Photoperiod is detected in the leaves. The cocklebur, drawn here, needs at least 8.5 hours of darkness in order to flower. Even if only a part of one leaf is exposed to the correct photoperiod, the entire plant will bloom (middle figure). The leaves produce a chemical signal — called florigen — that is transmitted to the apical meristems to start their conversion into floral meristems. The right-hand drawing shows that grafting a cocklebur (B) that receives the required period of darkness to one (A) that does not causes flowering in both. Evidently the florigen signal passes from B to A through their connected vascular systems. Link to a discussion of photoperiodism. The chemical nature of florigen has been sought for decades. The most recent evidence suggests that at least one component is the protein encoded by the gene FLOWERING LOCUS T (FT).
No comments:
Post a Comment