Effects Of γ-aminobutyric Acid On Growth And Photosynthetic Characteristic Of Amaranth Under Low Temperature Stress

Amaranthus tricolor L.is an annual C4 herb of the family Amaranthaceae,with rapid growth and high yield.It is a common green leafy vegetable in summer.It is rich in betalain and can be used as an important source of betalain extraction.Temperature is an important environmental factor for plant growth and secondary metabolism.Low temperature can reduce the chlorophyll content and chlorophyll fluorescence parameters of plants,and inhibit the growth of amaranth and the betalain synthesis.Exogenous GABA can reduce the accumulation of harmful substances in plants.It can help maintain cell morphology,improve cell function under stress,reduce the damage of stress to the photosynthetic system,and improve photosynthesis and chlorophyll fluorescence parameters.In this study,‘Suxian No.1’ was used as the experimental material to explore the effects of low temperature stress and exogenous GABA on the growth and nutritional quality of amaranth.The expression trend of related genes of photosynthesis and glutamate decarboxylase(GAD)were investigated.Finally,the AtrNADP-ME was transferred into Arabidopsis thaliana to further verify its function.The main results are as follows:1.Effects of low temperature stress on the growth and nutritional quality of amaranthThe three-leaf stage amaranth was treated with different low temperature,and five indexes including plant height,chlorophyll content,chlorophyll fluorescence parameter,betalain content and endogenous GABA content were analyzed at different temperatures.The results showed that the plant height of amaranth showed a downward trend with the decrease of temperature.The growth of amaranth was slow at 15 ℃and stopped at 10 ℃,indicating that low temperature significantly inhibited the growth of amaranth,and the longer the low temperature stress,the more obvious the degree of inhibition.The contents of chlorophyll and betalain also decreased significantly with the decrease of temperature,and the contents also decreased with the prolongation of treatment time;chlorophyll fluorescence parameters were significantly inhibited at 10 ℃;low temperature can promote endogenous GABA content accumulation.Therefore,low temperature stress inhibited the growth of amaranth,decreased the contents of chlorophyll and betalain,and decreased the fluorescence parameters of chlorophyll,which promoted the accumulation of endogenous GABA content.2.Effects of exogenous GABA on growth and nutritional quality of amaranth under low temperature stressAfter spraying different concentrations of GABA,amaranth at the3-leaf stage was cultured at 15 ℃,and the five indexes of amaranth plant height,chlorophyll content,chlorophyll fluorescence parameters,betalain content and endogenous GABA content were analyzed.With the increase of exogenous GABA concentration,the plant height of amaranth first increased and then decreased.Compared with spraying water as the control,the exogenous GABA concentration of 100 mg/L treated amaranth plants was the highest,while the concentration of 200 mg/L inhibited plant growth;chlorophyll content increased with the increase of exogenous GABA concentration.However,there was no significant difference in chlorophyll fluorescence parameters;the content of betalain was the highest under the treatment of 50 mg/L GABA;the content of endogenous GABA was the highest when the exogenous GABA was 100mg/L.Therefore,low concentration of exogenous GABA can promote the growth of amaranth,relieve the degradation of amaranth chlorophyll at low temperature,and promote the synthesis of amaranth betalain.Exogenous GABA also has a certain promoting effect on the synthesis of endogenous GABA.3.Effects of low temperature stress and exogenous GABA on the expression of photosynthesis genes and GAD genes in amaranthqPCR analysis showed that the expression of AtrPEPC increased first and then decreased with the decrease of temperature,while AtrPPCK,AtrMDH,AtrNADP-MDH,AtrNAD-ME,AtrNADP-ME,and AtrPPDK responded to the decrease of temperature by down-regulating the expression as a whole,and photosynthesis decreased.The gene expression level was positively correlated with temperature as a whole.The expression of AtrGAD gene showed a significant upward trend with the decrease of temperature,and low temperature induced the expression of AtrGAD gene.After 3 days of treatment,exogenous GABA inhibited the expression of AtrGAD gene in amaranth;when treated for 6 days and12 days,exogenous GABA instead promoted the expression of AtrGAD gene in amaranth.The effect of exogenous GABA on the expression of AtrNADP-ME gene in amaranth was not obvious in a short period of time.With the extension of time,exogenous GABA promoted the expression of AtrNADP-ME gene in amaranth.Therefore,low temperature stress inhibited the expression of photosynthesis genes and promoted the expression of AtrGAD gene;exogenous GABA could promote the expression of AtrGAD and AtrNADP-ME genes in amaranth under low temperature stress.4.Functional analysis of amaranth AtrNADP-METhe function of amaranth AtrNADP-ME was verified by the method of transforming Arabidopsis with Agrobacterium.PCR amplification of transformed plants and wild-type Arabidopsis showed that the target band was not amplified in wild-type,while AtrNADP-ME,GUS and Hyg genes were simultaneously amplified in transformed plants.The results of qPCR showed that the expression of AtrNADP-ME gene in transformed plants was more than 2000 times that of wild type,and its function needs to be further verified.