?Expt. 7. Sexual Plant Reproduction: Testing conditions required for pollen germination and tube growth ____________________________________________________________________________ File: pollen
Modified from E. Moctezuma & others for BSCI 442 (Sze)
Get familiar with the parts of flowers: male and female organs Observe pollen germination and tube growth in real time.
Test the conditions that stimulate pollen germination and tube growth. Observe cytoplasmic streaming (due to vesicle traffic).
Flowering plants, or angiosperms, are the largest and most successful plant group in the world. From giant eucalyptus trees to minuscule duckweeds, from desert cacti to water lilies, these familiar plants dominate the world. They play a significant role in providing food and shelter for animals and other organisms. There are over 250,000 species of flowering plants and they are all vascular seed plants that have flowers and fruits. Angiosperms derive their name from the Greek words angion (vessel) and sperma (seed). The flower contains the vessel that houses the seed. It is also the organ for sexual reproduction.
A typical flower is composed of modified leaves arranged in four whorls (circles) on the end of an enlarged portion of the stem called the receptacle. The calyx is the outer (and lowest) whorl of floral parts and often functions to enclose and protect the flower bud before it opens. Individual members of the calyx, usually green, are called sepals. Moving inward, the second whorl of floral parts is the corolla. Individual members of the corolla are called petals, which are often conspicuously colored to attract insects or birds that serve as pollinators. Plants that are wind-pollinated or that self-pollinated do not have colorful petals, such as the model plant Arabidopsis.
Fig. 1. Arabidopsis plant and flower
(Taiz Fig 16.1)
Sepals and petals are considered the sterile parts of a flower because they are not directly involved in meiosis and sexual reproduction. The third whorl consists of the male portion of the flower, the stamens. Each stamen is composed of two parts, an anther and a filament. The anther is a four-chambered structure where pollen is produced. The male gametes are contained within pollen. The filament is the threadlike stalk that supports the anther. The female part of the flower contains one or more pistils (also referred to as carpels) and occupies the innermost whorl. Each pistil is composed of three parts: a stigma, the receptive tip where the pollen lands; the style, which is an elongated tubular structure through which the pollen tube grows after pollen germination; and at the base is the ovary. Arabidopsis had multiple ovules within two fused carpels (Fig. 1).
The production of flowers and seeds within fruits are two evolutionary advancements that only flowering plants possess. A number of other advancements can be summarized as part of their overall adaptability. That is, flowering plants have evolved numerous adaptations in structure and function in order to survive in the many different environments found on earth. This adaptability can be demonstrated in their form and structure, their physiology, and their biochemistry.
Alternation of Generations in Flowering Plants
Flowering plants reproduce sexually and have an alternation of generations. The life cycle of flowering plants involves the alternation of a diploid sporophyte stage and haploid gametophyte stage. The haploid gametophyte generation in flowering plants is very reduced and is enclosed within and dependent on the sporophyte. Flowering plants, like the gymnosperms, are heterosporous (produce two kinds of spores). The two types of spores are called microspores and megaspores.
Fig. 2 Life cycle of plants. Plants have an alternation of generations: the diploid spore-producing plant (sporophyte) alternates with the haploid gamete-producing plant...
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