Formation of triacylglycerol in Nitzschia closterium f. minutissima under nitrogen limitation and possible physiological and biochemical mechanisms

This study aimed to investigate how the diatom Nitzschia closterium f. minutissima accumulates triacylglycerol (TAG) under nitrogen-limited stress. Algal cells were exposed to the nitrogen concentrations of 932, 712, 491, 270 and 159 μM. The results showed that low nitrogen condition caused significant decrease in chlorophyll a content and photosynthesis efficiency, and thereby inhibition of algal growth. Additionally, the soluble protein decreased at low nitrogen concentration, while the intracellular reactive oxygen species of all treatments increased largely in the stationary phase compared to the exponential phase. The main carbon resource may flow to synthesize TAG when proteins synthesis inhibition occurred. The pigment reduction and low growth rate contributed to TAG accumulation. However, the falling photosynthesis would slow down the rate of TAG formation, or even induce degradation of neutral lipid droplet. The accumulation of TAG seems to be a protective mechanism to help algal cells survive under nitrogen-limited stress.

Research Highlights
► This paper investigated triacylglycerol accumulation in N. closterium;
► low nitrogen causes significant decrease in chl a and photosynthesis efficiency;
► the soluble protein decreased at low nitrogen concentration;
► ROS of all treatments increased largely at stationary phase;
► accumulation of TAG seems to be a protective mechanism.