Study Of Lignin Metabolism In Lycium Ruthenicum Murr. Under Salt Stress

Salinization is one of the main environmental problems faced by global agricultural and natural ecosystem. Studying the adjustment mechanisms of halophytes would not only provide theoretical basis for improving the salt resistance of non-halophytes, but also have important implications for the improvement and utilization of salinized land. Phenylpropanoid pathway is an effective approach to the synthesis of plant secondary metabolites. Its subordinate pathways mainly include lignin synthesis pathway and flavonoids synthesis pathway. Lignin is a kind of complex high molecular compound that exists in most land plants. Its content and enzymes activity are closely related to the growth, disease resistance and stress resistance of plants. Until present day, the metabolic and regulatory mechanisms of lignin under salt stress have rarely been understood. Based on the results of the iTRAQ analysis of the salt-treated (NaCl)callus of Lycium ruthenicum Murr., this study focuses on the change of lignin content in the callus treated under different salinity and at different time. Combined with the activity determination of phenylalanine ammonialyase (PAL) and peroxidase (POD), this is also a preliminary study on the response mechanism of Lycium ruthenicum Murr. under salt stress on phenylpropanoid metabolic pathway. Major results of the study are as follows:1. Under different treatment, the lignin content of Lycium ruthenicum Murr. changes from15.82±0.06%to7.51±0.14%. The maximum value is achieved under100mM salt treatment for2h; the minimum value is achieved under200mM salt treatment for480h.2. The lignin content in the callus of Lycium ruthenicum Murr. shows a downward trend under salt stress. Under the same concentration of salt treatment, with the extension of salt processing time, the lignin content shows a clearer downward trend. For the same processing time, the lignin content decreases along with the increase of salt concentration; this trend becomes clearer with longer processing time. Under control conditions, the lignin content is basically stable, with no obvious accumulation effect.3. Under salt stress, the PAL activity of lycium ruthenicum Murr. shows an upward trend and there are obvious differences between every two treatments except between the100mM treatment and the control condition. Studies in the lab show that under salt stress the content of flavonoids in lycium ruthenicum Murr. increases significantly. This indicates that under salt stress, phenylpropanoid metabolism of Lycium ruthenicum Murr. is generally rising and lignin reduction is due to the selective expression of phenylanine metabolic pathway. POD enzyme activity shows an upward trend and there are extremely obvious differences between every two treatments. Results of the iTRAQ analysis show that the variety of POD, the expression of which increases under salt stress, has no relation to lignification.4. ITRAQ analysis show that under salt stress, among branches of the lignin metabolic pathways of Lycium ruthenicum Murr., only the expression of C3H declines. As the expression decline of C3H would lower the lignin content, it is inferred that the decrease of the lignin content of Lycium ruthenicum Murr. is caused by the decline of C3H.The above results show that the lignin content of Lycium ruthenicum Murr. decreases under salt stress; on the Phenylpropanoid metabolic pathway, the response of Lycium ruthenicum Murr. to salt stress is, through selective expression, to reduce the synthesis of lignin and increase the accumulation of flavonoids; this process is achieved through the decline of C3H expression.