Bi-directional inflorescence development in Arabidopsis thaliana: Acropetal initiation of flowers and basipetal initiation of paraclades

Abstract

In this study we investigated Arabidopsis thaliana (L.) Heynh. inflorescence development by characterizing morphological changes at the shoot apex during the transition to flowering. Sixteen-hour photoperiods were used to synchronously induce flowering in vegetative plants grown for 30 d in non-inductive 8-h photoperiods. During the first inductive cycle, the shoot apical meristem ceased producing leaf primordia and began to produce flower primordia. The differentiation of paraclades (axillary flowering shoots), however, did not occur until after the initiation of multiple flower primordia from the shoot apical meristem. Paraclades were produced by the basipetal activation of buds from the axils of leaf primordia which had been initiated prior to photoperiodic induction. Concurrent with the activation of paraclades was the partial suppression of paraclade-associated leaf primordia, which became bract leaves. The suppression of bract-leaf primordia and the abrupt initiation of flower primordia during the first inductive photoperiod is indicative of a single phase change during the transition to flowering in photoperiodically induced Arabidopsis. Morphogenetic changes characteristic of the transition to flowering in plants grown continuously in 16-h photoperiods were qualitatively equivalent to the changes observed in plants which were photoperiodically induced after 30 d. These results suggest that Arabidopsis has only two phases of development, a vegetative phase and a reproductive phase; and that the production of flower primordia, the differentiation of paraclades from the axils of pre-existing leaf primordia and the elongation of internodes all occur during the reproductive phase.

FLD interacts with genes that affect different developmental phase transitions to regulate Arabidopsis shoot development

“…This reversion strongly suggests a specific defect in the rosette-to-inflorescence transition in fld-2 mutants. It has been suggested that the early inflorescence phase is the result of the inhibition of vegetative leaf development in wild-type Arabidopsis (Hempel and Feldman, 1994). Therefore, the FLD gene may function as an inhibitory factor to reduce the formation of the vegetative shoot and promote the production of the inflorescence shoot by diminishing COPS activity (Figure 4).…”

Photo and hormonal control of meristem identity in the Arabidopsis flower mutants apetala2 and apetala1.

“…In addition to its functions in the control of floral organ identity, AP2 has also been shown to control the establishment of flower meristem identity, in part through its interaction with the floral meristem identity gene AP7 (Irish and Sussex, 1990;Bowman et al, 1993;Shannon and Meeks-Wagner, 1993). Strong apl mutants produce highly branched, inflorescence-like flowers that are characterized by the lack of petals, by the replacement of sepals with bractlike leaves, and by the production of ectopic secondary flowers in the axils of the first-whorl leaves (Irish and Sussex, 1990;Bowman et al, 1993;Schultz and Haughn, 1993).…”

“…Strong apl mutants produce highly branched, inflorescence-like flowers that are characterized by the lack of petals, by the replacement of sepals with bractlike leaves, and by the production of ectopic secondary flowers in the axils of the first-whorl leaves (Irish and Sussex, 1990;Bowman et al, 1993;Schultz and Haughn, 1993). These ectopic secondary or axillary flowers may in turn produce tertiary axillary flowers.…”

“…These ectopic secondary or axillary flowers may in turn produce tertiary axillary flowers. By contrast, apl-7 ap2-7 double mutants produce flowers that are more indeterminate and inflorescence-like than either single mutant alone (Irish and Sussex, 1990;Bowman et al, 1993;Schultz and Haughn, 1993;Shannon and Meeks-Wagner, 1993). …”

“…apl-7 is among the best studied of the apl mutants and is presumed to be a null allele (Irish and Sussex, 1990;Mande1 et al, 1992;Bowman et al, 1993). As shown in Figure 3A, LD-grown ap7-7 flowers are characterized by the absence of petals and the production of axillary flowers.…”