Gibberellin Metabolism during Stem Elongation Stimulated by High Temperature in Lettuce

High temperatures induce bolting in lettuce. Gibberellins (GAs) play an important role in the bolting of several plant species, including lettuce. To reveal the role of GAs in this process, GA metabolic genes and endogenous GAs in early- and late-bolting cultivars were examined. Quantitative reverse-transcription polymerase chain reaction indicated that LsGA3ox1, a GA 3-oxidase gene that metabolizes GA(20) to GA(1), was significantly up-regulated by higher temperatures compared to lower temperatures in lettuce cultivars. Quantification of GA by liquid chromatographymass spectrometry/mass spectrometry showed increased GA(1) content in lettuce at higher temperatures. The application of prohexadione-calcium to inhibit GA 3-oxidase expression reduced the stem length of lettuce grown at higher temperatures. Levels of LsGA3ox1 expression and GA(1) content in a late-bolting cultivar were lower than those in an early-bolting cultivar. Our results suggest that LsGA3ox1 is a candidate for the gene responsible for increased GA(1), but the mechanism(s) of GA metabolism and/or action may differ among cultivars with different bolting characteristics.