«Membrane Storage» of the Red Alga Porphyridium cruentum During Nitrate- and Sulphate Starvation

The unicellular red alga Porphyridium cruentum was investigated by electron microscopy and morphometry under exponential growth conditions, nitrate and sulphate starvation and during regeneration to exponential growth. Lipid bodies and one plastoglobule type are formed by aggregation and fusion of cellular membranes; these membranes are derived either from excessively produced smooth endoplasmic reticulum under normal growth conditions, or by a collapse of phycobilisome-depleted thylakoids under starvation conditions. Lipid bodies function as a «membrane component store» which is used for rapid membrane synthesis during regeneration. A second type of plastoglobule is formed at tubular structures, homologous to lipid bodies of higher plants. A model for the formation and degradation of lipid bodies is presented.