Recovery of growth capacity and of chloroplast transglutaminase activity induced by polyamines in a polyamine-deficient variant strain of Dunaliella salina

The variant strain of Dunaliella salina is characterised by: a) a very low growth capacity; b) a deficiency in polyamines, transglutaminase chlorophyll, and protein content; and c) an unbalanced putrescine/spermidine ratio. A supply of 100 μmol/L putrescine or 1 mmol/L ornithine induces the resumption of growth. Putrescine has several additional effects: endogenous putrescine and spermidine levels increase and their ratio reaches 1.6, a value typical of the growing wild type; chlorophyll aand b also increase and their ratio (3.6) becomes close to that of the wild type (3.0); protein content increases, especially in the chloroplast. Transglutaminase(s) in chloroplasts of putrescine-treated algae is stimulated and increases its conjugating activity by 9-fold in the light and less than 3-fold in the dark when compared to untreated controls. The role of polyamines in improving the physiological condition of the chloroplast and their effect on growth are discussed.