Development of Male and Female Gametophyte & Pollination
Embryological characters during microsporogenesis, megasporogenesis, and the development of male and female gametophytes in Eustoma grandiflorum were observed by microscopy. The results are as follows. 1. The formation of anther walls was of the dicotyledonous type. The tapetum was of the heteromorphic and glandular type. Tapetal cells on the connective side elongated radially. 2. Cytokinesis in microsporocyte meiosis was of the simultaneous type and microspore tetrads were tetrahedral. 3. Mature pollen grains were 2-celled and had 3 germ furrows. 4. The ovary was bicarpellary syncarpous and unilocular, having parietal placentas. Ovules were numerous and anatropous. 5. The archespore under the nucellar epidermis directly developed a megaspore mother cell, which in turn underwent meiotic division to form 4 megaspores arranged in a line or T-shape. The chalazal megaspore was observed to be functional. 6. The formation of the embryo sac was of the polygonum type. Before fertilization, the 2 polar nuclei fused into a secondary nucleus. The mature embryo sac was made up of 7 cells. 7. It was found at a very low rate that there were 2 megasporocytes or 2 embryo sacs in an ovule.
Gametophyte , phase of plant life cycles in which the gametes, i.e., egg and sperm, are produced. The gametophyte is haploid, that is, each cell contains a single complete set of chromosomes, and arises from the germination of a haploid spore. In many lower plants, the gametophyte phase is the dominant plant form; for example, the familiar mosses are the gametophyte form of the plants. The alternate phase of the plant life cycle is the sporophyte, the diploid plant form, with each cell containing two complete sets of chromosomes. For example, in mosses the sporophyte is a capsule atop a slender stalk that grows out of the top of the gametophyte. The sporophyte develops from the union of two gametes, such as an egg fertilized by a sperm; in turn, the sporophyte forms spores that develop into gametophytes. The alternation between haploid gametophyte and diploid sporophyte phases, known as alternation of generations, occurs in all multicellular plants. As plants advanced in evolutionary development, the sporophyte became the increasingly dominant plant form and the gametophyte form has been correspondingly reduced. In contrast to mosses, for example, in the advanced angiosperms the male and female gametophytes are reduced to three-celled and seven-celled structures, respectively, found within the reproductive organs of the familiar flowering plant (the sporophyte).
Pollination is an important step in the reproduction of seed plants: the transfer of pollen grains (containing the male gametes) to the plant carpel, the structure that contains the ovule (female gamete). The receptive part of the carpel is called a stigma in the flowers of angiosperms and a micropyle in gymnosperms. The study of pollination brings together many disciplines, such as botany, horticulture, entomology and ecology. Pollination is important in horticulture because most plant fruits will not develop if the ovules are not fertilized. The pollination process as interaction between flower and vector was first addressed in the 18th century by Christian Konrad Sprengel.
The process of pollination requires pollinators: agents that carry or move the pollen grains from the another to the receptive part of the carpel. The various flower traits that attract different pollinators are known as pollination syndromes. Methods of pollination, with common pollinators or plants, are Honey bee, pollinating.
Biotic pollination occurs when pollination is mediated by an organism, termed a pollinator. Entomophily, pollination by insects, often occurs on plants that have developed blue petals and a strong scent to attract insects such as, bees, wasps and occasionally ants (Hymenoptera), beetles (Coleptera), moths and butterflies (Lepidoptera) and flies (Diptera). In Zoophily, pollination is done by vertebrates such as birds and bats, particularly, hummingbirds, sunbirds, spiderhunters, honeyeaters and fruit Bats. Plants adapted to this strategy tend to develop red petals to attract birds and rarely develop a scent because few birds have a sense of smell.
Abiotic pollination occurs when pollination is mediated without the involvement of other organisms. For example, anemophily is pollination by wind. This form of pollination is very common in grasses, most conifers, and many deciduous trees. Hydrophily is pollination by water and occurs in aquatic plants which release their seeds directly into the surrounding water. About 80% of all plant pollination is biotic. Of the 20% of abiotically pollinated species, 98% is by wind and 2% by water.
An Andrena bee collects pollen among the stamens of a rose. The female carpel structure appears rough and globular to the left. The bee's stash of pollen is on its hind leg.
Pollination management is a branch of agriculture that seeks to protect and enhance present pollinators and often involves the culture and addition of pollinators in monoculture situations, such as commercial fruit orchards. The largest managed pollination event in the world is in Californian almond orchards, where nearly half (about one million hives) of the US honey bees are trucked to the almond orchards each spring. New York's apple crop requires about 30,000 hives; Maine's blueberry crop uses about 50,000 hives each year.
Bees are also brought to commercial plantings of cucumbers, squash, melons, strawberries and many other crops. Honey bees are not the only managed pollinators: other species of bees are also raised as pollinators. The alfaltfa leafcutter bee is an important pollinator for alfalfa seed in western United States and Canada. Bumblebees are increasingly raised and used extensively for greenhouse tomatoes and other crops.
Well-pollinated blackberry blossom begins to develop fruit. Each incipient drupelet has its own stigma and good pollination requires the delivery of many grains of pollen to the flower so that all drupelets develop.
The ecological and financial importance of natural pollination by insects to agricultural crops, improving their quality and quantity, becomes more and more appreciated and has given rise to new financial opportunities. The vicinity of a forest or wild grasslands with native pollinators near agricultural crops, such as apples, almonds or coffee can improve their yield by about 20%. The benefits of native pollinators may result in forest owners demanding payment for their contribution in the improved crop results - a simple example of the economic value of ecological services.
The American Institute of Biological Sciences reports that native insect pollination saves the United States agricultural economy nearly an estimated $3.1 billion annually through natural crop production.
Pollination of food crops has become an environmental issue, due to two trends. The trend to monoculture means that greater concentrations of pollinators are needed at bloom time than ever before, yet the area is forage poor or even deadly to bees for the rest of the season. The other trend is the decline of pollinator populations, due to pesticide misuse and overuse, new diseases and parasites of bees, clearcut logging, decline of beekeeping, suburban development, removal of hedges and other habitat from farms, and public paranoia about bees. Widespread aerial spraying for mosquitoes due to West Nile fears is causing an acceleration of the loss of pollinators.
The US solution to the pollinator shortage, so far, has been for commercial beekeepers to become pollination contractors and to migrate. Just as the combine harvesters follow the wheat harvest from Texas to Manitoba, beekeepers follow the bloom from south to north, to provide pollination for many different crops.