Salicylic acid involved in chilling-induced accumulation of calycosin-7-O-β-d-glucoside in Astragalus membranaceus adventitious roots

Calycosin and calycosin-7-O-β-d-glucoside (CG) are major isoflavonoids in Astragalus membranaceus and have multiple beneficial activities. Adventitious roots (ARs) are becoming attractive resources to obtain biologically active compounds. Salicylic acid (SA) is an important endogenous phytohormone, which is involved in the regulation of biotic and abiotic stresses. However, little is known about the potential role of SA on isoflavonoid accumulations under chilling stress. In the present study, calycosin was found to accumulate mostly in its glucosyl conjugate (CG) form in A. membranaceus ARs (AMARs). Compared to control conditions (25 °C), chilling (5 °C) induced the accumulation of CG, which was confirmed by increased expression levels of gene-encoding enzymes in the CG biosynthetic pathway. Furthermore, chilling triggered the accumulation of SA prior to CG accumulation. In addition, the inhibition of SA biosynthesis with paclobutrazol (PAC) in chilling-exposed AMARs suppressed the accumulation of CG and gene expressions, while exogenous addition of SA to PAC-treated AMARs restored CG content and gene expressions. These results indicated that in AMARs, SA involved in chilling-induced CG accumulation by regulating the expression levels of genes in the CG biosynthetic pathway.