Flowering inPisum: the Effect of Light Quality on the GenotypeIfeSnHr

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Abstract
Far-red light, when given as a 16 h photoperiod extension, ia more effective than red light in reducing the flowering node of genotype Pisum. In contrast, when a 16 h dark period is interrupted by a 2 h light break red light is more effective than far-red light. In addition, the stimulatory effect of a red interruption is partially reversed by a subsequent period of far-red. However, a light interruption is not effective until over 12 h have elapsed since the start of the previous photoperiod, regardless of whether the photoperiod was of 4 or 8 h duration. The results suggest that there are two light-dependent reactions controlling flowering in peas, one operating through the phytochrome system with high levels of Pfr suppressing production of flower inhibitor by the sn gene and a second requiring continuous illumination with wavelengths above 700 nm. The role of time measurement in the photoperiod response in peas is suggested to be filled by the proportion of time the Sn gene is effectively producing inhibitor. The photoperiod response in peas is not independent of temperature or plant age since the activity of gene Sn is also varied by these factors.