| Tea plant [Camellia sinensis(L.)O.Kuntze] is an important leaf-based woody economic crop.At present,the global warming situation is getting more and more serious,especially in summer,extreme high temperature weather occurs frequently,which seriously affects the growth and metabolism of tea plants.In addition,the yield and quality of tea are also greatly reduced.There are many studies on the effects of exogenous substances related to plant stress resistance,for example,γ-aminobutyric acid(GABA)plays an important role in plant resistance to stresses such as salt and drought.However,as an amino acid growth regulator,GABA has not been reported in the study of heat resistance of tea plants.In this paper,’Zhongcha 108’ was used as the test material and four treatment groups were set up,namely,control group—CK(25℃/20℃);high temperature group—H(42℃/40℃);high temperature and exogenous spraying GABA group—H + G(42℃/40℃+ 5 m M GABA);high temperature and exogenous spraying 3-MPA group—H + M(42℃/40℃ + 0.1 m M 3-MPA),and sampled at 0,4,8,and 24 h after treatment,respectively.The research contents and conclusions are as follows:1、By detecting the content of endogenous GABA in different treatment groups under each sampling time point,it was found that heat stress could rapidly stimulate the accumulation of endogenous GABA in tea leaves in a short period of time;moreover,exogenous GABA could further promote the accumulation of endogenous GABA content in tea leaves under heat-stress condition.2、The effects of exogenous GABA on tea physiology under heat stress were studied by detecting the indexes of four key physiological systems in plants.Cell membrane system:GABA could inhibit the increase of MDA content and electrical conductivity in tea leaves under heat stress to a certain extent.Osmotic regulation system: GABA could promote the accumulation of soluble sugar and free proline in tea leaves under heat stress to some extent,but it was found that soluble sugar began to accumulate in the early stage,while proline had obvious accumulation at the later 24 h.Antioxidant defense system: exogenous GABA could promote the increase of SOD,POD,CAT and APX activities in tea leaves under heat stress to a certain extent.Photosynthetic system,stomatal aperture and chlorophyll: GABA could promote the increase of Pn,Cond,Tr and chlorophyll content in tea leaves under heat stress to a certain extent.In addition,GABA could also promote the increase of stomatal aperture at the initial 4 h of heat stress,while Ci was reduced.3、The effects of exogenous GABA on tea leaves quality under heat stress were investigated by measuring the contents of the three major quality components in tea leaves,as well as the activities of enzymes related to flavonoid synthesis and the quantitative expression of related genes.The results showed that phenols: GABA promoted the accumulation of tea polyphenols,catechins and most catechin monomers in tea leaves under heat stress.Among them,exogenous GABA could enhance the expression levels of flavonoid metabolism-related genes(except CHS,LAR and ANR)and the activities of related enzymes in tea leaves under heat stress to some extent,and then promoted the accumulation of phenolics in tea leaves.In addition,GABA showed a significant positive correlation with the content of tea polyphenols(r = 0.649),especially with total catechins(r= 0.837)and with EGC content(r = 0.896),but no significant correlation with ECG + CG,EC and C.Amino acids: GABA could promote the increase of total free amino acids in tea leaves under heat stress to a certain extent,especially in the treatment of 24 h,among which the promotion effect was more obvious for Thea,Asp and Ser in each component of amino acids.Caffeine: GABA did not significantly promote or inhibit caffeine content in tea leaves heat-stress condition.4、The effects of exogenous GABA on the expression levels of CsHSPs genes in tea leaves under heat stress were investigated by measuring the quantitative expression of several CsHSPs genes(including CsHSP90.1,CsHSP90.7,CsHSP70.1,CsHSP70.17,CsHSP6,CsHSP10 and CsHSP22).It was found that GABA could up-regulate the expression levels of CsHSP90.1,CsHSP90.7 and CsHSP22 genes under heat stress to a certain extent,especially for CsHSP90.7,and down-regulate the expression levels of CsHSP70.1,CsHSP6 and CsHSP10 genes in tea leaves under heat stress,especially for CsHSP6.In addition,it was inferred that the response of tea plants to heat stress may be regulated by the interaction of multiple CsHSPs genes or other genes in the signaling pathway,and GABA was involved in the regulation of CsHSPs gene expression level. |
