Fig. 5.

Short-term exposure to long days rapidly induces flowering in Arabidopsis thaliana (Columbia-0 (Col-0)), and FLOWERING LOCUS T (FT) transcript accumulation correlates with final rosette leaf number across treatments and mutant strains within the Col-0 background. (a) Seven-day-old seedlings were transferred to LD22/22°C (long days with day: night temperatures = 22°C: 22°C) and LD22/12°C for 14 d. After each LD, beginning on day 1, a subset of seedlings were transferred to short days (SD) and allowed to grow until bolts were observed (closed circles). A Hill function (dashed line) describing the final rosette leaf number (LfNmbr) at bolt as a function of days exposed to LD (days) was fitted to the flowering data: LfNmbr = {(Bmax(tc^n))/(tc^n + days^n)} + Bmin, where Bmax is highest fitted leaf number at bolt (= 52.17 leaves), Bmin is lowest fitted leaf number at bolt (= 8.23 leaves), tc is day at which transition occurs (= 4.86), n is modifier affecting abruptness of the transition (= 8.31) (P <0.0001 for fit of all parameters). (b) Number of rosette leaves added each week for Col-0 wild-type plants, co-101, ft-101, and svp-31 in LD22/22°C and LD22/12°C conditions. Black arrows indicate when transition to bolting occurred. Error bars; means ± standard deviation. Overall temperature effect (P<0.001), mean for difference between temperature treatments and 95% Confidence Interval (CI, 0.008, −0.134, 0.1497). The strains are plotted adjacent to the others for ease of comparison; however, all were planted at the same time. At time week 1, seedlings were 7 d old and had not yet been exposed to long-day temperature treatments. LMER was used to test for a delay in leaf production, followed by Satterthwaite approximation to generate P-values. Leaf numbers to the right of the arrow were excluded from the test as plants in the LD22/22°C treatment had begun to bolt and stopped rosette leaf production. Note that svp-31 plants began to bolt within the first week of treatment, so do not show the same pattern as the other strains, Landsberg erecta (Ler), and Wassilewskija-2 (Ws-2) had patterns similar to svp-31 and so are not shown. (c) Final rosette leaf number plotted against daytime FT transcript accumulation harvested from time points at zeitgeber time (ZT) 0, ZT8, and ZT16 across several photoperiod and temperature conditions, and strains within the Col-0 background (closed circles), and for Ler and Ws (open circles). Accumulated FT at time points ZT0, ZT8, and ZT16 (dawn, trough, and dusk) was found by integrating under the curve and is normalized to Col-0 harvested at ZT16 in LD22/22°C constant temperature conditions. Data is linearized by transforming as shown in inset for linear regression analysis (RMSE = 0.208 log(leaves)).