Table 1

Experiments to determine the time of commitment to flowering

Inductive exposure after 23 SDsNo. of primary shoot leavesNo. of plants
Experiment A
 0 LD12 (only SD8)43.6  ± 2.105
 2 LD12s38.0  ± 2.006
 3 LD12s36.0  ± 2.616
 4 LD12s34.7  ± 1.895
 5 LD12s28.2  ± 1.475
 7 LD12s28.8  ± 2.285
Experiment B
 3 LD12s33.0  ± 2.164
 4 LD12s29.5  ± 2.0611
 4 LD12s + 3 h28.3  ± 1.8611
21.0  ± 1.738
 4 LD12s + 6 h20.3  ± 1.4518
 4 LD12s + 9 h19.5  ± 1.8615
Experiment C
 3 LD12s36.1  ± 2.0215
 4 LD12s35.8  ± 3.838
26.4  ± 1.3610
 4 LD12s + 6 h26.1  ± 2.3213
 5 LD12s + continuous light22.9  ± 1.3221
 4 LD12s + continuous light22.8  ± 1.8517
  • Plants were returned to SD8 conditions at the end of each LD12 and grown until they eventually flowered. When plants commit to flowering they stop producing leaves on their primary shoots, and thus total leaf number produced under different light treatments indicates the relative time of commitment to flowering. Leaves were counted after plants had produced inflorescence stems, and all leaves were visible macroscopically. High or low numbers of leaves correspond to late or early commitment, respectively. In all experiments plants were grown for 23 days under noninductive SD8 conditions. In Experiment A, plants then were transferred to LD12 conditions to induce flowering. Commitment to flowering occurred between the fourth and fifth LD12. In Experiment B, plants that received four LD12s were given an additional 3, 6, or 9 h of light before they were returned to SD8 conditions. After an additional 6 h of light, full commitment to flowering occurred. Note that all plants in this experiment produced fewer leaves overall than in Experiments A and C, although commitment occurred at approximately the same time. In Experiment C, plants were treated similarly to those in Experiment B, but in addition plants were exposed to continuous light until bolting after either the fourth or fifth LD12. This population of plants committed slightly earlier than plants in Experiments A and B.