AUXIN IN RELATION TO LEAF BLADE ABSCISSION

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Abstract
The auxin concn. of bean (Phaseolus vulgaris var. Black Valentine) leaves was detd. by means of the standard Avena assay. Samples were frozen and lyophilized prior to extraction. During the period of expansion, leaflet blades and leaf stalks contain high concns. of auxin. After reaching full expansion the leaflet blades maintain a lower concn. of auxin (equivalent to 3[mu]g. of indoleactetic acid per kg. fresh wt.) throughout the period of their normal functioning. During the same period the concn. in the leaf stalks is about 1/3 that in the blades. As the leaflet blades turn yellow an approach abscission the auxin concn. of the blades falls to that of the stalks. It is suggested that the auxin gradient across the abscission zone, rather than the absolute amt. of auxin in the organ subtended, is the controlling factor in abscission.
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