Regulation of the expression of NADP-malic enzyme by UV-B, red and far-red light in maize seedlings

• Main Authors: P. Casati, M.F. Drincovich, G.E. Edwards, C.S. Andreo
• Format: Article
• Language: English
• Published: Associação Brasileira de Divulgação Científica 1999-10-01
• Series: Brazilian Journal of Medical and Biological Research
• Subjects: C4 photosynthesis; NADP-malic enzyme; UV-B radiation; photosynthesis; red light; far-red light
• Online Access: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-879X1999001000002
• ISSN: 0100-879X; 1414-431X

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.