Physiological effects of nitrogen deficiency and recovery on the macroalga Gracilariopsis lemaneiformis (Rhodophyta).

Algal metabolites are the most promising feedstocks for bio-energy production. Gracilariopsis lemaneiformis seems to be a good candidate red alga for polysaccharide production, especially relating to the agar production industry. Nitrogen deficiency is an efficient environmental pressure used to increase the accumulation of metabolites in algae. However, there are no studies on the physiological effects of G. lemaneiformis in response to nitrogen deficiency and its subsequent recovery. Here we integrated physiological data with molecular studies to explore the response strategy of G. lemaneiformis under nitrogen deficiency and recovery. Physiological measurements indicated that amino acids and protein biosynthesis were decreased, while endogenous NH and soluble polysaccharides levels were increased under nitrogen stress. The expression of key genes involved in these pathways further suggested that G. lemaneiformis responded to nitrogen stress through up-regulation or down-regulation of genes related to nitrogen metabolism, and increased levels of endogenous NH to complement the deficiency of exogenous nitrogen. Consistent with the highest accumulation of soluble polysaccharides, the gene encoding UDP-glucose pyrophosphorylase, a molecular marker used to evaluate agar content, was dramatically up-regulated more than 4-fold compared to the relative expression of actin after 4 d of nitrogen recovery. The present data provide important information on the mechanisms of nutrient balance in macroalgae.