Fig. 2.

frq⁺ strains are entrained, and frq⁹ strains are driven, by temperature cycles. (A) Densitometric tracings of the conidial banding rhythm entrained to 22°C/27°C temperature cycles of varying period length (indicated at left). Shading is as in Fig. 1; middle lines report average (n ≥ 6 race tubes) pixel density, and shading above and below this line marks ± 1 SD. The widths of the cool and warm periods were drawn to scale because the growth rate is higher at the higher temperature. The end of the third warm period in each tube has been aligned as indicated by the vertical arrow, and a line was drawn through the third (and in frq⁺ fourth) peaks to highlight the trends in phase. This line is sloped in WT (Left) showing the systematic change in phase as a function of T consistent with entrainment, but the line is vertical in the frq-null strain (Right). Similar results were obtained in all three laboratories; plotted data are from one laboratory. (B) The phase of the rhythm peak under different period length (T) cycles was measured as the average number of hours the peaks occurred after (-) or before (+) the cool (22°C) to warm (27°C) (Upper) or warm to cool (Lower) transitions for frq⁹ (○) and frq⁺ (•). When plotting the phase relative to the warm to cool transition, the frq⁺ peak cannot always be unambiguously plotted as occurring before or after the transition. Thus, we plotted the results as delays (negative values) as well as advances (positive values). This plot represents all data collected independently in three different laboratories. Each data point is an average phase value from at least three cycles per race tube from n ≥ 6 race tubes ± 1 SD. To test how well entrainment period length could predict phase, we performed a linear regression analysis and found a highly significant linear relationship (P < 0.001) between phase and T in the frq⁺ strain. However, in frq⁹ the relationship was not significant (P > 0.05), indicating that this strain is not entrained. (C) Densitometric scans of frq⁺ (Left) and frq⁹ (Right) strains under cycles of 9 h/9 h (Top), 12 h/12 h (Middle), and 15 h/15 h (Bottom) at 22°C and 27°C. After the fourth full temperature cycle (first two cycles not shown), the temperature was held at 22°C for another half-cycle before resuming regular cycling. In frq⁺, the oscillation continues, whereas in frq⁹, cycling ceases until the temperature rises again, consistent with the rhythm being driven. Data are from one laboratory, n = 6 race tubes ± 1 SD; see also Fig. 5, which is published as supporting information on the PNAS web site.