| Abstract: | The effects of different ratios of red to far-red light (R/FR-ratio) and of exogenously applied growth regulators on the morphology of plants from sun and shade populations were studied. Large differences in growth form were found between populations adapted to either sun or shaded habitats. Low R/FR-ratios, simulating vegetation shade, induced a growth form similar to that of plants from the shade population. High R/FR-ratios, simulating sunlight, had the opposite effect. Most morphological differences between shade and sun populations and effects of low R/FR-ratios on growth form could be mimicked by exogenously applied gibberellin (GA3). In contrast, application of a gibberellin inhibitor (CCC) induced a growth form similar to that of the sun population and of plants grown under a high R/FR-ratio. Interactions between genetic background, the R/FR-ratio, and hormone treatment, were small and the factors exerted their action independently. The results are discussed in relation to the influence of developmental constraints on the evolvability of optimal phenotypes and the plastic responses therein. |
