Changes in Abscission Processes with Aging

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Abstract
The increasing tendency of bean leaves to absciss with age was examined, using the explant test and debladed intact petioles. With increasing leaf age there was a decline in responsiveness of the abscission processes to auxin (naphthaleneacetic acid), both in the inhibitory and in the promotive directions. In contrast, with increasing leaf age there was an increase in the promotive responses of abscission to the amino acid, [beta]-alanine. Analysis of these changes in context of the concept of 2 successive stages in the development of abscission leads to the deduction that an initial stage which is inhibitable with auxin is gradually completed with natural leaf aging, and the regulation of abscission becomes increasingly regulated by a 2nd stage which is promoted by the amino acid alanine.