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Articles

Effect of Photoperiod on the Levels of Endogenous Gibberellins in Spinach as Measured by Combined Gas Chromatography-selected Ion Current Monitoring ¹

MSU-DOE Plant Research Laboratory, Michigan State University, East Lansing, Michigan 48824

The changes in the levels of five endogenous gibberellins (GAs) in spinach in relation to photoperiodic treatment have been examined by combined gas chromatography-selected ion current monitoring. Long-day treatment caused a 5-fold decline in the level of GA₁₉ while the levels of GA₂₀ and GA₂₉ increased dramatically during the same period. In absolute terms, the level of GA₂₀ increased from 0.8 microgram per 100 grams dry weight in short days to 5.5 micrograms per 100 grams dry weight after 14 long days. The levels of GA₁₇ and GA₄₄ did not change significantly with long-day treatment. These results are consistent with the hypothesis that GA₁₉ is converted to GA₂₀ and that this conversion is under photoperiodic control. Since stem growth in spinach is correlated with an increase in the level of GA₂₀, one major aspect of photoperiodic control of stem growth might be the availability of GA₂₀ through regulation of the conversion of GA₁₉ to GA₂₀.

¹ This work was supported by the United States Department of Energy Contract EY-76-C-02-1338.

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