Abstracts Biological Sciences

Physiological and Biochemical Adaptation in the Nitrogen Nutrition of Spirodela Oligorrhiza

by A. R. (Allan Ross) Ferguson

Summary: 1. A Study was made of some aspects of the utilization by Spirodela oligorrhiza of ammonium, nitrate, nitride, and organis nitrogenous compounds as sole sources of nitrogen. 2. S. oligorrhiza was grown in axenci culture under carefully defined conditions, and the only factor to be consciously varied were those relating to the nitrogen source. 3. Ammonium, or some product of assimilation, inhibited the utilization of nitrate by inhibiting, at least partially, the uptake of nitrate, and by inhibiting almost completely the reduction of nitrate to nitrite. 4. Nitrite also inhibited the utilization of nitrate. 5. Ammonium and nitrite were taken up and assimilated simultaneously when they were supplied together in the medium. 6. Nitrate reductase and nitrite reductase were found to be adaptive enzymes, being present in S. ologorrhiza only when it was supplied with nitrate or nitrite. There was good correlation between the concentration of nitrate in plants and the level of nitrate reduction that they contained...