The impact of nitrogen deficiency and subsequent recovery on the photosynthetic performance of the red macroalga Gracilariopsis lemaneiformis

Abstract

The effect of nitrogen deficiency and subsequent recovery on photosynthetic performance of the red macroalga Gracilariopsis lemaneiformis was measured in terms of algal growth rate, accumulation of photosynthetic pigments (i.e., phycoerythrin and chlorophyll-a), maximum effective quantum yield of photosystem II (Fv/Fm), and the transcript levels of genes related to photosynthesis and photorespiration. Nitrogen deficiency and then recovery notably promoted the growth of G. lemaneiformis, significantly inhibited the accumulation of phycoerythrin and chlorophyll-a, but had no significant influence on Fv/Fm. In addition to physiological performance of algae under nitrogen stress, the key genes encoding photorespiratory and photosynthetic enzymes (i.e., gdct, gdcp, hpr, shmt, sgat, sbp, and rub) were up-regulated which might have led to more increased in growth rate than that of control after the recovery of nitrogen. While the down-regulation of gdct, gdcp, and shmt genes at the 4th day of nitrogen deficiency might be linked to the reduced accumulation of phycoerythrin and chlorophyll-a, the up-regulation of gdct and gdcp at the beginning of nitrogen deficiency and nitrogen recovery might associate with Fv/Fm that did not change significantly. Briefly, the up- and down-regulation of these genes at different times might be due to an algal complex regulatory mechanism. Thus, the combined action of these genes allows the algae to display higher photosynthetic efficiency and better growth, eventually acclimate to the varying environmental stresses. The data provided here represent a rich source for exploring the function of genes related to photorespiration and photosynthesis as well as the mechanism of algal acclimation under environmental stress.