Reinvestigation of the proposed red light effect on carotenogenesis in the fungus Verticillium agaricinum

The activities of glutamine synthetase (EC 6.3.1.2) and glutamate dehydrogenase (EC 1.4.1.2) appear to be inversely related in their distribution among the different tissues of 40-day-old tomato plants ( Lycopersicon esculentum L. cv. Hellfrucht Frühstamm), glutamine synthetase activity being highest in the leaves and glutamate dehydrogenase activity in the root. Leaf glutamine synthetase activity decreases with plant growth and shows diurnal variation with a maximum in the light and a minimum in the dark. In vitro, the activity of purified glutamine synthetase increases with the energy charge of the assay medium and decreases with increasing concentrations of p -chloromercuribenzoic acid. Glutamine synthetase activity in the plant may be regulated by physiological changes occurring during the light-dark transition periods.