THERMOPERIODICITY AND PHOTOPERIODICITY AND INVOLVEMENT OF GIBBERELLINS DURING DAY AND NIGHT CYCLE ON ELONGATION GROWTH OF BEGONIA X HIEMALIS FOTSCH

The effects of thermo-and photoperiodicity on elongation growth and on endogenous level of gibberellins (GAs) in Begonin x hiemalis during v arious phases of the day-night cycle have been studied. Plant tissue w as harvested during the day and night cycle after temperature and phot operiodic treatments and analyzed for endogenous GAs using combined ga s chromatography and mass spectrometry. Elongation growth increased wh en the difference between day and night temperature (DIF = DT - NT) in creased from a negative value (-9.0 and -4.5 degrees C) to zero and wi th increasing photoperiod from 8 to 16 h. When applied to the youngest apical leaf, gibberellins A(1), A(4), and A(9) increased the elongati on of internodes and petioles. GA(4) had a stronger effect on elongati on growth than GA(1) and GA(9). In relative values, the effect of thes e GAs decreased when DIF increased from -9 to 0 degrees C. The time of applying the GAs during a day and night cycle had no effect on the gr owth responses. In general, endogenous levels of GA(19) and GA(20) wer e higher under negative DIF compared with zero DIF. The level of endog enous GA(1) in short day (SD)-grown plants was higher under zero DIF t han under negative DIF, but this relationship did not appear in long d ay (LD)-grown plants. The main effects of photoperiod seem to be a hig her level of GA(19) and GA(1) at SD compared with LD, whereas GA(20) a nd GA(9) show the opposite response to photoperiod, No significant dif ferences in endogenous level of GA(1), GA(9), GA(19), and GA(20) were found for various time points during the diurnal day and night cycle. Endogenous GA(20) was higher in petiole and leaf compared with stem, w hereas there were no differences of GA(1), GA(9), and GA(19) between p lant parts. No clear relationship was found between elongation of inte rnodes and petioles and levels of endogenous GAs.