Anaerobic nitrite production by plant cells and tissues: evidence for two nitrate pools

Tobacco (Nicotiana tabacum L. cv. Xanthi) XD cells containing nitrate and nitrate reductase stopped producing nitrite after approximately 1 hour when incubated under anaerobic conditions. The cessation of nitrite production was not due to an inactivation of the nitrate reducing system. This was shown by the ability of the cells to resume anaerobic nitrite production at a rate similar to the initial rate of nitrite production upon exposure to nitrate, monohydroxy alcohols or pyrazole. Cessation of nitrite production also could not be attributed to leakage of nitrate from the cells. Although some nitrate did leak from the cells, most of the nitrate was still in the cells by the time anaerobic nitrite production ceased. We infer the existence of a small metabolic pool and a large storage pool of nitrate, such that nitrite production ceases when the metabolic pool is depleted of nitrate. The metabolic pool of nitrate in tobacco cells decreased 170-fold as the culture aged from 3 to 5 days. However, total cellular nitrate during this period remained relatively constant.Anaerobic nitrite production by barley (Hordeum vulgare) aleurone layers and corn (Zea mays) leaf sections also ceased after only a small fraction of endogenous nitrate was reduced and resumed again upon addition of exogenous nitrate. In contrast to that found with tobacco cells, the metabolic pool of nitrate in corn leaf sections remained constant with age, while total endogenous nitrate increased. These results were interpreted to mean that higher plants in general contain metabolic and storage pools of nitrate, the properties of which vary with species and physiological variables.