Evolution in the photosynthetic oxygen rate of a Cd-resistant strain of Dictyosphaerium chlorelloides by changes in light intensity and temperature

Abstract

Environmental factors such as temperature and light are the most determinants in the photosynthetic productivity in microalgae. However, under extreme of these conditions, certain resistant microalgae strains possess additional abilities such as growth in the presence of high concentrations of metals and some can improve in combinations of more than one abiotic stress. Therefore, the aim of this research was to evaluate the efficiency in photosynthetic production through the oxygen balance to variations in photon intensity, and under temperature changes in a Cd-resistant strain (Dc^RCd100) compared to the wild-type strain (Dc1M^wt) of Dictyosphaerium chlorelloides. The results showed that the Dc^RCd100 strain has the maximum efficiency at 200 μmol m^-2 s^-1 on photosynthesis net (Pn) (96.32 ± 3.63% nmol O₂ ml^-1 min^-1) as the threshold light saturation, and an adaptation to maintain this maximum photosynthetic gross (Pg) rate at 30 °C (94.99 ± 10.03% nmol O₂ ml^-1 min^-1) due to possible modifications in the photosynthetic apparatus that is reflected in the net evolution rate of O₂ to deal with such evaluated conditions. While, Dc1M^wt strain its maximum photosynthetic efficiency was at 300 μmol m^-2 s^-1 and 21 °C (97.72 ± 2.99 and 99.85 ± 0.30%nmol O₂ ml^-1 min^-1, respectively) and in optimal response to the oxygen balance that is normally achieved by this mesophilic genus. These results provide a new prediction of mechanisms in the oxygen evolution in photosynthesis that rules the correlation between resistance and adaptation to extreme abiotic conditions in metal resistant strains of eukaryotic microalgae.

Keywords: Cadmium resistance; Dictyosphaerium chlorelloides; Light threshold saturation; Photon intensity; Photosynthetic efficiency; Temperature.