梨果实糖酸研究进展

Research progress in sugar and acid in pear fruit

可溶性糖酸含量是影响梨果品质的经济性状,是人类长期驯化选择的重要性状。在梨果实生长发育、成熟与衰老过程中,糖酸代谢发生一系列生理生化反应,果实中的糖酸含量以及组分变化存在一些规律性。梨果肉主要可溶性糖包括蔗糖、果糖、葡萄糖、山梨醇等,主要可溶性酸包括苹果酸、柠檬酸等,糖酸含量及组分和糖酸比显著影响果实风味。影响梨果肉糖酸含量及组分的因素主要包括品种、光照、激素、肥料、采后技术及砧木等。果实糖酸代谢是十分复杂的生理生化代谢网络的一部分,糖酸是一个由多个基因控制的数量性状,许多关键的功能基因已被验证。目前梨果糖酸研究已在相关酶、糖转运体、转录因子、QTLs分子标记、基因组学、蛋白组学等方面取得重要的研究进展。围绕上述研究,综述了糖酸的主要研究进展,并进行总结和展望,以期为梨果糖酸含量及组分评价、功能基因挖掘和指导梨育种提供参考。

Pears are the third temperate fruit crop in the world and are widely popular due to their unique taste.The contents of soluble sugars and organic acids in pear fruits are very important to fruit quality.The differences in the content and composition of soluble sugars and organic acids in the fruit contribute to the different flavors of different pear varieties.During the growth,development,matura-tion and aging of pear fruits,a series of physiological and biochemical reactions occur through sugar and acid metabolism,and there are some patterns in the sugar and acid content and component changes in the fruit.Research on the contents of soluble sugars and organic acids in pear fruits has emerged end-lessly,and a significant progress has been made.This article will provide an overview of the research on the sugar and acid contents in pear fruits.It mainly consists of four aspects:research progress in sug-ar and acid contents during fruit growth and development,sugar and acid content in post harvest pear fruits,factors affecting sugar and acid content and molecular mechanisms of sugar and acid change.During fruit growth and development,organic acids are formed in the early stages of fruit development and gradually decrease as the fruits mature.The organic acid components in pear fruits mainly include malic acid,citric acid,quinic acid,oxalic acid,shikimic acid and tartaric acid.Pear varieties are divided into malic acid dominant and citric acid dominant varieties based on the content of each organic acid component in the fruit.With Asian pear varieties,the main organic acid found in most pear varieties is malic acid,while with European pear varieties,the main organic acid found in most pear varieties is cit-ric acid.Malic acid shows a first increasing and then decreasing trend throughout the entire growth and development process,while citric acid dominant varieties will undergo a transition of malic acid de-creasing and citric acid increasing in the middle stage of fruit development.Malic acid is the main fac-tor causing significant differences between varieties.The total soluble sugar content is relatively low in the early stage of fruit development and gradually increases with fruit maturity.The soluble sugar com-ponents present in pear fruits mainly include sorbitol,fructose,glucose and sucrose.Most pear varieties have sorbitol as the main sugar in the young fruit,while fructose is the main sugar in the mature fruit.There are significant differences in the proportion of sugar components at different developmental stag-es,with an increase in fructose content and a significant decrease in sorbitol content during maturity.Su-crose is an important factor causing differences among varieties.Pears belong to the respiratory climac-teric type of fruit.During storage,fructose and glucose contents in the fruit gradually increase,sorbitol and malic acid contents gradually decrease,and sucrose first increase and then decrease.Under low tem-perature storage conditions,the contents of fructose,glucose and sucrose increase until they gradually decrease after 90 days.The organic acid contents show a trend of first decreasing and then stabilizing.Although the total soluble sugar content of refrigerated fruits is higher than that of unfrozen fruits,long-term refrigeration can lead to a deterioration and decrease in sucrose content in the fruits.Bagging treat-ment could reduce the content of total soluble sugar and reduce the content of malic acid.The applica-tion of different plant hormones or growth regulators could affect the sugar and acid contents in pear fruits.Ethylene treatment could increase the soluble sugar content and reduce the titratable acid content.GA treatment could increase the contents of sucrose and malic acid.IAA and ABA treatment could pro-mote the accumulation of sorbitol,while MT treatment could increase the content of sucrose and sorbi-tol.Applying potassium and calcium fertilizers could increase the accumulation of glucose,fructose,sorbitol and sucrose in fruits.1-MCP treatment could delay and inhibit the downward trend of organic acids,but also delay the increase of total soluble sugar content.The sugar and acid contents in pear fruits are a quantitative trait controlled by multiple genes.With the rapid development of genomics,many key gene functions has been verified.PbCPK28 promotes the phosphorylation of PbTST4 and Pb-VHA-A1,promoting sugar transport and storage in vacuoles.PbrAc-Inv1 and PbrII5 are involved in the degradation of sucrose.Overexpression of PbPH5 can significantly increase the malic acid content.The sugar transporter family genes involved in sugar transport in pear fruits include PbSWEETs,PbSOTs,PbTMTs,PbSUTs,PbPLTs and PbTSTs.Overexpression of PuSWEET15 increases sucrose content,while silencing PuSWEET15 reduces sucrose content.PbTMT4 is an important contributor to the accu-mulation of fructose,glucose and sucrose in pear fruits.By developing sugar related QTL markers,two individual sugar content regions associated with acid invertase genes have been identified in linkage groups LG1 and LG7.This article has mainly summarized and reviewed the research papers related to the sugar and acid contents of pear fruit in recent years around these four parts,in order to provide refer-ence for the study on sugar and acid contents in the pear fruit,component evaluation,functional gene mining and new variety breeding,and to propose prospects for future research directions.