| Popis: |
Xanthium pennsylvanicum is induced to flower by exposure to a single uninterrupted dark period equal to or exceeding some minimum duration (ca. 9 hours). A system of stages of floral bud development is described, which gives a quantitative measurement of the degree of induction caused by various treatments. A number of factors which may affect the degree of induction are investigated, and it is concluded that age of the leaf and light intensity before and after induction strongly influence the effects of a given inductive dark period, while other factors are less important in this respect. Methods in the use of auxin are also described. Auxin is shown to inhibit induction in the leaf, but to promote floral bud development after induction is complete. Applied auxin will replace a requirement for the presence of active buds after and just before induction. The induced state is discussed, and it is proposed that this condition consists of a given concentration of florigen in the plant which is maintained at the level brought about by the act of induction. Concentration curves indicate that auxin acts in floral inhibition such as it does in other auxin-induced phenomena. Applied auxin has little effect upon the critical night length, but inhibits the rate of florigen synthesis which follows. Auxin is most effective when applied two to three hours after the beginning of the dark period, and its effectiveness decreases up until translocation of florigen out of the leaf is complete. Light interruption of the dark period is most effective after 8 hours. Light interruption and auxin are additive in their inhibitory effect. It is suggested that the act of induction consists of at least three phases: transformation of photo-receptor pigment, preparatory reaction, and hormone synthesis. A possible mechanism of auxin action through destruction of florigen is discussed. |
