Photoperiodic Time Measurement and Effects of Temperature on Flowering in Chenopodium rubrum L

Abstract

The critical dark period length (c. 8 h darkness) required for induction of flowering of C. rubrum is insensitive to temperature (Q₁₀ c. 1.0) over the temperature range 10-25°C. However, the period of a rhythm controlling floral induction is shown to be temperature sensitive (Q₁₀ c. 1.4) over the temperature range 9-22°C. The discrepancy in temperature dependence of these two parameters of photoperiodic time-measurement could reflect differences in their rates of adjustment after a temperature shift. By contrast, at least two other species (Pharbitis nil and Hyoscyamus niger) show marked temperature sensitivity of their critical daylength. Thus, there may be more than one time- keeper in the photoperiodic control of flowering.