Abstract
The fine-tuned regulation of the Halliwell-Asada cycle (ascorbate-glutathione pathway) in Arabidopsis thaliana under boron (B) toxicity was shown in our previous report. In this study, we investigated the expression levels of some members of the glutathione S-transferase (GST) superfamily, such as phi (GSTF2, GSTF6, GSTF7, and GSTF8), tau (GSTU19), and zeta (GSTZ1) classes in Arabidopsis thaliana that were exposed to 1 mM boric acid (1B) and 3 mM boric acid (3B). Additionally, the expression levels of genes for glutathione (GSH) and phytochelatin biosynthesis as well as miR169 and miR156 were evaluated in Arabidopsis thaliana exposed to 1B and 3B. Moreover, changes in the levels of total GST activity; GSH; and total, protein-bound, and nonprotein thiols were spectrophotometrically determined. GSH levels and nonprotein thiol content did not change significantly following both B-toxicity conditions. Expression levels of GSH1 and GSH2 stayed stable under 1B toxicity; however, GSH1 expression increased significantly under 3B conditions in Arabidopsis thaliana. The expression levels of four genes from phi class members of GST were not dramatically changed under B-toxicity conditions. However, the transcript levels of miR169, ATGSTU19, and ATGSTZ1 were significantly increased after 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 our knowledge, this is the first report displaying an integrative view of high-B-induced regulation of GSH-dependent enzymatic machinery at different biological organization levels in Arabidopsis thaliana.
Highlights
Boron (B) is an essential micronutrient for plants (Warington, 1923), high levels of B are a crucial problem for crops, mainly in arid areas in the world (Landi et al, 2012)
Responses of GSH metabolism to B toxicity at a biochemical level Treatment 1 mM boric acid (1B) did not cause any significant change in total thiol content in Arabidopsis thaliana (Table 2)
In our previous report, we have shown that oxidative damage is not provoked by higher B toxicity as phenolics and proline are promoted, superoxide dismutase (SOD) is strongly stimulated, and the components of the AsA–GSH cycle are coordinately regulated at the transcriptional level (Kayıhan et al, 2016)
Summary
Boron (B) is an essential micronutrient for plants (Warington, 1923), high levels of B are a crucial problem for crops, mainly in arid areas in the world (Landi et al, 2012). Increased levels of flavonoid and anthocyanin in tomato (Cervilla et al, 2012); higher phenolic content in sweet basil (Pardossi et al, 2015); significant increases in catalase activity (CAT; EC 1.11.1.6), superoxide dismutase (SOD; EC 1.15.1.1), and ascorbate peroxidase (APX; EC 1.11.1.11) in chickpea (Ardıc et al, 2009) and soybean (Hamurcu et al, 2013) were determined under toxic B conditions. By means of thiol metabolism, sulfur uptake and its assimilation culminate in cysteine synthesis. This metabolism and the AsA–GSH cycle play a critical role in metal toxicity tolerance by accumulating compatible organic compounds and scavenging reactive oxygen species (ROS) in plants (Singh et al, 2015)
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