Photoperiodic flower induction in <Emphasis Type="Italic">Ipomoea nil</Emphasis> is accompanied by decreasing content of gibberellins

The involvement of gibberellins (GAs) in the control of flower induction in the short-day plant Ipomoea nil has been investigated. To clarify the molecular basis of this process, we identified the full-length cDNAs of the InGA20ox3 and InGA2ox1 genes, which encode enzymes responsible for GA biosynthesis and catabolism, respectively. We studied the expression patterns of both genes and determined the tissue and cellular immunolocalisation of gibberellic acid (GA₃) in the cotyledons of 5-day-old seedlings growing under inductive and non-inductive photoperiodic conditions. In the second half of the inductive night, which is crucial for flower induction in I. nil, InGA20ox3 expression decreased, whereas InGA2ox1 mRNA accumulated, which indicates that photoperiod regulates the activity of both genes. Furthermore, these changes are correlated with GA₃ level. Thus, our results support the thesis that the proper balance between the expression of the InGA20ox3 and InGA2ox1 genes and low GA₃ content correlate with photoperiodic flower induction in I. nil.