Regulation of boron toxicity responses via glutathione-dependent detoxification pathways at biochemical and molecular levels in Arabidopsis thaliana

Abstract

The fine-tuned regulation of the Halliwell–Asada cycle (ascorbate–glutathione pathway) in Arabidopsis thaliana underboron (B) toxicity was shown in our previous report. In this study, we investigated the expression levels of some members of theglutathione S-transferase (GST) superfamily, such as phi (GSTF2, GSTF6, GSTF7, and GSTF8), tau (GSTU19), and zeta (GSTZ1) classesin Arabidopsis thaliana that were exposed to 1 mM boric acid (1B) and 3 mM boric acid (3B). Additionally, the expression levels ofgenes for glutathione (GSH) and phytochelatin biosynthesis as well as miR169 and miR156 were evaluated in Arabidopsis thalianaexposed to 1B and 3B. Moreover, changes in the levels of total GST activity; GSH; and total, protein-bound, and nonprotein thiols werespectrophotometrically determined. GSH levels and nonprotein thiol content did not change significantly following both B-toxicityconditions. Expression levels of GSH1 and GSH2 stayed stable under 1B toxicity; however, GSH1 expression increased significantlyunder 3B conditions in Arabidopsis thaliana. The expression levels of four genes from phi class members of GST were not dramaticallychanged under B-toxicity conditions. However, the transcript levels of miR169, ATGSTU19, and ATGSTZ1 were significantly increasedafter 1B and 3B exposure. These GST genes may have a role in the dramatic increase of total GST activity under toxic B. To the best of ourknowledge, this is the first report displaying an integrative view of high-B–induced regulation of GSH-dependent enzymatic machineryat different biological organization levels in Arabidopsis thaliana.