Influence of UV-A or UV-B light and of the nitrogen source on the induction of ferredoxin-dependent glutamate synthase in etiolated tomato cotyledons

The influence of ultraviolet A (UV-A) or B (UV-B) light and of the nitrogen source on the induction of ferredoxin-dependent glutamate synthase (Fd-GOG AT, EC 1.4.7.1) was examined in etiolated cotyledons of tomato (Lycopersico n esculentum L.). The Fd-GOGAT activity increased upon illumination of etio lated tomato cotyledons with UV-A or UV-B light. This stimulation of Fd-GOG AT activity was correlated with an increase in both the Fd-GOGAT transcript level and the Fd-GOGAT protein abundance. These results suggest that W-A o r W-B light stimulates the de novo synthesis of Fd-GOGAT in etiolated tomat o cotyledons. Both UV-A and UV-B Light failed to influence the activity of NADH-GOGAT (EC 1.4.1.14) in etiolated tomato cotyledons. Taken together, ou r data indicate that the tomato genes encoding Fd- or NADH-dependent glutam ate synthase are regulated differently by W-A or UV-B light. No difference with respect to both the Fd-GOGAT transcript and protein abundance was foun d between cotyledons of tomato seedlings grown with either nitrate or ammon ium as the sole N-source in the dark or in white light. In addition, the in crease in the Fd-GOGAT protein pool induced by white light in etiolated nit rate-grown tomato seedling cotyledons was similar to that induced by white light in etiolated ammonium-grown tomato seedling cotyledons. These results show that the tomato Fd-GOGAT protein level does not depend strongly on th e nature of the nitrogen source and that there appears to be no major stimu latory effect on the Fd-GOGAT protein pool produced by nitrate during the i llumination of etiolated tomato cotyledons. (C) Elsevier, Paris.