UV-B, red and far-red light regulate induction of the C4 isoform of NADP-malic enzyme in etiolated maize seedlings

The induction of NADP-malic enzyme (NADP-ME) in maize (Zea mays) etiolated seedlings as a function of intensity and duration of exposure to UV-B radiation was investigated by measuring changes in activity and protein, 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 mRNA and NADP-ME protein, as well as in NADP-ME activity. A similar dosage of UV-A radiation was ineffective. A low level of red light (10 mu mol quanta m(-2) s(-1)) for only 5 min was also effective in inducing increases 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)) following UV-B or red light treatment largely reversed the induction of NADP-ME, and this effect of far-red could be eliminated by further treatment with UV-B or red light. These results indicate that physiological levels of UV-B radiation have a positive effect on induction of the synthesis of a photosynthetic enzyme which is involved in C-4 photosynthesis.