Nitrate reductase activity and nitrogenous gas evolution from heterotrophic, photomixotrophic and photoautotrophic soybean suspension cultures

Abstract

Soybean ( Glycine max L. Merr. cv. Corsoy) suspension cultures were grown hetertrophically (3% sucrose, dark), photomixotrophically (1% sucrose, light), and photoautotrophically (no sucrose, light) to determine if constitutive and inducible nitrate reductase (NR) activities were expressed (both activities are expressed in intact plants). Nitrogenous gas evolution, a marker for the constitutive activity in soybean leaves, was not detected in any of the cultures at any time during the 14-day subculture period. Moreover, photomixotrophic and heterotrophic cells grown on glutamine as a nitrogen source had no detectable NR. Cells grown on nitrate contained NR activity with an apparent K m (NO 3 −) identical to that of the inducible activity from soybean leaves, and glutamine did not express this activity. It was concluded that constitutive NR was not expressed in soybean suspension culture regardless of age, nitrogen source, or photosynthetic capability, while inducible NR activity was expressed with nitrate nutrition. The implications of these findings, in terms of using suspension cultures to select NR deficient soybean lines for possible regeneration, are discussed.