Factors Influencing Abscission.

Abstract

The time for abscission of explants is greatly influenced by the age of the leaf, and the presence of light, sugar, and auxin during the test. Sucrose was found to stimulate the abscission of explants low in endogenous substrates under conditions of darkness, and to inhibit abscission at high concentrations in all but older explant samples. Auxin (naphthaleneacetic acid) was found to promote abscission at low concentrations (e.g., 10"5 [image]) and inhibit at high concentrations (e.g., 10"3 [image]) within a wide variety of conditions and ages. The promotion effect was not obtained with young explants held in darkness, or with older explants which had a low carbohydrate reserve unless substrate was added. It is concluded that auxin generally has a two-phase action on abscission, but that its action is mediated by leaf age, light, and the supply of substrates such as sugar.