Abstract
The effects of DIF (difference between day and night temperature), TD (short time temperature drop) and TR (short time temperature rising) on the growth of Delphinium grandiflorum L. cv. ‘Blue Mirror’ were investigated. Minus DIF (15°C and 25°C during the light and dark period, respectively) decreased the plant height by 42% to 49% compared to that of plants treated with plus DIF (25°C and 15°C during the light and dark period, respectively). TD down to 10°C for 4 hours started 2 hours before the end of the dark, did not influence the plant height. On the other hand, TR up to 30°C for 4 hours at the beginning of the dark period, decreased the height by 22% to 33% compared to that of +DIF. Both length and width of stem pith cells in the plants treated with −DIF, were decreased by about 20% compared to those of +DIF. Plants −DIF showed a decrease in the relative number of pith cells in the vertical direction by 26% compared to that of plants +DIF, although the number in the horizontal direction were decreased by only 5%. Endogenous gibberellins, GA9 and GA24, were identified in the shoot of D. grandiflorum. The concentration of GA24 was lower in −DIF than in +DIF, indicating that DIF regulated the stem elongation through biosynthesis of gibberellin.
