UV-B INDUCTION OF NADP MALIC ENZYME IN ETIOLATED AND GREEN MAIZE SEEDLINGS

The effect of treatment of etiolated maize seedlings with UV-B and UV- A radiation, and different levels of photosynthetically active radiati on (PAR, 400-700 nm), on the activity and quantity of NADP-malic enzym e (NADP-ME) and on RNA levels was determined, Under low levels of PAR (14 mu mol m(-2) s(-1)), exposure to UV-B radiation (9 mu mol m(-2) s( -1)) but not UV-A radiation (11 mu mol m(-2) s(-1)) for 6-24 h caused a marked increase in the activity of the enzyme similar to that observ ed under high PAR (300 mu mol m(-2) s(-1)) in the absence of UV-B, Wes tern blot analysis indicated there was a specific increase of the phot osynthetically active isoform of the enzyme, This increase was also me asured at the RNA level by dot blot analysis, indicating that the indu ction is displayed at the level of NADP-ME transcription, UV-B treatme nt of green leaves after a 12 h dark period also caused an increase in the activity and level of NADP-ME. The W-B induction of NADP-RIE synt hesis may reflect a mechanism for induction of photosynthetic processe s in C-4 photosynthesis, Alternatively, the relatively low intensity o f UV-B radiation present under full sunlight might provide a signal th at facilitates repair of UV-B-induced damage through the increased act ivity of different enzymes such as NADP-ME. It is speculated that the reducing power and pyruvate generated by activity of NADP-ME may be us ed for respiration in cellular repair processes and as substrates for the fatty acid synthesis required for membrane repair.