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A Florigenic Effect of Sucrose in Fuchsia hybrida Is Blocked by Gibberellin-Induced Assimilate Competition

Rod W. King and Yossie Ben-Tal
Plant Physiology
Vol. 125, No. 1, 75th Anniversary Issue (Jan., 2001), pp. 488-496
Stable URL: http://www.jstor.org/stable/4279670
Page Count: 9
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
A Florigenic Effect of Sucrose in Fuchsia hybrida Is Blocked by Gibberellin-Induced Assimilate Competition
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Abstract

The use of gas chromatography-mass spectrometry-selected ion monitoring along with a 13C internal standard has allowed sensitive measurements of the sucrose (Suc) content of individual shoot apices of Fuchsia hybrida. With intact plants, as the photosynthetic irradiance increased, so did shoot apex Suc content, reaching saturation at about 500 μmol m-2 s-1. These same plants flowered at the higher irradiances, remaining vegetative in 10-h short days at an irradiance of 230 μmol m-2 s-1. The strong correlation (r = 0.93) in these studies between flowering and shoot apex Suc content indicates a role for Suc as a stimulus to flowering in this species. However, Suc is not the long-day (LD) "florigen" of F. hybrida because 2 to 4 LD given as a 14-h low-irradiance photoperiod extension (10-15 μmol m-2 s-1) induced flowering but without increase in shoot apex Suc content. Flowering induced by either pathway, the LD- or the Suc-mediated one, was inhibited by applying gibberellin (GA) to the shoot tip. Such inhibition of flowering by GA, at least for the LD pathway, was associated with a reduced apex Suc content, enhanced elongation of subapical stem tissue, and a reduced import into the shoot apex of leaf-sourced assimilate. Thus, our findings show how GA inhibits flowering of F. hybrida and confirm the importance of nutrient diversion in regulating flowering.

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