Petiole growth in Ranunculus sceleratus L.: ethylene synthesis and submergence [Semi-aquatic plants]

Petioles of the celery-leaved buttercup (Ranunculus sceleratus L.) elongate in response to treatment with ethylene in air when the leaf blades are attached. An enhanced rate of elongation growth also occurs when the leaves are submerged. Submergence causes an increase in extractable ethylene gas within the tissues, and these levels appear to approach those required to saturate the ethylene-promoted elongation growth response. Coincident with a rise in ethylene in the tissues is a dramatic increase in the level of I-aminocyclopropane-1-carboxylic acid (ACC), the precursor of ethylene. Both the petiole and leaf blade tissues have a similar capacity to evolve ethylene in the presence of added ACC. However, in air the leaf blade evolves more ethylene from endogenous resources than the petiole. The simultaneous increases in ethylene and ACC levels in submerged tissues are considered in terms of the low diffusivity of ethylene in water, the ‘autocatalytic’ effect of ethylene on ethylene biosynthesis and the rôle of both carbon dioxide and oxygen fluxes in ethylene metabolism of submerged tissues.