A light-induced β-1,3-glucan breakdown associated with the differentiation of chloroplasts in Euglena gracilis

Abstract

1. Light induced a rapid breakdown of β-1,3-glucan in carbon-starved cells of Euglena gracilis, Strain Z. In contrast, β-1,3-glucan was utilized slowly in cells deprived of carbon growth substrates and maintained in the dark. 2. The breakdown of β-1,3-glucan required continuous light. At a low light intensity (7 ft candles), induction of the breakdown was delayed 12–24 h. 3. Cells showing a rapid breakdown of β-1,3-glucan contained high activities of the enzymes β-1,3-glucan phosphorylase and β-1,3-glucan hydrolase (EC 3.2.1.6) and a low activity of β-1,3-glucan synthetase (EC 2.4.1.12). 4. The light-induced breakdown of β-1,3-glucan appeared to be associated with the development of chloroplasts. A bleached mutant, ZUV-3, which cannot synthesize pigments when exposed to light, did not show a light-induced breakdown of β-1,3-glucan. 5. Chloramphenicol and 5-fluorouracil, inhibitors of the synthesis of a number of chloroplast proteins, did not inhibit the light-induced breakdown of β-1,3-glucan. Cycloheximide, an inhibitor of cytoplasmic protein synthesis, slightly delayed the breakdown. 6. An inhibitor of photosynthesis, 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), only partially inhibited chloroplast development during the period of rapid breakdown of β-1,3-glucan. After the store of β-1,3-glucan had been depleted, DCMU completely inhibited chloroplast development. The requirement for either photosynthesis or an endogenous supply of β-1,3-glucan for chloroplast development could be satisfied by supplying glucose exogenously.