Multiple effects of salinity on photosynthesis of the protist Euglena gracilis

Abstract

The effect of NaCl in the culture medium on growth, photosynthesis and cell content of chlorophyll, K+, Na+, Ca2+ and Mg2+ in Euglena gracilis was studied. O2 production, quantum yield of photosystem II (PSII), the non‐photochemical quenching of chlorophyll fluorescence (qN) and the chlorophyll alb ratio all diminished by 0.2 M NaCl. Respiration and chlorophyll a and b increased, whereas the photochemical quenching (qp) of chlorophyll fluorescence was not affected by 0.2 M NaCl. Salt stress also induced an increase in cell volume and in K+ and Na+ concentrations, but decreased the concentrations of Ca2+ and Mg2+. Except for a protective effect on O2 production, additional Ca2+ in the culture medium did not attenuate the salt effect on the parameters measured. The addition of HCO3− restored the PSII quantum yield of O2 production in cells grown in high salt. Salt stress promoted a decrease in the apparent rate of quinone A (QA) reduction and an apparent obstruction of QB reduction, which were not prevented by excess HCO3−; the addition of 3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea (DCMU) did not increase chlorophyll fluorescence in salt‐grown cells. These results indicate that photosynthesis in Euglena grown under salt stress exhibits: (1) diminution of the HCO3− dependent water‐splitting activity of PSII; (2) inhibition of the electron transfer at the quinone pool level; (3) probable increase in thylakoid stacking (as indicated by the effect on the chlorophyll alb ratio); and (4) dissipation of the H+ gradient across the thylakoid membranes (as indicated by the decrease of qN).

Anthracene phytotoxicity in the freshwater flagellate alga Euglena agilis Carter

“…We assume that a severe reduction in the photosynthetic process at high anthracene levels likely reduces the magnitude of the pH gradient, thereby affecting NPQ values, consistent with the view of González–Moreno et al . 47 who reported similar observations on fluorescence quenching in E. gracilis under salt stress. Severe reduction in F v / F m of E. gracilis exposed to NaCl had resulted in a diminution of the pH gradient across the thylakoid membranes and subsequently, up to 95% reduction in NPQ 47 .…”

Cytosol–mitochondria transfer of reducing equivalents by a lactate shuttle in heterotrophic Euglena

“…By comparison, Euglena accumulated high levels of d ‐ and l ‐lactate (up to 80 m m in glucose‐grown cells), but growth was similar to that achieved by lactate‐grown cells, which accumulated a much lower level of lactate (Figs 1 and 3). Thus, an inverse correlation was rather found between lactate accumulation and internal water volume, in which the synthesis and discharge of metabolites such as trehalose [34], or balancing the Na + and K + concentrations [17], probably attenuated osmotic stress.…”

“…The distribution of [ 3 H]-H 2 O and 3 H-labeled inulin across the plasma membrane was used to determine the intracellular water volume [17]. Cells (1 · 10 7 ), cultured with different carbon sources and harvested at different times of culture, were washed once in SHE buffer.…”

First Report of Pseudobodo sp, a New Pathogen for a Potential Energy-Producing Algae: Chlorella vulgaris Cultures

“…6B). With regard to the salinity effects on protists, Moreno described multiple effects of salinity on the photosynthesis of the protist Euglena gracilis [68]. However unlike Euglena gracilis, Pseudobodo sp.…”