The endogenous level of GA1 is upregulated by high temperature during stem elongation in lettuce through LsGA3ox1 expression

Bolting of lettuce is promoted by high temperatures. Gibberellins (GAs) play an important role in the bolting of several plant species, and it has been reported that exogenous GAs induce bolting and early flowering in lettuce. To clarify the role of GAs in this process, we examined the expression of genes involved in GA metabolism (LsGA20ox-1 and -2, LsGA3ox-1 and -2, and LsGA2ox-1 and -2) and endogenous GAs in lettuce stems. Quantitative reverse-transcription PCR indicated that the expression of a GA 3-oxidase gene, LsGA3ox1, is significantly upregulated by high (35/25 °C) temperature compared to low (25/15 °C) temperature, whereas transcription of the GA 20-oxidase gene, which is upregulated in long-day conditions in arabidopsis and spinach during bolting, is not clearly affected. Quantification of GA by liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS) showed that high temperature also upregulates the content of GA1, a bioactive GA in lettuce. Our results suggest that LsGA3ox1 is a candidate for the gene responsible for the increase in GA1 during lettuce bolting at high temperatures.