Effect of potassium nutrition on some enzymes from ripening Lycopersicon esculentum fruit

The maximum respiration rate of tomato fruit during the climacteric period was markedly increased when the plants were grown under potassium-deficient conditions. Whereas potassium deficiency had no effect on cytoplasmic glutamate-oxoloacetate transaminase, there was a significant increase in the activity of this enzyme from mitochondria once the fruit began to change colour. Malate dehydrogenase was reduced in activity by potassium deficiency. It is suggested that the augmented mitochondrial transiminase levels, coupled with reduced malate dehydrogenase activity in low potassium fruit, result in reduced levels of oxaloacetic acid which is a potent inhibitor of Krebs cycle oxidations, thus leading to higher respiration rates for the intact fruit.