Regulation of the expression of NADP-malic enzyme by UV-B, red and far-red light in maize seedlings.
The induction of nicotinamide adenine dinucleotide phosphate-malic enzyme (NADP-ME) in etiolated maize (Zea mays) seedlings by UV-B and UV-A radiation, and different levels of photosynthetically active radiation (PAR, 400-700 nm) was investigated by measuring changes in activity, protein quantity and RNA levels as a function of intensity and duration of exposure to the different radiations. Under low levels of PAR, exposure to UV-B radiation but not UV-A radiation for 6 to 24 h caused a marked increase in the enzyme levels similar to that observed under high PAR in the absence of UV-B. UV-B treatment of green leaves following a 12-h dark period also caused an increase in NADP-ME expression. Exposure to UV-B radiation for only 5 min resulted in a rapid increase of the enzyme, followed by a more gradual rise with longer exposure up to 6 h. Low levels of red light for 5 min or 6 h were also effective in inducing NADP-ME activity equivalent to that obtained with UV-B radiation. A 5-min exposure to far-red light following UV-B or red light treatment reversed the induction of NADP-ME, and this effect could be eliminated by further treatment with UV-B or red light. These results indicate that physiological levels of UV-B radiation can have a positive effect on the induction of this photosynthetic enzyme. The reducing power and pyruvate generated by the activity of NADP-ME may be used for respiration, in cellular repair processes and as substrates for fatty acid synthesis required for membrane repair.
Casati
P
P
Centro de Estudios Fotosintéticos y Bioquímicos, Universidad Nacional de Rosario, Rosario, Argentina.
Drincovich
M F
MF
Edwards
G E
GE
Andreo
C S
CS
D004790:Enzyme Induction; D008291:Malate Dehydrogenase / Q000378:metabolism / Q000528:radiation effects*; D010788:Photosynthesis / Q000528:radiation effects*; D012313:RNA / Q000378:metabolism / Q000528:radiation effects; D013997:Time Factors; D014466:Ultraviolet Rays; D003313:Zea mays / Q000201:enzymology / Q000528:radiation effects*
D012313:RNA; D008291:Malate Dehydrogenase; C031917:malate dehydrogenase (oxaloacetate-decarboxylating) (NADP+)