Does Auxin Inhibit the Abscission of Coleus Leaves by Acting as a Growth Hormone?

Abstract

The hypothesis that auxin prevents abscission, in Coleus blumei, by causing growth has been confirmed in a number of different ways: (1) in the intact plant, petioles grow until just before abscission; (2) excising the blades causes uniformly fast abscission, which is correlated with uniform absence of elongation; (3) if one stimulates the debladed petioles to renewed growth by substituting IAA for the leaf‐blades, one can restore their longevity to that of the intact leaves; (4) increasing the concentration of IAA added to debladed petioles increases both the elongation and the longevity. However, the parallel between elongation and longevity was not exact: IAA concentrations giving full replacement of the blades in preventing abscission gave less than full replacement of elongation in petioles 2 and 3 and more than full replacement in petioles 5–8. Following the time‐course revealed that if an IAA‐treated debladed petiole elongates as much or more than normal during the first week after deblading, then it will have normal longevity.

Leaf Fall in Cassava

“…Jacobs (1955) showed that removing the apex delayed abscission of the remaining leaves, though the effect of the apical bud could be replaced by IAA. In normal plants the petioles of intact leaves elongate up to about 1 week before abscission, but though IAA replaced the leaf blade effect in preventing abscission, the changes in petiole length were not completely consistent with those of intact leaves (Jacobs et al, 1964). In a review of the hormonal regulation of abscission Jacobs (1968) concluded that auxin is the only one that has been shown to function in preventing leaf abscission.…”