Ovular secretions as part of pollination mechanisms in conifers

Abstract

-Conifers have a diversity of pollination mechanisms that assist in the capture of pollen during pollination. Pollination mechanisms can be divided into a number of general types depending on whether they have an ovular secretion that interacts with the pollen. These types include mechanisms that never have a secretion, or those that have a delayed secretion, or the most common type in which a pollination drop is formed. This review outlines the evolutionary context of ovular secretions, describes the origins of these secretions within the ovule, their function in the two types of pollination mechanisms, and details the biochemical composition of these liquids. Not only do ovular secretions provide a germination medium for pollen, but they may also play a significant part in reducing pollen pollution by foreign species. pollination mechanism / conifer / ovular secretion / pollination drop Résumé -Les sécrétions ovulaires : leurs rôles dans les mécanismes de pollinisation des conifères. Les conifères possèdent divers mécanismes de pollinisation qui aident à la capture des grains de pollen lors de la pollinisation. Ces mécanismes peuvent être classés en quelques types généraux selon qu'une sécrétion ovulaire interagissant avec le pollen existe ou non. Ces différents types comprennent des mécanismes sans sécrétion, avec sécrétion retardée ou, et c'est le type le plus répandu, avec formation d'une goutte de pollinisation. Cet article décrit le contexte de ces secretions en terme d'évolution, leurs origines ovulaires, leurs fonctions dans les deux types de mécanis-mes de pollinisation, et leur composition biochimique. Les sécrétions ovulaires non seulement fournissent un milieu favorable à la germination du pollen, mais peuvent aussi diminuer de façon importante la pollution pollinique due à des pollens étrangers. mécanisme de pollinisation / conifère / sécrétion / goutte de pollinisation

The Pollination of Mid Mesozoic Seed Plants and the Early History of Long-proboscid Insects1,2,3

“…Secreted pollination fluid fills the micropylar tube, forming a bubble, or drop, at the terminus to trap ambient pollen (Chesnoy, 1993;Takaso & Owens, 1996). This is followed by fluid resorption or evaporation and withdrawal of the drop with trapped pollen to the nucellus where fertilization occurs through a pollen tube (Gelbart & von Aderkas, 2002). This condition has been demonstrated for late Paleozoic medullosan seed ferns (Rothwell, 1977) and a variety of fossil fructifications that have been described with ovules bearing relatively short, basally flaring micropyles consistent with wind pollination.…”

Zygotic embryogenesis and empty seed formation in European larch (Larix decidua Mill.)

“…The differences between the percentages of unfertilized ovules (especially between open pollination and self-pollination) might suggest the existence of some kind of a pre-zygotic incompatibility between pollen grains and the female gametophyte [9,24,36,37]. However, our results are mostly influenced by an occasional lack of pollination [31], whereas the percentage of pollinated, but unfertilized, ovules is almost constant [34].…”

The behavior of pollination drop secretion in Ginkgo biloba L.

“…The integument and megagametophyte have also been proposed as the origins of the PD. 10 Although the degeneration of the nucellus cells is consistent with PD production, the manner of degeneration differs among genera. For instance, in Cephalotaxus, 21 Cupressus, 22 and Podocarpus, 23 the breakdown products are transferred to the PD after degeneration of the nucellus cells, while only the uppermost layer of nucellus cells break down in Sequoiadendron 19 and Phyllocladus.…”

“…10 However, several hypotheses have been put forward regarding the origins of the PD. Anatomical studies suggest that the nucellus is the probable two-pronged (micropyle arms) in most conifers.…”

“…2 Furthermore, the PD can be augmented by rainwater or dew. 2,10 Ginkgo is one of the oldest lineages of gymnosperms. The group once flourished in the early Mesozoic, but its main habitat was destroyed during later glaciations, and only one species, Ginkgo biloba L. now survives in China.…”