Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/25/1998
Publication Date: N/A
Citation: Interpretive Summary: Crop plants that can tolerate environmental stress will be able to maintain high yields under stress conditions. Plant cell proteins called glutathione S-transferases (GSTs) are believed to play an important role in protecting plants from various environmental stresses such as plant diseases and pesticides. GSTs attach potentially harmful compounds to glutathione, a naturally occurring compound found in plants. Attaching glutathione to these compounds detoxifies them and prevents plant damage. Lipid hydroperoxides are harmful compounds that are generated in plants exposed to various stresses, such as drought and pathogen invasion. We purified two GST proteins from sorghum and examined their ability to detoxify lipid hydroperoxides. We found that both GST proteins were able to detoxify these compounds, but one protein was more effective than the other. We also found that the two GSTs are glycoproteins which means that their outer rsurfaces are coated with sugar molecules. The sugars may serve to stabilize these proteins and allow them to function under stress conditions. The results of this study indicate that GST proteins may play an important role in protecting plants from toxic lipid hydroperoxides that are formed under stress conditions. This knowledge can be used to develop crop varieties that maintain high yields when growing under conditions of environmental stress.
Technical Abstract: Two glutathione S-transferase (GST, EC 126.96.36.199) isozymes, the homodimeric GST A, and the heterodimeric GST B (B1 and B2 subunits), previously isolated from sorghum were further characterized. Both GST A and GST B exhibited glutathione conjugating activity toward ethacrynic acid and glutathione peroxidase activity toward cumene hydroperoxide, 9-hydroperoxy- -trans-10,cis-12-octadecadienoic acid (9 c,t-HPO), and 13-hydroperoxy-cis- 9,trans-11-octadecadienoic acid (13 c,t-HPO). GST A was more active with 9 c,t-HPO while GST B exhibited equivalent activity with both 9 c,t-HPO and 13 c,t-HPO. GST B exhibited glutathione conjugating activity toward 4- hydroxynonenal but GST A did not. Of the GST inhibitors examined, Cibacron blue was the most potent and, in general, the heterodimeric GST B was less sensitive to inhibitors. Both GST A and GST B are glycoproteins as indicated by binding of concanavalin A. The B2 subunit of GST B was more heavily glycosylated than the B1 subunit. Polyclonal antibodies raised against GST A exhibited cross-reactivity with the GST B1 subunit but not the B2 subunit. Comparisons of the N-terminal amino acid sequences of the GST A, B1, and B2 subunits with other theta, Type I GSTs indicated a high degree of sequence homology with maize GST I and a sugarcane GST.