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

P Casati,C.S Andreo,G.E Edwards,M.F Drincovich

doi:10.1590/s0100-879x1999001000002

Abstract

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.

Highlights

Light is essential for normal plant growth and development, as a source of energy and as a stimulus that regulates numerous developmental and metabolic processes by the induction of gene expression
The induction profile observed in Western blot analyses after treatment of maize seedlings with UV and different levels of photosynthetically active radiation (PAR) parallels the results obtained for the specific activity measurements for nicotinamide adenine dinucleotide phosphate-malic enzyme (NADP-ME)
Red light is as effective as UV-B in inducing NADP-ME either when it is provided for a short period of time or for 6 h

Summary

Introduction

Light is essential for normal plant growth and development, as a source of energy and as a stimulus that regulates numerous developmental and metabolic processes by the induction of gene expression. NADP-ME activity of etiolated maize seedlings was markedly increased above constitutive levels after exposure to high PAR and low PAR supplemented with UV-B radiation (Table 1) [30]. The low specific activity (0.05 U/mg of total soluble protein) measured in extracts from etiolated plants can be attributed to the expression of the constitutive isoform and/or low levels of expression of the photosynthetic isoform in etiolated maize tissue [26] To determine whether these results were due to an increased synthesis of the enzyme, Western blot analyses using an antibody raised and purified against the photosynthetic isozyme of NADP-ME [26] and dot blots of total RNA were conducted with the different samples.

High Low

Relative specific activity

Findings

Discussion