Effect of Temperature and Safeners on Glutathione Levels and Glutathione S-Transferase Activity in Maize

Studies were conducted to determine the biochemical aspects of chloroacetamide injury to maize and the mechanism by which safeners maintain herbicide tolerance, even at reduced temperatures. The objectives of these studies were threefold: one, determine whether gluta­thione (GSH) content varies in maize plants grown at three different temperatures in safener-treated and non-treated plants; two, determine whether glutathione S-transferase (GST) activ­ity varies in plants grown at different temperatures; and three, determine if GSH activity is sensitive to low temperatures in vitro. The herbicide safeners CGA -154281 [4-(dichloroacetyl)-3,4-dihydro-3-methyl-2 H-1 ,4-benzoxazine] and dichlormid [2,2-dichloro-N,N-di-2-propenylacetamide] were used with metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-n-(2-methoxy-1-methyl)acetamide] or acetochlor [2-chloro-N-(ethoxymethyl)-N-2-ethyl-6-methylphenyl)-acetamide], respectively, to determine the mechanisms of maize tolerance. CGA -154281 signifi­cantly increased GSH levels in maize seedlings grown at 27 °C compared to non-safened seed­lings, however significant differences were not seen at 17 or 37 °C. Dichlormid increased GSH levels by 1.6-fold at all growth temperatures. Both CGA -154281 and dichlormid increased GST activity significantly at all growth temperatures. The safener-induced GST activity was main­tained at in vitro incubation temperatures of 5 and 15 °C for acetochlor and metolachlor, re­spectively. In contrast, GST activity from non-safened tissue was essentially absent at these temperatures. Therefore, greater GST activity following safener treatment may result in higher levels of herbicide metabolism, even at low temperatures.