The role of indol-3-ylacetic acid in regulation of juvenility inXanthium strumarium L.

Abstract

Cotyledons ofXanthium strumarium, organs with low sensitivity to photoperiodic treatment show a higher free indol-3-ylacetic acid level (by about 35 %) than the first pair leaves, organs with high sensitivity to photoperiodic treatment. This was seen in plants of three different age groups : A. with the first pair of leaves of 15-20 mm in length; B. with the first pair of leaves having finished their growth and C. with the third leaf of 30-40 mm in length.Changes in free IAA level during the inductive dark period were similar in both cotyledons and leaves of the first pair. The level of IAA rose in the first half of the dark period, began to decrease in the latter half, reaching nearly initial level at its end.Application of IAA (10-4 - 10-2M) to the cotyledons reduced their already low photoperiodic sensitivity resulting in inhibition of flowering (almost 70 % using 10-4M IAA).Elevated free IAA level is assumed to be one of the causal factors of low photoperiodic sensitivity of cotyledons.