Osmotic Adjustment by Intact Isolated Chloroplasts in Response to Osmotic Stress and Its Effect on Photosynthesis and Chloroplast Volume

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Abstract
Spinach leaf chloroplasts isolated in isotonic media (330 millimolar sorbitol, −1.0 megapascals osmotic potential) had optimum rates of photosynthesis when assayed at −1.0 megapascals. When chloroplasts were isolated in hypertonic media (720 millimolar sorbitol, −2.0 megapascals osmotic potential) the optimum osmotic potential for photosynthesis was shifted to −1.8 megapascals and the chloroplasts had higher rates of CO2-dependent O2 evolution than chloroplasts isolated in 330 millimolar sorbitol when both were assayed at high solute concentrations.