Thermo- and Photoperiodicity and Involvement of Gibberellins during Day and Night Cycle on Elongation Growth of Begonia x hiemalis Fotsch

Abstract

The effects of thermo- and photoperiodicity on elongation growth and on endogenous level of gibberellins (GAs) in Begonia x hiemalis during various phases of the day-night cycle have been studied. Plant tissue was harvested during the day and night cycle after temperature and photoperiodic treatments and analyzed for endogenous GAs using combined gas chromatography and mass spectrometry. Elongation growth increased when the difference between day and night temperature (DIF = DT − NT) increased from a negative value (−9.0 and −4.5°C) to zero and with increasing photoperiod from 8 to 16 h. When applied to the youngest apical leaf, gibberellins A1, A4, and A9 increased the elongation of internodes and petioles. GA4 had a stronger effect on elongation growth than GA1 and GA9. In relative values, the effect of these GAs decreased when DIF increased from −9 to 0°C. The time of applying the GAs during a day and night cycle had no effect on the growth responses. In general, endogenous levels of GA19 and GA20 were higher under negative DIF compared with zero DIF. The level of endogenous GA1 in short day (SD)-grown plants was higher under zero DIF than under negative DIF, but this relationship did not appear in long day (LD)-grown plants. The main effects of photoperiod seem to be a higher level of GA19 and GA1 at SD compared with LD, whereas GA20 and GA9 show the opposite response to photoperiod. No significant differences in endogenous level of GA1, GA9, GA19, and GA20 were found for various time points during the diurnal day and night cycle. Endogenous GA20 was higher in petiole and leaf compared with stem, whereas there were no differences of GA1, GA9, and GA19 between plant parts. No clear relationship was found between elongation of internodes and petioles and levels of endogenous GAs.