Reduction of auxin transport capacity with age and internal water deficits in cotton petioles.

Auxin transport was examined in leaf petioles taken from the upper, middle, and lower leaf canopy of large cotton plants. The ability of petioles to transport auxin decreased with age (position) of the leaves. Plant water deficit reduced transport regardless of age. These correlations support the view that reduced transport capacity of petioles plays a significant role in the induction of abscission of lower or older leaves during water deficits.