In Vivo Nitrate Reduction in Roots and Shoots of Barley (Hordeum vulgare L.) Seedlings in Light and Darkness.

In vivo NO(3) (-) reduction in roots and shoots of intact barley (Hordeum vulgare L. var Numar) seedlings was estimated in light and darkness. Seedlings were placed in darkness for 24 hours to make them carbohydrate-deficient. During darkness, the leaves lost 75% of their soluble carbohydrates, whereas the roots lost only 15%. Detached leaves from these plants reduced only 7% of the NO(3) (-) absorbed in darkness. By contrast, detached roots from the seedlings reduced the same proportion of absorbed NO(3) (-), as did roots from normal light-grown plants. The rate of NO(3) (-) reduction in the roots accounted for that found in the intact dark-treated carbohydrate-deficient seedlings. The rates of NO(3) (-) reduction in roots of intact plants were the same for approximately 12 hours, both in light and darkness, after which the NO(3) (-) reduction rate in roots of plants placed in darkness slowly declined. In the dark, approximately 40% of the NO(3) (-) reduction occurred in the roots, whereas in light only 20% of the total NO(3) (-) reduction occurred in roots. A lesser proportion was reduced in roots because the leaves reduced more nitrate in light than in darkness.