Effect of α-Tomatine on the Integrity and Biochemical Activities of Isolated Plant Cell Organelles

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Abstract
Respiration in isolated mung bean shoot mitochondria was not affected by either of the tomatine treatments (10−3 M, pH 5, and 10−5 M, pH 8) but was reduced in the excised shoots by both treatments, although only at the higher of the two temperatures (5 °C and 25 °C). Inhibition was gradual and took at least 2 h. Tomatine treatment of excised shoots also resulted in an increased leakage of K+. PS II activity in isolated spinach leaf chloroplasts was reduced only by the high pH tomatine treatment at 25 °C. Again, about 2 h treatment was required before significant effects were observed but the alkaloid did not cause disintegration of the chloroplast as measured by pigment release. Disruption of lysosomes isolated from cauliflower inflorescence tissue and release of acid phosphatase was enhanced by tomatine. Initially only 10−5 M tomatine at pH 8 was effective but, later, effects could only be obtained with 10−3 M alkaloid at pH 5. The differential susceptibility of these organelles to tomatine is discussed in relation to membrane structure and to the mode of toxicity of the alkaloid.