Light and Calcium Interactions in Chlorella Inhibited by Sodium Chloride 12

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Analysis of NaCl toxicity in Chlorella sorokiniana showed decreased growth rates, increased dry weight per cell, increased intracellular Na+ and Cl−, more total chlorophyll per cell, a decreased chlorophyll a to chlorophyll b ratio, increased rates of O2 evolution, and decreased rates of CO2 fixation when the extracellular concentration of NaCl was increased from zero to 0.3 m. Cultures did not grow at concentrations greater than 0.3 m NaCl unless 10 mm calcium salts were present. Inclusion of that concentration of Ca2+ extended the tolerance to 0.5 m NaCl before growth stopped. Increasing the light intensity from 1.2 to 9.4 mw/cm2 increased growth rates for cultures in 0.10 to 0.45 m NaCl. At 14 mw/cm2 added Ca2+ reduced growth rates of cultures in 0.3 m NaCl compared to controls without added Ca2+. Maximal growth rates for cultures in NaCl media were achieved by addition of 10 mm CaSO4 and maintenance of the light intensity at 9.4 mw/cm2. The maximal growth rate of the organism was 9.6 doublings/day achieved at 2.7 mw/cm2 for control cultures. In 0.3 m NaCl the growth rate was 4.3 doublings/day at 2.7 mw/cm2 and 8.2 doublings/day at 9.4 mw/cm2 with 10 mm CaSO4 added.

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