Stamens

Abstract Stamens are the male reproductive organs of flowers. Typically, a stamen is made up of a pollen‐producing anther borne on a filament. Pollen arises in four sporogenous regions within the anther. The sporogenous cells are surrounded by nutritive support cells, the tapetum. Mature pollen is released from the anther by dehiscence of the anther wall. The developmental identity of the stamen is conferred by the combined action of MADS transcription factors. Subsequent cellular differentiation is under the control of a cascade of other transcription factor and signalling genes now being identified. Male sterility is useful in plant breeding, and may arise by loss‐of‐function of these genes, as well as by defects in mitochondria (cytoplasmic male sterility). Differences in the structure of stamens are associated with the types of pollinators involved. Stamens evolved from the microsporangia‐bearing organs of early seed plants. Key Concepts: Pollen is generated in stamens, the male reproductive organs of flowers. Pollen arises from sporogenous cells within the anthers. Sporogenous cells are surrounded by the tapetum, a nutritive layer of support cells. Stamen identity is conferred by the action of MADS transcription factors controlling B, C and SEPALLATA function. The transcription factor SPOROCYTELESS is required for generation of the sporogenous cells. Other transcription factors and signalling kinases are required for the entire developmental cascade and are now being identified. Mature pollen is released by dehiscence of the anther wall through slits called stomia. The structure of stamens in a species is closely adapted to the specific pollinators involved for that species. Pollen is also generated in nonflowering seed plants (gymnosperms and various extinct lineages), but it arises in leaf‐like organs (microsporophylls) rather than stamens.