Evolution of meiosis timing during floral development

Abstract

Meiosis divides the haploid and diploid portions of the life cycle in all sexual organisms. In angiosperms meiosis occurs during £ower development, the duration of which varies widely among species and is a¡ected by environmental conditions within species. For 36 species representing 13 angiosperm families, we determined the time at which meiosis ceased in the anthers as a fraction of the total time from £oral primordium initiation (beginning of development) to £ower opening (end). It was found that this fraction, rather than being continuously distributed among species, occurred in three discrete classes despite wide variations within and among species in absolute developmental durations. Each species was characterized by a single timing class. For all species within a given timing class, therefore, the durations before and after the end of microsporocyte meiosis existed in constant ratio. Each timing class was found in phylogenetically distant species; conversely, a plant family often contained more than one class. Timing class was not related to ploidy level, in£orescence architecture, pollination syndrome or mating system. These ¢ndings show that either the durations before and after microsporocyte meiosis are regulated by the same exogenous process, or one duration determines the other. They further imply that the underlying developmental processes have evolved in a limited number of ways among £owering plants.

Flower Development and the Evolution of Self-fertilization in Amsinckia: The Role of Heterochrony

“…Similarly, the actual time of PMC meiosis (AAFT) was later for homostyles of A. spectabilis, but did not differ among morphs of other clades. Relative meiosis time (RAFT) did not differ among morphs or clades (see also Li and Johnston 1999). These developmental differences mirror the differences in final form: most traits in the mature flower do not differ between furcata-vernicosa and douglasiana-tessellata, but do differ between these two clades and spectabilis (see Appendix C of Li and Johnston 2001).…”

“…The growth rate of a flower trait was calculated by dividing the size of the trait at flower opening by the flower developmental duration. In addition to primordium initiation and flower opening, we used meiosis termination in the anther as a developmental reference point (Li and Johnston 1999). The formation of microspore tetrads signals the end of meiosis in the pollen mother cells (microsporocytes).…”

“…Each bud on an inflorescence was numbered starting from the youngest flower primordium (zero) and ending with the newly opened flower (Li and Johnston 1999). The flower developmental duration, i.e., the days needed for a flower to develop from primordium to anthesis (opening), was obtained by multiplying the total number of buds on the inflorescence by the time separating positions (days/ position) on that inflorescence.…”

Evaluation of microsporogenesis in an interspecific Brachiaria hybrid (Poaceae) collected in distinct years

“…in a study involving 36 species representing 13 angiosperm families, Li and Johnston (1999) concluded that the floral timing varied from 5 to 34 days and detected environmental effects within species. Members of the Poaceae were not evaluated, but in the majority of species studied, the floral timing was estimated to be between 10 to 20 days.…”

PHENOMENON OF FLORAL REVERSION IN BOLTING GARLIC (Allium sativum L.)

“…TFL1, LFY, AP1), whose activity induces formation of the flower. Next, the meristem identity genes activate further genes (ABCE class of genes) involved in the socalled floral changes in organ identity [Coen and Meyerowitz 1991, Li and Johnston 1999, Pidkowich et al 1999, Hempel et al 2000, Pelaz et al 2000].…”