The effect of nitrogen starvation on the ultrastructure and pigment composition of chloroplasts in the acidothermophilic microalga Galdieria sulphuraria

We studied the effect of nitrogen starvation on growth indices, vitality, ultrastructure, and the photosynthetic apparatus of unique acidothermophilic microalga Galdieria sulphuraria (Galdieri) Merola. Long-term nitrogen starvation ceased G. sulphuraria growth and cell division. During the first days of starvation, phycobiliproteins degraded first, then the content of chlorophyll and carotenoids decreased to trace amounts, chloroplast reduced, cell wall became thinner, and storage compounds accumulated. However, the cells were alive. A comparison with the effects of nitrogen starvation on other photosynthesizing organisms showed that suppression of cell division, reduction of the photosynthetic apparatus to some minimum, and accumulation of storage compounds are a universal response to this stress.