The transition to flowering in Arabidopsis.

Given the sessile life-style of plants, reproductive success depends on the correct timing of the transition from vegetative to reproductive development. Plants need to be able to recognize the most favorable environmental conditions in order to successfully complete their reproductive development (Murfet 1977). Light intensity, photoperiod, and temperature are environmental variables that change in a largely predictable pattern throughout the year, and different light conditions and temperatures induce flowering in a wide range of plant species (Evans 1969; Bernier et al. 1981; Halevy 1985). Consequently, the flowering process involves many steps, starting from perception of environmental conditions and finishing with the differentiation of three-dimensional structures, the flower primordia at the meristem (Zeevaart 1976). Depending on their requirement for specific environmental conditions to flower, plant species can be considered as (1) autonomous, when apical meristems acquire competence and proceed from the vegetative to the reproductive program independently of environmental conditions; (2) obligate, when the transition between the vegetative and reproductive developmental programs requires specific environmental conditions to proceed; or (3) facultative, when the transition between developmental programs is hastened or delayed by different environmental factors, but there is no obligate requirement (Bernier 1988), as is the case for Arabidopsis (Napp-Zinn 1985). Arabidopsis has been the subject of physiological and genetic research on floral induction for several decades (Napp-Zinn 1969Napp-Zinn 1985; Redei 1970; Finkelstein et al. 1988; G.W. Haughn et al., in prep.). Because of the lack of specific requirements for floral transition, Arabidopsis has not been a preferred model for the...