COMPARISON OF THE OSMOTIC VOLUME CHANGES IN CHLOROPLASTS ISOLATED FROM DIFFERENT PLANTS

Chloroplasts were isolated from leaves of four plant species(spinach, New. Zealand spinach, Swiss Chard and tomato) andtheir osmotic behaviour was compared. Maximal contraction ofchloroplasts from all plant sources occurred at 0.3–0.4M sucrose. The volume of the particles at this sucrose concentrationwas also similar in all cases; 300 mm³ per 10¹⁰ chloroplasts.At higher and lower sucrose concentrations, the chloroplastsswell. The degree of swelling, especially in higher sucroseconcentrations, differed in chloroplasts from different sources.Tomato chloroplasts are most sensitive, and the spinach chloroplastsare the most resistant to all types of treatment. Tomato chloroplastsrequire rather high phosphate concentrations for good preservation. Changes in optical density at 520 mµ can be used to geta rough idea about the condition of the particles. (Received February 7, 1966; )