Chimiklis P E, Karlander E P
Department of Botany, University of Maryland, College Park, Maryland 20742.
Plant Physiol. 1973 Jan;51(1):48-56. doi: 10.1104/pp.51.1.48.
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 O(2) evolution, and decreased rates of CO(2) 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 Ca(2+) extended the tolerance to 0.5 m NaCl before growth stopped. Increasing the light intensity from 1.2 to 9.4 mw/cm(2) increased growth rates for cultures in 0.10 to 0.45 m NaCl. At 14 mw/cm(2) added Ca(2+) reduced growth rates of cultures in 0.3 m NaCl compared to controls without added Ca(2+). Maximal growth rates for cultures in NaCl media were achieved by addition of 10 mm CaSO(4) and maintenance of the light intensity at 9.4 mw/cm(2). The maximal growth rate of the organism was 9.6 doublings/day achieved at 2.7 mw/cm(2) for control cultures. In 0.3 m NaCl the growth rate was 4.3 doublings/day at 2.7 mw/cm(2) and 8.2 doublings/day at 9.4 mw/cm(2) with 10 mm CaSO(4) added.Increasing light intensities from 2.7 to 9.4 to 14 mw/cm(2) decreased intracellular Na(+) in cells cultured in 0.3 m NaCl medium without added Ca(2+) and increased Cl(-) uptake in cells cultured in 0.3 m NaCl medium with and without added Ca(2+). For cells cultured in 0.3 m NaCl medium at 14 mw/cm(2) intracellular Na(+) was 0.68 meq/g dry weight with Ca(2+) added and 0.81 meq/g dry weight without Ca(2+) added. Addition of Ca(2+) at 2.7 mw/cm(2) reduced intracellular Na(+) to similar values. It is postulated that energy requirements for active Na(+) exclusion were reduced by addition of Ca(2+) allowing more energy to be used for cell growth resulting in increased growth rates.O(2) evolution and CO(2) fixation studies indicated that increased photosynthetic energy, probably actuated by a high proton gradient accompanying Cl(-) influx and uncoupled from CO(2) fixation, was available for maintenance of cellular integrity and active control of intracellular ionic ratios. The O(2) evolving capacity was destroyed at 12 and 29 mw/cm(2) for cells cultured in 0.3 m NaCl medium respectively with and without the addition of Ca(2+). Control cultures continued producing O(2) at light intensities up to 115 mw/cm(2).
对索氏小球藻中氯化钠毒性的分析表明，当细胞外氯化钠浓度从零增加到0.3m时，生长速率降低、每细胞干重增加、细胞内Na⁺和Cl⁻增加、每细胞总叶绿素增加、叶绿素a与叶绿素b的比率降低、O₂释放速率增加以及CO₂固定速率降低。除非存在10mm钙盐，否则培养物在氯化钠浓度大于0.3m时不会生长。该浓度的Ca²⁺的加入将耐受性延长至0.5m氯化钠，直至生长停止。将光强度从1.2增加到9.4mw/cm²可提高0.10至0.45m氯化钠中培养物的生长速率。在14mw/cm²时，与未添加Ca²⁺的对照相比，添加Ca²⁺降低了0.3m氯化钠中培养物的生长速率。通过添加10mm CaSO₄并将光强度维持在9.4mw/cm²，可实现氯化钠培养基中培养物的最大生长速率。该生物体的最大生长速率为对照培养物在2.7mw/cm²时达到的9.6次/天。在0.3m氯化钠中，在2.7mw/cm²时生长速率为4.3次/天，添加10mm CaSO₄且光强度为9.4mw/cm²时生长速率为8.2次/天。将光强度从2.7增加到9.4再增加到14mw/cm²，可降低未添加Ca²⁺的0.3m氯化钠培养基中培养细胞的细胞内Na⁺，并增加添加和未添加Ca²⁺的0.3m氯化钠培养基中培养细胞的Cl⁻摄取。对于在14mw/cm²的0.3m氯化钠培养基中培养的细胞，添加Ca²⁺时细胞内Na⁺为0.68meq/g干重，未添加Ca²⁺时为0.81meq/g干重。在2.7mw/cm²添加Ca²⁺可将细胞内Na⁺降低至相似值。据推测，添加Ca²⁺降低了主动排出Na⁺的能量需求，从而使更多能量可用于细胞生长，导致生长速率增加。O₂释放和CO₂固定研究表明，光合能量增加，可能是由伴随Cl⁻内流的高质子梯度驱动且与CO₂固定解偶联，可用于维持细胞完整性和主动控制细胞内离子比率。对于在0.3m氯化钠培养基中培养的细胞（分别添加和未添加Ca²⁺），O₂释放能力在12和29mw/cm²时被破坏。对照培养物在光强度高达115mw/cm²时继续产生O₂。
