Effects of Light on Chlorophyll Formation in Cultured Tobacco Cells II. Blue Light Effect on 5-Aminolevulinic Acid Formation1

Abstract

5-Aminolevulinic acid (ALA) accumulation in dark-grown tobacco callus cells in the presence of levulinic acid (LA) was followed under blue or red light or in continuous darkness. Significant formation of ALA continued in the dark. The protochlorophyll- (ide) (Pchl) content of dark-incubated cells remained low because of its turnover. We inferred that the feedback inhibition of ALA synthesis by Pchl would not occur in darkincubated callus cells. ALA formation was enhanced by blue light, and this effect reached saturation at an intensity of about 800 mW.m−2. Neither weak nor strong red light affected ALA formation. Full enhancement of ALA formation by blue light was attained after fairly long continuous illumination of the callus cells. This blue lightenhanced activity of ALA synthesis declined very slowly during the subsequent dark incubation. The blue light enhancement of ALA formation was observed in callus cells supplied with sucrose over a wide range of concentrations. Pchl regeneration in carbon-starved callus cells, supplied with glutamate at various concentrations, was also markedly enhanced by blue light. Respiration of the callus cells was not enhanced by blue light. A possible role of blue light in regulating ALA formation in callus cells is discussed.