Effects of Kinetin on Tiller Bud Elongation in Wheat (Triticum aestivum L.)

Experiments are described in which at four stages of development main tillers of wheat (Triticum aestivum L.) were isolated and inserted in test-tubes containing distilled water or kinetin. Leaves and leaf sheaths were split off to expose a lateral bud approximately 3 mm long whose growth was measured during a period of 8 days. Kinetin at 6 ppm promoted bud elongation and dry-weight gain at all stages of development and in different light intensities and photoperiods. Reducing assimilate supply either by partial defoliation of the main tiller or treatment with DCMU inhibited bud growth during the early part of development, an effect which was relieved by kinetin. TIBA applied to prevent auxin transport increased bud growth at the first two but not later stages of development. Kinetin also inhibited nodal root growth consistently. At least two phases of bud control in grasses have to be considered, the first being the imposition of apical dominance after initiation of floral organs and stem elongation, the second being the release of buds from inhibition around ear emergence. Imposition of bud inhibition appears to be a function of auxin and assimilate supply, and at this stage the promoting effects of kinetin may be through its action of mobilizing flow of assimilates. The release of buds at a later stage is apparently not associated with auxin, and kinetin may no longer be concerned with assimilate flow but rather with overcoming an inhibitory effect on bud growth emanating from the leaves.