ENHANCEMENT OF MICROSOMAL BENTAZON 6-HYDROXYLASE AND CINNAMIC ACID 4-HYDROXYLASE ACTIVITIES FROM GRAIN-SORGHUM SHOOTS

Microsomes isolated from excised shoots of grain sorghum (Sorghum bicolor, (L.) Moench) seedlings arylhydroxylated bentazon herbicide and cinnamic acid to 6-hydroxybentazon and p-coumaric acid, respectively. Constitutive, unprotected bentazon 6-hydroxylase (EC 1.14.13.) activity was low but measurable, whereas, constitutive, unprotected cinnamic acid 4-hydroxylase (EC 1.14.13.11) activity was much greater and was easily measurable. Inclusion of the isolation medium additives (i.e., protectants) ascorbate (40 mM), P-mercaptoethanol (14 mM), and EDTA (10 mM) increased bentazon 6-hydroxylase and cinnamic acid 4-hydroxylase activities to levels 11.6 and 1.7 times the control activities, respectively. Naphthalic anhydride seed treatment induced bentazon 6-hydroxylase activity to a level 1.9 to 8.0 times the control activity, depending on the sorghum variety, but did not significantly induce cinnamic acid 4-hydroxylase activity in any variety. Isolation medium additives and naphthalic anhydride seed treatment independently enhanced bentazon 6-hydroxylase activity resulting in a combined increase in activity 21.3 times the control activity. Differential responses of bentazon 6-hydroxylase and cinnamic acid 4-hydroxylase to isolation medium additives and naphthalic anhydride seed treatment suggest that bentazon and cinnamic acid are hydroxylated by different microsomal monooxygenases in sorghum. (C) 1994 Academic Press, Inc.