Stamen and Pollen Development

Abstract

Stamens are the male sexual organs in flowers. Their function is to produce and disperse pollen, which carries the plant's sperm cells to the pistil. Mature stamens consist of a filament and an anther. They are initiated on floral meristems and form the third of four concentric organ whorls. The sterile filament provides a vascular connection and positions the anther for pollen dispersal. The anther sits at the tip of the filament and is the site of pollen production. Diploid germ‐line cells in the anther interior undergo meiosis to produce haploid microspores. These microspores, in turn, undergo one or two mitotic divisions, making pollen either bicellular or tricellular at the time of anthesis. Surrounding layers of nonsexual cells are essential for pollen development and also contribute to the external pollen coat. At anthesis, the mature anther splits open, and pollen is available for transfer to the pistil.

Key Concepts

  • A canonical flower contains four concentric organ whorls.
  • Stamens comprise the third whorl and function to produce and disperse pollen, which contains the male gametes.
  • Stamens are specified by the combined action of B‐ and C‐class floral homeotic genes in a floral meristem.
  • A mature stamen consists of a nonsexual filament and a four‐lobed anther that is the site of pollen production.
  • Positional information and cell–cell signalling are crucial for specifying the germ‐line pollen mother cells and surrounding somatic tissues.
  • Cells in the interior of the developing anther differentiate into germ‐line archesporial cells and then induce somatic fates in surrounding cells.
  • After meiosis, the germ‐line archesporial cells develop into pollen, and the surrounding somatic cells support pollen development.
  • At anthesis, the mature anther splits and desiccates to allow pollen dispersal.

Keywords: stamen; anther; pollen; development; signalling

Figure 1. Concentric whorls of floral organs. Stamens are the third whorl, situated between petals and carpels.
Figure 2. Unusual symmetry in anthers. (a) Adaxial–abaxial arrangement. The adaxial side of an organ faces the meristem, and the abaxial side faces away. (b) The four‐lobed anther arises by duplicating and rotating axes such that the typical terms are not fully descriptive (hence quotation marks). Each of the four quadrants will develop into a lobe with an internal layered structure.
Figure 3. Synopsis of pollen development. (a) Diploid pollen mother cells go through meiosis to form four haploid microspores. Initially, these are held together in a tetrad (one microspore is shown partially obscured). (b) Microspores develop following into pollen through a highly asymmetric first mitotic division to form the large vegetative cell (nucleus, yellow) and a small generative cell. In plants that shed tricellular pollen, second mitosis creates the two sperm cells. In plants that shed bicellular pollen, second mitosis occurs after pollination. In either case, the two sperm cells, which reside entirely within the vegetative cell, are found in association with the vegetative nucleus, forming the male germ unit.
Figure 4. Summary of anther germ‐line and somatic anther‐cell differentiation. Only one anther lobe is shown. Vascular and connective tissues are not shown. Left to right: L2‐derived cells in the anther interior give rise to the germ‐line and supporting cells. Germ‐line (archesporial, AR) fate is adopted by cells that are not in contact with epidermis and experience hypoxic conditions. AR cells secrete a peptide signal that induces parietal fate in the surrounding cells. The latter divide periclinally forming endothecium and a secondary parietal layer that divides again to form the middle layer and tapetum.
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How to Cite close
Muñoz‐Sanz, Juan V, and McClure, Bruce(May 2018) Stamen and Pollen Development. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0002040.pub2]