Inhibition of nitrate reductase by azide in microalgae results in triglycerides accumulation

Sodium azide (Az) induces accumulation of triglycerides (TAG) in the green alga Chlorella desiccata with minimal growth retardation (Rachutin-Zalogin & Pick, joint manuscript). To clarify the mechanism of this effect, the involvement of respiration, production of reactive oxygen species (ROS) and suppression of nitrate reductase (NR) was investigated. Different respiratory inhibitors induced minor or no TAG accumulation, ruling out respiration as the primary Az target. ROS generators failed to induce massive TAG accumulation, but the singlet oxygen quencher DABCO inhibited Az-induced TAG biosynthesis and this inhibition was suppressed in 30% D2O. Az-induced TAG accumulation was observed in nitrate, but not in ammonium medium, in which growth is not dependent on NR. Effects of cyanide, cyanate, a singlet oxygen quencher, D2O and of CO2 limitation on TAG accumulation are consistent with inhibition of NR. C. desiccata NR activity is Az-sensitive. The results suggest that Az-induced TAG accumulation results primarily from photoinactivation of NR.

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