2020 年 12 巻 p. 2-10
For developing a student laboratory exercise on flower initiation (floral development) in senior high school biology, we selected the Wisconsin Fast Plants (WFPs) which are the new varieties of rape (Brassica rapa, syn. campestris) as our experimental material. We examined the effects of temperature, day length, light intensity and the plant hormone gibberellic acid (GA3) on the flower initiation of WFPs. Under continuous light, the days required for detecting the first flower bud were dependent on the growth temperature being between 15°C and 35°C; the higher the temperature was, the faster the flower bud formation was. In the temperature range examined, the first flower bud could be detected within at least nine days (at 15°C) after sowing the seeds. Flower initiation was dependent on the day length at 15°C, but not at 25°C. At 15°C, flower buds formed nine days after sowing the seeds under continuous light, while no flower bud was detected nearly two weeks after the seeds were sown under a short-day condition (L:D = 8:16). The intensity of light in a long-day treatment (L:D = 16:8), from about 10 μmol·m-2·s-1 (ca 1,500 lux) to 100 μmol·m-2·s-1 (ca 13,000 lux) at 15°C, did not affect flower bud formation. The flower initiation in the plants treated with 0.01 μg·mℓ-1 GA3 was faster than in the untreated plants. The results obtained in the present study reveal that by using the WFPs students can get clear results on the effects of photoperiod, temperature, and the plant hormone gibberellin on the flower initiation of long-day plants within a shorter period than by using any other plant. Biology teachers possibly can organize a student laboratory on the photoperiodic response of plants referring to the present report.
