Abstract
It is argued that modulation of the cytoplasmic Ca 2+ of plant cell protoplasts should be expected to decrease their ability to incorporate membrane material and thus to resist osmotic shock. Protoplasts from Avena sativa were incubated with ionophore A23187 under various conditions, and the extent of protoplast lysis was determined by the use of fluorescein diacetate. The amount of lysis was strongly dependent on both the extracellular Ca 2+ concentration and the extracellular pH. The influence of the ionophore concentration itself and the incubation time were also investigated. The results suggest that a certain level of intracellular Ca 2+ is important for maintaining plasma membrane integrity, even under isotonic conditions.
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