Effects of Nitrate toxicity on free Proline accumulation, chlorophyll degradation and photosynthetic efficiency in the green alga Chlorella vulgaris

Abstract

The effects of high nitrate concentrations on alterations in maximal photochemical efficiency of PSII ratio (Fv/Fm), chlorophyll content, chlorophyll degradation, growth rate and proline accumulation in Chlorella vulgaris Beyerinck [Beijerinck] were investigated in this study. The Fv/Fm ratio was observed in response to the increased nitrate concentration. The Fv/Fm ratio decreased in C. vulgaris following 44 h in 12.99 mM NaNO3-enriched media. Experimental results showed that, growth rates and chlorophyll content declined by increasing nitrate concentration. The decrease in the ratio of chlorophyll a/b with enrichment of high nitrate concentration (6.5 mM and 12.99 mM NaNO3) was also caused by a decrease in chlorophyll a and an increase in chlorophyll b concentration in C. vulgaris cultures. The results showed that 6.5 and 12.99 mM nitrate concentration increased proline content in treated cells, which suggests that nitrate stress lead to proline accumulation in C. vulgaris. © IJSM 2019.