| Due to extensive area of distribution and improvement difficulty, acidic soil has become the limiting factor in the development of agricultural production. Al toxicity is one of the major factors limiting crop production on acidic soil. Therefore, to reduce or eliminate Al toxicity in acidic soil is an important problem to be solved urgently for the world’s agricultural production. Salicylic acid (SA) as a new type of plant hormones and signaling molecules was involved in plant growth and development in a wide range of various processes, and mediated responses for biological and abiotic stresses in plants. In recent years, there was more and more researches on SA in resistance, but the research on SA relieving Al stress in plant was less. Chlorogenic acid (CGA) has strong antioxidant activity, and is the protective agent for IAA. It may be associated with plant growth and stress response. In this study, a method of solution culture to Al-sensitive black soybean (SB) was used to study the effects of exogenous SA and CGA on the physiological parameters and Al stress-related gene expression in SB root under Al stress. The aim of this study is to explore the molecular mechanisms of exogenous SA and CGA alleviating Al toxicity in SB. The main findings are as follows:Low concentrations (10 and 20μmol·L-1) of SA alleviated inhibition of root elongation caused by Al toxicity, wherein the alleviation effect of 20μmol·L-1 SA was more significant. However, higher concentration (40 and 60 μmol·L-1) of SA and SA synthesis inhibitors paclobutrazol (PAC) increased inhibition of root elongation caused by Al toxicity. Exogenous 20 μmol·L-1 SA decreased the content of Al, MDA and H2O2 and changed antioxidant enzyme activity in SB root under Al stress. And the citric acid amount exudated by root was about 1.6 times as higher as that of single Al treatment. Expression analysis showed that exogenous 20 μmol·L-1 SA enhanced the expression of the 12 substype of 14-3-3 isoforms, plasma membrane H+-ATPase (GHA2) and multidrug and toxic compound extrusion transporter (MATE) gene in SB under Al stress. The results of the co-immunoprecipitation showed that exogenous 20 μmol·L-1 SA improved the levels of protein phosphorylation for plasma membrane H+-ATPase and its binding capacity with 14-3-3 protein under Al stress. The results of the activity of plasma membrane H+-ATPase and H+ pump showed that exogenous 20 μmol·L-1 SA enhanced the activity of plasma membrane H+-ATPase and H+ pump under Al. The effect of exogenous PAC treatment was opposite with those of SA. It was suggested that exogenous SA may enhance the SB tolerance to Al stress by inducing MATE expression and enhancing 14-3-3 and plasma membrane H+-ATPase protein levels and interaction between them to increase citric acid exudation.Low concentrations (0.004 and 0.01 g·L-1) of CGA alleviated inhibition of root elongation caused by Al toxicity, and promoted the increasement of lateral roots number under Al stress, wherein the alleviation effect of 0.01 g·L-1 CGA was more significant. However, for higher concentration (0.02 and 0.04 g·L-1) of CGA, the effect of alleviating inhibition of root elongation caused by Al toxicity reduced, and the effect of promoting lateral roots numbers also declined. Exogenous 0.01 g·L-1 CGA decreased the Al and MDA content, increased H2O2 content and changed antioxidant enzyme activity in SB root under Al stress. And the citric acid content in root exudates was about 2 times as higher as that of single Al treatment. Expression analysis showed that exogenous 0.01 g·L-1 CGA enhanced the expression of the 3 substype of 14-3-3 isoforms and plasma membrane H-ATPase (GHAT) gene, and inhibited the gene expression of MATE in SB under Al stress. The results of the co-immunoprecipitation showed that exogenous 0.01 g·L-1 CGA improved the levels of protein phosphorylation for plasma membrane H+-ATPase and its binding capacity with 14-3-3 protein under Al stress. The results of the activity of plasma membrane H+-ATPase and H+ pump showed that exogenous 0.01 g·L-1 CGA enhanced the activity of plasma membrane H+-ATPase and H+ pump under Al stress. It was suggested that exogenous SA may enhance the SB tolerance to Al stress by enhancing 14-3-3 and plasma membrane H+-ATPase protein levels and interaction between them to increase citric acid exudation. |
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