Apical dominance in the rhizome of Agropyron repens. Evidence of competition for carbohydrate as a factor in the mechanism of inhibition

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Abstract
When plants of Agropyron repens L. Beauv. are grown at a high nitrogen level (210 p.p.m. N) apical dominance in the rhizome is sufficiently reduced to permit the continued growth of the lateral buds. If, however, the rhizome is isolated from the parent shoot the dominance of the apex is markedly increased and lateral bud growth is strongly inhibited.Experiments with these isolated, high-nitrogen rhizomes showed that apical dominance could be significantly reduced either by increasing the length of the rhizome or by retarding the growth of the rhizome apex by exposing it to light. The growth potential of the lateral buds declined rapidly as the duration of their attachment to the rhizome apex was increased. This effect was associated with the translocation of carbohydrate to the rhizome apex and could be overcome by providing the isolated buds with a 2% sucrose solution. When buds were isolated from the rhizome apex before their growth potential was exhausted a marked increase in their carbohydrate content was apparent after 48 h. This increase was associated with their resumption of growth. Buds still attached to the apex could be released from inhibition by supplying sucrose solutions to the cut end of the rhizome.The results suggest that, under the experimental conditions, apical dominance was due primarily to competition for a limited carbohydrate supply.

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