Regolazione dell'assorbimento dell'ammonio nell'alga unicellulare Cyanidium caldarium

Di Martino Rigano, Vittoria ; Vona, Vincenza ; Manzo, Luigi ; Di Martino, Catello ; Rigano, Carmelo

Atti della Accademia nazionale dei Lincei. Rendiconti della Classe di scienze fisiche, matematiche e naturali, Série 8, Tome 81 (1987) no. 3, pp. 305-315

Résumé

Cells of Cyanidium caldarium, a unicellular acidophilic thermophilic non-vacuolate red alga, cultivated in batch under conditions of excess ammonium assimilated ammonium at a rate of $0,32 \,\mu mol/h/mg$ cell dry weight, and assimilation was up to 85% inhibited in darkness. By contrast, cells grown in chemostat under conditions of nitrogen limitation assimilated ammonium at a 3-fold higher rate, and assimilation was only 34% inhibited in darkness. Assimilation of ammonium was linear with time with all type of cells and under all the conditions tested. Batch-grown cells submitted to conditions of nitrogen starvation attained, after about 72 h, a 3-fold higher capacity to assimilate ammonium; beside, these N-starved cells, like N-limited chemostat cells, assimilated ammonium also in the dark at a rate which was only 15% lower than in the light. After ammonium addition (and assimilation), the capacity of these cells to take up ammonium costantly decreased in the time during 7 h period of light/dark cycles. However, the loss of capacity was less pronounced in the light and it was almost total in the dark. It is suggested that these variations in the overall capacity and in the pattern of ammonium assimilation in light and darkness in cells submitted to different nitrogen conditions depend on control phenomena which involve the partecipation of two distinct uptake systems, or of two glutamine synthetase/glutamate synthase systems, sharing different regulatory properties.