Tunicamycin suppresses differentiation and stimulates dedifferentiation of heterocysts in the cyanobacteriumAnabaena azollae Stras

Abstract

The effect of tunicamycin (TM), a specific inhibitor of glycosylation of proteins, on heterocyst differentiation inAnabaena azollae Stras. was investigated. Heterocysts were developed in the presence of TM up to a concentration of 0.2 μg ml⁻¹, whereas at higher concentrations differentiation proceeded only up to the proheterocyst stage. Analysis of lipids by thinlayer chromatography showed that the glycolipid that is specific for the laminated layer of mature heterocysts was synthesized even in the cultures where the differentiation had proceeded only up to the early proheterocyst stage (i.e., at>0.2 μg TM ml⁻¹). Further, deposition of the glycolipid-containing laminated layer in the envelope of the heterocysts differentiated in the presence of TM (i.e., at ≤0.2 μg ml⁻¹) was incohesive as observed at the ultrastructural level. These findings clearly suggest that the process leading to the transportation of the heterocyst-specific glycolipid and its deposition as a laminated layer are affected by TM treatment. Because of the reported highly selective mode of action of TM, our results implicate a role for protein glycosylation in the process of heterocyst development and maturation.

Although the heterocyst is a terminal stage of differentiation, because they normally do not divide/multiply, a considerable percentage of heterocysts that developed in the presence of TM dedifferentiated. The aberrations formed in the laminated layer, probably because of the inhibition of protein glycosylation owing to TM treatment, may have contributed to the instability of heterocyst structure and consequently led to their dedifferentiation.