Search

The sex determination process in cucurbits involves the control of stamen or carpel development during the specification of male or female flowers from a bisexual floral meristem, a function coordinated by ethylene. A gain-of-function mutation in the miR164 -binding site of CpCUC2B , ortholog of the Arabidopsis transcription factor gene CUC2 , not only produced ectopic floral meristems and organs, but also suppressed the development of carpels and promoted the development of stamens. The cuc2b mutation induced the transcription of CpCUC2B in the apical shoots of plants after female flowering but repressed other CUC genes regulated by miR164 , suggesting a conserved functional redundancy of these genes in the development of squash flowers. The synergistic androecious phenotype of the double mutant between cuc2b and etr2b , an ethylene-insensitive mutation that enhances the production of male flowers, demonstrated that CpCUC2B arrests the development of carpels independently of ethylene and CpWIP1B. The transcriptional regulation of CpCUC1 , CpCUC2 , and ethylene genes in cuc2b and ethylene mutants also confirms this conclusion. However, the epistasis of cuc2b over aco1a , a mutation that suppresses stamen arrest in female flowers, and the down-regulation of CpACS27A in cuc2b female apical shoots, indicated that CpCUC2B promotes stamen development by suppressing the late ethylene production. [ABSTRACT FROM AUTHOR]

The shoot apical meristem (SAM) is a small population of stem cells that continuously generates organs and tissues. We will discuss here flower formation at the SAM, which involves a complex network of regulatory genes and signalling molecules. A major downstream target of this network is the extracellular matrix or cell wall, which is a local determinant for both growth rates and growth directions. We will discuss here a number of recent studies aimed at analysing the link between cell wall structure and molecular regulation. This has involved multidisciplinary approaches including quantitative imaging, molecular genetics, computational biology and biophysics. A scenario emerges where molecular networks impact on both cell wall anisotropy and synthesis, thus causing the rapid outgrowth of organs at specific locations. More specifically, this involves two interdependent processes: the activation of wall remodelling enzymes and changes in microtubule dynamics. [ABSTRACT FROM AUTHOR]

Arabidopsis, flower development, flower meristem, boundary formation, floral organ identity, APETALA3, SUPERMAN. [Extracted from the article]

Recent advances in confocal microscopy, coupled with the development of numerous fluorescent reporters, provide us with a powerful tool to study the development of plants. Live confocal imaging has been used extensively to further our understanding of the mechanisms underlying the formation of roots, shoots and leaves. However, it has not been widely applied to flowers, partly because of specific challenges associated with the imaging of flower buds. Here, we describe how to prepare and grow shoot apices of Arabidopsis in vitro , to perform both single-point and time-lapse imaging of live, developing flower buds with either an upright or an inverted confocal microscope. [ABSTRACT FROM AUTHOR]

Merism in flowers is the result of a combination of a whorled phyllotaxis, the proportion of relative sizes of floral organs and flower meristem, and pressures from external organs. Different forms of merism have evolved in major clades and represent key-innovations in floral evolution. The major forms of merism are trimery, characteristic for monocots and several magnoliids, and pentamery in the core eudicots. Despite a strong conservatism of merism within given taxonomic groups, there are several cases of meristic change. It is demonstrated that changes of merism are not random but follow complex developmental patterns. Two kinds of meristic change are recognized, isomerous changes affecting all organ whorls of a flower, and anisomerous changes only affecting part of the flower. Causes for meristic changes are analysed from a developmental (physico-mechanical) and genetic perspective. It is demonstrated that meristic change in the flower depends on the relative size proportion of preexisting outer whorls versus the flower meristem: a reduction of the size of outer perianth organs and valvate aestivation is correlated with an increase in merism. The loss or reduction of perianth parts induces a loss of meristic stability. Meristic increase is also preferentially linked with even numbers of organs, as a whorl may easily switch to two alternating whorls by space restrictions. An anisomerous increase starts preferentially from the gynoecium, mainly affecting the number and position of the stamens. [ABSTRACT FROM AUTHOR]

The shoot concept of the flower suggests that flowers correspond to vegetative short-shoots except the fact that their lateral appendages are floral and not vegetative leaves. However, in view of the different properties of vegetative and flower meristems, this concept should be questioned. Differential meristem activity resulting in tubes, hypanthia and inferior ovaries, continuous meristem expansion providing space for stamen fascicles and additional structures and the process of (repeated) fractionation using a given space completely, are characteristics of flower meristems hardly explainable with the shoot concept. Linking instead flower development with recent findings in molecular biology and computational modeling widens the view to the fundamental relation between growth and form. Given that the same general principles characterize plant growth at all life stages, the loss of apical growth appears to play the major role in changing geometry, space availability and genetic regulation in flower meristems. The flower, thus, turns out to be the sporangia bearing tip of a shoot. [ABSTRACT FROM AUTHOR]

Background and aims Flower meristems differ from vegetative meristems in various aspects. One characteristic is the capacity for ongoing meristem expansion providing space for new structures. Here, corona formation in four species of Passiflora is investigated to understand the spatio-temporal conditions of its formation and to clarify homology of the corona elements. Methods One bird-pollinated species with a single-rowed tubular corona (Passiflora tulae) and three insectpollinated species with three (P. standleyi Killip), four (P. foetida L. 'Sanctae Martae') and six (P. foetida L. var. hispida) ray-shaped corona rows are chosen as representative examples for the study. Flower development is documented by scanning electron microscopy. Meristem expansion is reconstructed by morphometric data and correlated with the sequential corona element formation. Key Results In all species, corona formation starts late in ontogeny after all floral organs have been initiated. It is closely correlated with meristem expansion. The rows appear with increasing space in centripetal or convergent sequence. Conclusions Based on the concept of fractionation, space induces primordia formation which is a self-regulating process filling the space completely. Correspondingly, the corona is interpreted as a structure of its own, originating from the receptacle. Considering the principle capacity of flower meristems to generate novel structures widens the view and allows new interpretations in combination with molecular, phylogenetic and morphogenetic data. [ABSTRACT FROM AUTHOR]

We analyzed cell division patterns during the differentiation of unisexual flowers of the dioecious plant Silene latifolia using in situ hybridization with histone H4 and cyclin A1 genes. The gene expression patterns indicated that the activation of cell divisions in whorls 3 and 4 was reversed in young male and female flower buds. During maturation of flower buds, a remarkable reduction in cell division activity occurred in the male gynoecium primordium and female stamen primordia. Our analyses showed that differential activation and reduction of cell division strongly correlated with sex-specific promotion and cessation in the sex differentiation of unisexual flowers. [ABSTRACT FROM AUTHOR]