This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via CrossRef Citing Articles via Google Scholar Google Scholar Articles by Chimiklis, P. E. Articles by Karlander, E. P. Search for Related Content PubMed PubMed Citation Articles by Chimiklis, P. E. Articles by Karlander, E. P. Agricola Articles by Chimiklis, P. E. Articles by Karlander, E. P.

Articles

Light and Calcium Interactions in Chlorella Inhibited by Sodium Chloride ^1,2

^a Department of Botany, University of Maryland, College Park, Maryland 20742

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.

Increasing light intensities from 2.7 to 9.4 to 14 mw/cm² decreased intracellular Na⁺ in cells cultured in 0.3 M NaCl medium without added Ca²⁺ and increased Cl^– uptake in cells cultured in 0.3 M NaCl medium with and without added Ca²⁺. For cells cultured in 0.3 M NaCl medium at 14 mw/cm² intracellular Na⁺ was 0.68 meq/g dry weight with Ca²⁺ added and 0.81 meq/g dry weight without Ca²⁺ added. Addition of Ca²⁺ at 2.7 mw/cm² reduced intracellular Na⁺ to similar values. It is postulated that energy requirements for active Na⁺ exclusion were reduced by addition of Ca²⁺ allowing more energy to be used for cell growth resulting in increased growth rates.

O₂ evolution and CO₂ fixation studies indicated that increased photosynthetic energy, probably actuated by a high proton gradient accompanying Cl^– influx and uncoupled from CO₂ fixation, was available for maintenance of cellular integrity and active control of intracellular ionic ratios. The O₂ evolving capacity was destroyed at 12 and 29 mw/cm² for cells cultured in 0.3 M NaCl medium respectively with and without the addition of Ca²⁺. Control cultures continued producing O₂ at light intensities up to 115 mw/cm².

¹ This investigation was supported in part by the National Aeronautics and Space Administration through NASA Grant NSG-70-60 and a Graduate Research Traineeship, and the Maryland Agriculture Experiment Station Project K-11.

² Scientific article No. A1756, contribution No. 4541, Maryland Agriculture Experiment Station.