The gynoecium is the female reproductive structure of flowering plants. Here we present a description of the Arabidopsis thaliana gynoecium at anthesis. The cylindrical organ can be broken down into three longitudinal regions arranged in an apical-basal order: stigma, style, and ovary. Each region can be distinguished histologically and morphologically. The transmitting (pollination) tract is axially positioned along the center of the gynoecium and spans stigma, style and ovary. Histochemistry, scanning electron microscopy and a style-specific reporter gene are used to compare the wild-type pattern of gynoecium cell types and regions, with patterns formed in gynoecia of individuals homozygous for a series of allelic mutations at the ETTIN locus. ettin gynoecia show morphological and histological alterations that appear to result from the merging of apical and basal regions and the development of abaxial into adaxial tissues. These developmental abnormalities result in a reduction of the ovary region, an expansion of the stylar and stigmatic regions, and the abaxial (outward) proliferation of transmitting tract tissue. The alterations in the mutants can be interpreted as resulting from misspecifications of position along the longitudinal and transverse axes during gynoecium development. The results suggest that early patterning events underlie wild-type gynoecium development, and that ETT functions during this early programming.

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