Exogenous methyl jasmonate enhances lipid production in Isochrysis galbana under nitrogen deprivation and high light

Abstract

Nitrogen deprivation under high light is the most employed cultivation condition for the lipid's accumulation in microalgae. However, nitrogen deprivation causes the over-reduction of the photosystem (PS) II acceptor side in the presence of high light, confirmed by an increased VJ (the relative variable fluorescence at J-step) during cultivation. This in turn results in photo-inhibition of microalgal cells and photodamage to cellular metabolism which hinders the lipid production. To explore modifications for lipid accumulation, the exogenous methyl jasmonate (MeJA) effect was investigated on antioxidant capacity and lipid accumulation in Isochrysis galbana. Treatment with MeJA under high light nitrogen deprivation, (100 μM concentration), significantly enhanced the activity of ribulose-1,5-bisphosphate carboxylase/oxygenase, and facilitated the electron transport in photosynthesis as indicated by increased ΦPSII (effective quantum yield of PSII) after MeJA treatment. The exogenous MeJA increased the antioxidant potential of related enzymes (ascorbate peroxidase and superoxide dismutase) and significantly alleviated the accumulation of reactive oxygen species (ROS) under high light nitrogen deprivation for improved cell survival and cellular metabolism in I. galbana. The improved cellular metabolism further increased the pyruvate content, which can be converted into acetyl coenzyme A (an important precursor for fatty acid synthesis). MeJA addition increased the substrate pool required for fatty acid and lipid production. Overall, exogenous MeJA enhanced lipid production in I. galbana under high light nitrogen deprivation by regulating the antioxidant capability and biosynthesis of the substrate.