Cobalt inhibition of thigmomorphogenesis in Bryonia dioica: possible role and mechanism of ethylene production

Rubbing-induced inhibition of elongation in Bryonia dioica was completely prevented by 10⁻⁷ M cobalt chloride. Cellular redistribution of peroxidases, mainly characterized by transiently enhanced membrane-binding of soluble peroxidases, occurred as an immediate consequence of rubbing and was not inhibited by Co²⁺. Ethylene synthesis and 1-aminocyclopropane-1-carboxylic acid (ACC) conversion readily increased upon rubbing and fell soon afterwards, but ACC conversion then increased again progressively. Co²⁺ did not drastically counteract these changes, except for the second rise in ACC conversion which was completely eliminated. The rubbing-induced rise in ethyiene production and ACC conversion was closely correlated to microsomal ACC conversion and peroxidase activity, but only during the first hours after rubbing. The presented approach enables us to correlate stress-induced ethylene production to membrane-binding of peroxidases. It is suggested that ACC conversion in Bryonia dioica is triggered by two different, sequentially ordered mechanisms. The difference in the effects of Co²⁺ on elongation and ethylene production is discussed with respect to the role of ethylene in thigmomorphogensis.