Photoreversibility of Flower Initiation.

Abstract

Action-spectrum studies have shown that such diverse light-controlled plant responses as flower initiation (1, 17, 18), internode elongation (2, 8, 19), leaf expansion (8, 19), and seed germination (4, 23) are regulated most effectively by red radiation near 6500 ?. Borthwick et al (4) recently demonstrated that the red reaction inducing the germination of lightsensitive lettuce seed could be reversed. Their studies show that far-red near 7350 ? is the region of maximum effectiveness in reversing the red reaction and thereby inhibiting seed germination. Thus, seed irradiated with red are put into a germinating condition that is nullified or reversed if a far-red irradiation immediately follows the red. This duodirectional reaction was shown to be repeatedly reversible and to be independent of temperature. This same reversible photoreaction was also established for the control of flower initiation of Xanthium (3), cuticle coloration of tomato fruits (20) and photomorphogenic effects such as leaf expansion (8, 12), hypocotyl elongation (8) and the disappearance of the plumular hook of dark-grown beans (26). The purpose of the studies reported herein was to investigate some of the details of this photoreversible reaction as it applies to the control of flower initiation.