Whether Gametophytes are Reduced or Unreduced in Angiosperms Might Be Determined Metabolically.

In angiosperms, meiotic failure coupled with the formation of genetically unreduced gametophytes in ovules (apomeiosis) constitute major components of gametophytic apomixis. These aberrant developmental events are generally thought to be caused by mutation. However, efforts to locate the responsible mutations have failed.

Apospory and Diplospory in Diploid (Brassicaceae) May Facilitate Speciation by Recombination-Driven Apomixis-to-Sex Reversals.

Apomixis (asexual seed formation) in angiosperms occurs either sporophytically, through adventitious embryony, or gametophytically, where an unreduced female gametophyte (embryo sac) forms and produces an unreduced egg that develops into an embryo parthenogenetically. Multiple types of gametophytic apomixis occur, and these are differentiated based on where and when the unreduced gametophyte forms, a process referred to as apomeiosis. Apomeiotic gametophytes form directly from ameiotic megasporocytes, as in Antennaria-type diplospory, from unreduced spores derived from 1st division meiotic restitutions, as in Taraxacum-type diplospory, or from cells of the ovule wall, as in Hieracium-type apospory.

Did apomixis evolve from sex or was it the other way around?

In angiosperms, there are two pathways of reproduction through seeds: sexual, or amphimictic, and asexual, or apomictic. The essential feature of apomixis is that an embryo in an ovule is formed autonomously. It may form from a cell of the nucellus or integuments in an otherwise sexual ovule, a process referred to as adventitious embryony.

Taxonomy and Biogeography of Apomixis in Angiosperms and Associated Biodiversity Characteristics.

Apomixis in angiosperms is asexual reproduction from seed. Its importance to angiospermous evolution and biodiversity has been difficult to assess mainly because of insufficient taxonomic documentation. Thus, we assembled literature reporting apomixis occurrences among angiosperms and transferred the information to an internet database (http://www.

The OCL3 promoter from Sorghum bicolor directs gene expression to abscission and nutrient-transfer zones at the bases of floral organs.

Background And Aims: During seed fill in cereals, nutrients are symplasmically unloaded to vascular parenchyma in ovules, but thereafter nutrient transport is less certain. In Zea mays, two mechanisms of nutrient passage through the chalaza and nucellus have been hypothesized, apoplasmic and symplasmic. In a recent study, nutrients first passed non-selectively to the chalazal apoplasm and were then selectively absorbed by the nucellus before being released to the endosperm apoplasm.

Expression in Arabidopsis of a nucellus-specific promoter from watermelon (Citrullus lanatus).

Though many tissue-specific promoters have been identified, few have been associated specifically with the angiospermous megasporangium (nucellus). In the present study the 2000-bp regulatory region upstream to the watermelon, Citrullus lanatus (Thunb.) Matsum & Nakai, gene WM403 (GenBank accession no.

Apospory appears to accelerate onset of meiosis and sexual embryo sac formation in sorghum ovules.

Background: Genetically unreduced (2n) embryo sacs (ES) form in ovules of gametophytic apomicts, the 2n eggs of which develop into embryos parthenogenetically. In many apomicts, 2n ES form precociously during ovule development. Whether meiosis and sexual ES formation also occur precociously in facultative apomicts (capable of apomictic and sexual reproduction) has not been studied.

Diurnal O2 and carbohydrate levels in wheat kernels during embryony.

In vitro zygotic and somatic embryogenesis procedures for wheat have been improved by simulating in ovulo nutritional, hormonal and dissolved oxygen (dO2) conditions. However, diurnal fluctuations in these conditions during early embryony are not well characterized. In this study, dO2 and water-soluble carbohydrate Levels in wheat kernels were determined after 8 h of light and 8 h of dark at approximately 6, 12 and 18 day post anthesis (DPA).

Water stress, CO2 and photoperiod influence hormone levels in wheat.

'Super Dwarf' wheat (Triticum aestivum L.) plants have been grown from seed to maturity in the Mir space station where they were periodically exposed, because of microgravity and other constraints, to water deficit, waterlogging, high CO2 levels, and low light intensities. The plants produced many tillers, but none of them produced viable seed.