Apical dominance in the rhizome of Agropyron repens: the influence of humidity and light on the regenerative growth of isolated rhizomes

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Abstract
The influence of humidity and light on the regenerative growth of isolated 5-node segments from rhizomes of A. repens was investigated under controlled conditions. When the rhizomes were incubated in the dark at 20 .+-. 1.degree. C, shoot growth at the apical node was significantly reduced by each 0.5% reduction in relative humidity between 100 and 98.5%, and at 98.0% growth at all nodes was completely inhibited. The restriction of these effects to the apical end of the rhizome (nodes 1 and 2) was attributed to their interaction with the basipetal gradient of decreasing N concentration, previously identified as one of the causal factors in the polarity of bud activity. Bud inhibition at a relative humidity of 98% was eliminated by supplying water through the basal end of the rhizome. This treatment released the buds from the inhibition induced by the exposure of the rhizomes to light. Since the uptake of water by the rhizomes was also greater in the light than in the dark it was postulated that the light-induced inhibition of bud growth was due to a reduction in rhizome water potential, mediated by an increase in the rate of transpiration.