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Control of Diurnal Variations in Photosynthetic Products

II. Nitrate Reductase Activity

Division of Irrigation Research, Griffith, Commonwealth Scientific and Industrial Research Organization, New South Wales, Australia

Nitrate accumulates in the leaves of Capsicum annuum L. cv. California Wonder and the leaf content is dependent on the nitrate level supplied to the roots. There is no consistent diurnal periodicity in the leaf nitrate levels.

Nitrate reductase activity exhibits three distinct peaks in the leaves. One in the dark period, a second at the time of the prevailing dawn, and a third 6 hours after the beginning of the photoperiod. The third peak of activity can be induced by a short period of illumination (20 minutes) which is also sufficient to induce the labeling of the amino acid fraction by ¹⁴CO₂.