Recovery Effect And Mechanism Of γ-aminobutyric Acid On Hyperhydric Plantlets Of Blueberry In Vitro

Hyperhydricity is a physiological disease change in the process of plant tissue culture.The hyperhydric plantlets have abnormal morphology and anatomical structure,physiological metabolism disorder,proliferation,differentiation and rooting difficulties,low survival rate of transplanting,and difficult to return to normal,which has caused huge economic losses and human waste to the commercial production of test-tube seedlings.γ-Aminobutyric acid（GABA）is a four-carbon non-protein amino acid,which plays an important role in promoting plant growth and development and improving plant stress resistance.Using hyperhydric plantlets of different varieties of blueberry as materials,the effects of adding GABA in the culture medium on the recovery and growth,proliferation and differentiation,physiological metabolism and anatomical structure of hyperhydric shoots were explored.The main results were as follows:1.Adding GABA of appropriate concentration(0.5～0.7 g·L^-1)GABA in the medium can improve the recovery rate,chlorophyll content,plant height,proliferation and fresh weight of‘O′Neal’hyperhydric plantlets.Among them,0.5 g·L^-1 has the best effect.This concentration can also promote the growth and differentiation of many blueberry varieties such as‘Nanhao’after hyperhydricity recovery.2.0.5 g·L^-1 GABA could significantly increase the contents of soluble sugar,ascorbic acid（ASA）and reduced glutathione（GSH）,and the activities of superoxide dismutase（SOD）,catalase（CAT）and glutathione reductase（GR）;significantly decrease the production rate of superoxide radical（O₂.^-）and the content of malondialdehyde（MDA）in‘O′Neal’and‘Nanhao’plantlets.3.0.5 g·L^-1 GABA could significantly increase the contents of auxin（IAA）and isopentenyl adenine（i PA）,significantly reduce the content of methyl jasmonate（JA-me）,and significantly improve the ratio of growth-promoting hormones（IAA,i PA,BR,GA₃）to inhibitory hormones（ABA,JA-me）.4.Compared with hyperhydric plantlets cultured without GABA,epidermal cells and palisade tissue cells of plantlets cultured with 0.5 g·L^-1 GABA were more closely and neatly arranged;cytoplasmic density enlarged,the number of mitochondria increased,and the lamellar structure of thylakoid were more neat and clear.The above results show that 0.5 g·L^-1 GABA added to the medium can,on the one hand,alleviate the damage caused by hyperhydricity to plantlets,protect cell structure,maintain normal cell physiological metabolism and promote the growth of hyperhydric plantlets to return to normal by improving osmotic regulation ability and anti-oxidation ability.On the other hand,it can promote cell growth and division by increasing the content and ratio of endogenous auxin and cytokinin in plantlets,which in turn can promote the growth of test-tube plantlets after recovery.This study provides an effective method for the prevention and control of hyperhydricity of test-tube plantlets,and also provides a basis for the extensive application of GABA in plant tissue culture.