UV-B, RED AND FAR-RED LIGHT REGULATE INDUCTION OF THE C-4 ISOFORM OF NADP-MALIC ENZYME IN ETIOLATED MAIZE SEEDLINGS

The induction of NADP-malic enzyme (NADP-ME) in maize (Zea mays) etiol ated seedlings as a function of intensity and duration of exposure to UV-B radiation was investigated by measuring changes in activity and p rotein, as well as by levels of NADP-ME gene transcripts. Exposures to UV radiation from 2 to 60 min including photon flux densities of UV-B of 0.5-2 mu mol quanta m(-2) s(-1) which are well below levels which occur naturally under full sunlight, caused an increase in Me gene mRN A and NADP-ME protein, as well as in NADP-ME activity. A similar dosag e of UV-A radiation was ineffective. A low level of red light (10 mu m ol quanta m(-2) s(-1)) for only 5 min was also effective in inducing i ncreases in NADP-ME activity equivalent to that with UV-B radiation. A 5 min exposure to far red light (100 mu mol quanta m(-2) s(-1)) follo wing UV-B or red light treatment largely reversed the induction of NAD P-ME, and this effect of far-red could be eliminated by further treatm ent with UV-B or red light. These results indicate that physiological levels of UV-B radiation have a positive effect on induction of the sy nthesis of a photosynthetic enzyme which is involved in C-4 photosynth esis.