Photosynthetic function in Dunaliella tertiolecta (Chlorophyta) during a nitrogen starvation and recovery cycle

Phytoplankton can be exposed to periods of N starvation with episodic N resupply. N starvation in Dunaliella tertiolecta (Butcher) measured over 4 days was characterized by slow reduction in cell chl and protein content and chl/carotenoid ratio and a decline in photosynthetic capacity and maximum quantum yield of photosynthesis (F(v)/F(m)). In the early stages of N starvation, cell division was maintained despite reduction in cellular chl. Chl content was more sensitive than carotenoids to N deprivation, and cellular chl a was maintained preferentially over chl b under N starvation. NO(3)(-) resupply stimulated rapid and complete recovery of F(v)/F(m) (from 0.4 to 0.7) within 24 h and commencement of cell division after 10 h, although N-replete levels of cell chl and protein were not reestablished within 24 h. Recovery of F(v)/F(m) was correlated with increases in cell chl and protein and was more related to increases in F(m) than to changes in F(0). Recovery of F(v)/F(m) was biphasic with a second phase of recovery commencing 4-6 h after resupply of NO(3)(-). Uptake of NO(3)(-) from the external medium and the recovery of F(v)/F(m), cell chl, and protein were inhibited when either cytosolic or chloroplastic protein synthesis was inhibited by cycloheximide or lincomycin, respectively; a time lag observed before maximum NO(3)(-) uptake was consistent with synthesis of NO(3)(-) transporters and assimilation enzymes. When both chloroplastic and cytosolic translation was inhibited, F(v)/F(m) declined dramatically. Dunaliella tertiolecta demonstrated a capacity to rapidly reestablish photosynthetic function and initiate cell division after N resupply, an important strategy in competing for limiting inorganic N resources.