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

5-Aminolevulinic acid (ALA) accumulation in dark-grown tobaccocallus cells in the presence of levulinic acid (LA) was followedunder blue or red light or in continuous darkness. Significantformation of ALA continued in the dark. The protochlorophyll-(ide) (Pchl) content of dark-incubated cells remained low becauseof its turnover. We inferred that the feedback inhibition ofALA synthesis by Pchl would not occur in darkincubated calluscells. ALA formation was enhanced by blue light, and this effectreached saturation at an intensity of about 800 mW.m^–2.Neither weak nor strong red light affected ALA formation. Fullenhancement of ALA formation by blue light was attained afterfairly long continuous illumination of the callus cells. Thisblue lightenhanced activity of ALA synthesis declined very slowlyduring the subsequent dark incubation. The blue light enhancement of ALA formation was observed incallus cells supplied with sucrose over a wide range of concentrations.Pchl regeneration in carbon-starved callus cells, supplied withglutamate at various concentrations, was also markedly enhancedby blue light. Respiration of the callus cells was not enhancedby blue light. A possible role of blue light in regulating ALAformation in callus cells is discussed. ¹Dedicated to the late Professor Joji Ashida. (Received September 3, 1982; Accepted April 5, 1983)