acid (ABA) , naphthalene acetic acid (NAA) , ethephon (ETH) , jasmonates (JAs) , gibberellic acid (GA) and brassinolides (BRs) . On physiological level: 1. Promoting coloring by increasing sugar content. Coloration of the fruit depends on anthocyanin content. Sugar is an important base material for anthocyanins synthesis. ABA, JAs, BR, etc. can increase the accumulation of sugar in fruits, thereby promoting the formation of anthocyanins. However, NAA reduces the sugar content of the fruit, which is not conducive to anthocyanin synthesis. 2. Promoting coloring by affecting the pigment content of fruits. The use of exogenous plant growth regulators (ABA, ETH, JAs, GA, BRs) can induce chlorophyll degradation, promote the synthesis of carotenoids and anthocyanins, accelerate the color change of the peel and the maturation process, but NAA has the opposite effect. 3. Promoting coloration by regulating endogenous hormones. Plant growth regulating substances can regulate the content of endogenous hormones and the balance between them, moreover, regulates fruit maturation by interaction of hormones. For example, exogenous ABA increases the content of endogenous ABA and ethylene, while reduces the content of indoleacetic acid (IAA) , GA, and Zealin-riboside (ZR) ; Exogenous ETH treatment can increase endogenous ETH content in fruit and then promoting coloring; BRs can increase the content of endogenous ABA, promote the release of ETH, reduce the content of IAA in the early stage of grape ripening, so that they can promote the coloration and maturation of grapes. On molecular level: The biosynthesis of anthocyanins is controlled by the expression level of structural genes and transcription factors. Structural genes directly encode biosynthesis enzymes in anthocyanin biosynthesis pathway, including: chalcone synthases (CHS) , chalcone isomerase (CHI) , flavonoid 3-hydroxylase (F3 H) , flavonoid 3 '-hydroxylase (F3'H) , flavonoid 3', 5'-hydroxylase (F3'5'H) , dihydroflavonol4-reductase (DFR) , leucoanthocyanidin dioxygenase (LDOX) and UDP glucose-flavonoid 3-O-glucosyltranferase (UFGT) . Transcription factors are not directly involved in the formation of anthocyanins, however they can regulate the expression and pattern of anthocyanin biosynthesis genes while controlling the changes in anthocyanins in time and space. At present, three kinds of anthocyanin-synthesized transcription factors have been isolated and identified: R2 R3-MYB protein, b HLH protein and WD40 protein. Plant growth regulators (ABA, ETH, JAs, BRs, etc) can regulate the coloration of grape fruit through increasing the expression of anthocyanin related structural gene and transcription factors. NAA down-regulates the expression of structural genes, inhibits the synthesis of anthocyanins and delays fruit ripening. Currently plant growth regulating substances are widely used in grape coloring, but there are still many problems such as the abuse of plant growth regulators by people eager to promote coloring using excessive concentrations, resulting in poor coloration, fruit detachment, fruit cracking, leaf browning and other side effects. In view of the above problems in practical application, the variety characteristics of grape, the scientific cultivation management measures and the mechanism of plant growth regulation substances should be combined to select suitable application concentration, period and method for achieving a comprehensive quality of fruit control and improvement.