Relationship between Leaf Water Status and Endogenous Ethylene in Detached Leaves.

The pattern of changes in the internal concentration of ethylene in response to water stress was investigated in species with leaves that do abscise and leaves that do not abscise. When leaves which abscise were detached and exposed to dry air for up to 6 hours, a continuous increase of internal ethylene was observed. In water-stressed leaves which do not abscise only a transient rise in ethylene occurred. The peak, which was attained after 30 to 120 minutes, depending on the species studied, was followed by a sharp decline to the initial level. The principal site of ethylene production in response to a short period of water stress was in the blades rather than the petioles in both types of leaves. The internal ethylene level in leaves was reduced by pretreatment with the ethoxy analog of rhizobitoxine (an inhibitor of ethylene biosynthesis) or by maintaining the leaves under subatmospheric pressure. The results obtained by these methods showed that ethylene was not involved in the mechanism of stomatal movement in either turgid or in stressed leaves. Also, the increase in leaf abscisic acid content and the depletion of gibberellins induced by water stress were not related to the internal concentration of ethylene in the detached leaf. The different patterns of drought-induced ethylene production observed in the blades of leaves which exhibit abscission compared with those which do not exhibit abscission may indicate the involvement of ethylene in a primary event in the process of leaf abscission induced by water stress.