The Dual Role of Auxin in Flowering.

Abstract

Some factors which affect the photoperiodic response of Xanthium are discussed. When plants are defoliated to a single leaf, the age of this leaf is critical[long dash]the most rapidly expanding leaf is most sensitive. Time of year (light intensity) is critical[long dash]in winter (low light intensity) degree of flowering is reduced. Temperature, age of plants, and a dim green light used during the dark period are less important. A system of floral stages based upon rate of development of the floral bud is described. Floral stage is proportional to time after induction and, a few days after induction, is proportional to length of the inductive dark period. Time of auxin application experiments indicate that auxin inhibits flowering if applied before translocation of the flowering stimulus is complete, and promotes rate of floral bud development if applied after this time. The promotive effect is demonstrated most readily under low light intensity. The promotive effect of applied auxin acts independently of the leaf, although the inhibitory effect occurs only in the leaf. If actively growing buds are removed during or after induction, the dormant buds, when they become active, remain vegetative. Auxin applied two or three days after induction overcomes this requirement for active buds.