Effects Of γ-aminobutyric Acid On Growth And Physiological Metabolism Of Vaccinium Plantlets In Vitro

The Vaccinium（Vaccinium cprymbosum L.）is a small berry fruit tree of the genus Vaccinium in the Rhododendron family.The Vaccinium fruit has high nutritional value and health functions,and the market demand has been expanding in recent years,and the demand for high-quality plantlets has also increased.Tissue culture technology is the main method for commercial seedling breeding of Vaccinium.However,the growth of Vaccinium plantlets is slow,the breeding cycle is long and the reproduction efficiency is low.In addition,due to the prolonged culture time,the nutrients in the culture medium continue to decrease,and toxic and harmful substances continue to accumulate,resulting in the growth of Vaccinium plantlets weak or browning and vitrification,which seriously reduces the quality of the plantlets.Therefore,accelerating the growth of plantlets in vitro,improving the quality of in plantlets in vitro and shortening the breeding cycle have become important issues to be solved for plantlets in vitro breeding of Vaccinium.γ-aminobutyric acid（GABA）,a four-carbon non-protein amino acid,can improve plant resistance to a variety of adversities and promote plant growth,and has become a hot research topic in the field of plant adversity,but its application effect and mechanism in tissue culture are still unclear.In this study,we used Vaccinium plantlets in vitro as experimental materials to analyze the effect of GABA addition in culture medium on the growth and differentiation and physiological metabolism of plantlets in vitro,and also combined with histological methods to analyze the mechanism of GABA affecting the growth and development of Vaccinium plantlets in vitro,the results of the study are as follows.1.Exogenous addition of GABA can promote plant growth and metabolism by regulating the water content of Vaccinium plantlets,and increase the fresh weight,dry weight,and plant height of seedlings,so we concluded that exogenous addition of GABA can promote the growth of Vaccinium plantlets,and 0.5 g·L^-1 treatment is the most effective in terms of comprehensive effect and cost.It was also found that 0.5 g·L^-1 GABA had the best effect on the growth of‘Primadonna’,‘Rubel’,‘Northblue’,‘Nanda’and‘O’Neal’,‘O’Neal’and‘Northblue’all had some promotion effect on the growth of Vaccinium plantlets,but the effect was different for each variety.2.Exogenous addition of 0.5g·L^-1 GABA significantly increased the stomatal opening,water content,free/bound water and osmoregulatory substance content of Vaccinium plantlets,promoted the gas exchange and water metabolism of test tube seedlings under histoponic conditions,and promoted the growth of plantlets in vitro;maintained the osmotic balance of plantlets in vitro,and improved the adaptability of plantlets in vitro to the histoponic environment at the later stage of histoponic cultivation.3.Exogenous addition of 0.5g·L^-1 GABA significantly increased the content of endogenous growth hormone（IAA）and cytokinin（i PA）and decreased the content of growth inhibitory hormones gibberellin（GA3）,abscisic acid（ABA）and methyl jasmonate（JA-me）in Vaccinium plantlets in vitro,and regulated the hormone balance to promote the growth of Vaccinium plantlets in vitro.4.Exogenous addition of 0.5g·L^-1 GABA significantly increased the content of antioxidant substances（GSH,As A）and activities of antioxidant enzymes（POD,SOD,GR,APX）in Vaccinium plantlets in vitro,reduced the production of ROS,alleviated oxidative stress in test-tube seedlings under unfavorable environment,alleviated membrane lipid peroxidation,and reduced the browning rate of Vaccinium plantlets in vitro.5.Combined with the results of transcriptome and metabolome analysis,we concluded that exogenous addition of 0.5g·L^-1 GABA could promote sucrose degradation,TCA cycle,sugar xenobiotic process and carbon and nitrogen flow,provide energy and substrate for starch and cellulose synthesis,and promote the growth and dry matter accumulation of plantlets.Meanwhile,exogenous GABA significantly increased the content of flavonoids,steroids,terpenoids and other secondary metabolites involved in plant communication defense in Vaccinium plantlets,thus improving plant adaptability to unfavorable growth conditions.