41.1 The environment influences reproduction.
Plants Undergo Metamorphosis
• Plants go through developmental changes leading to maturity by adding on structures to existing structures with their meristems. (p. 832)
• Phase changes allow plants to obtain competence to respond to external or internal signals triggering flower formation. (p. 832)
• Fully mature plants may still require specific environmental cues in order to flower. (p. 833)
Pathways Leading to Flower Production
• Three genetically regulated flowering pathways have been identified: a light-dependent pathway, a temperature-dependent pathway, and the autonomous pathway. (p. 834)
• Flowering responses to day length can fall into several basic categories, including short-day plants, long-day plants, and day-neutral plants. (pp. 834-835)
• Vernalization, a chilling period, may be necessary for certain seeds or developing plants. (p. 836)
• In some plants, flowering is independent of environmental cues, and at some point in development, shoots become determined to flower. (p. 836)
Identity Genes and the Formation of Floral Meristems and Floral Organs
• The ABC model explains how three classes of floral organ identity genes could specify four distinct organ types. (p. 838)
41.2 Flowers are highly evolved for reproduction.
Evolution of the Flower
• Successful pollination in many angiosperms depends on regular attraction of pollinators, thus floral morphology has coevolved with pollinators. (p. 840)
• The trend in floral evolution has been toward four distinct whorls; a complete flower contains all four whorls, and an incomplete flower lacks one or more whorls. (p. 840)
• The wide diversity of modern flowering plants has been driven by two trends: grouping or fusing of separate floral parts, and loss or reduction of floral parts. (pp. 841)
• Artificial selection has had a large impact on flower morphology. (p. 841)
• Primitive flowers are often radially symmetrical, while advanced flowers tend to be bilaterally symmetrical. (p. 841)
Formation of Angiosperm Gametes
• Reproductive success depends on the union of male and female gametes. (p. 842)
• Angiosperm reproductive organs differ from those of animals in that angiosperm male and female structures usually occur in the same individual flower, and angiosperm reproductive structures are not permanent parts of adult individuals. (p. 842)
Pollination
• Pollination occurs when pollen is placed on the stigma. (p. 844)
• Early seed plants were passively pollinated by the wind, but animal pollinators have also played an important role in angiosperm evolution. (p. 844)
• Animal pollinators include bees and other insects, birds, bats, and small rodents, as well as many others. (pp. 844-845)
Self-Pollination
• Self-pollination of angiosperms occurs frequently due to the ecological advantage of independence from a pollinator, and self-pollination produces uniform progeny that may be advantageous in some habitats. (p. 846)
• Outcrossing promotes genetic diversity and may be promoted by several strategies, including physical or temporal separation of stamens and pistils. (pp. 846-847)
Fertilization
• Double fertilization in angiosperms uses two sperm cells; one fertilizes an egg and the other helps form endosperm to nourish the embryo. (p. 848)
41.3 Many plants can clone themselves by asexual reproduction.
Asexual Reproduction
• Asexual reproduction is used to produce individuals genetically identical to the parent. (p. 849)
• Vegetative reproduction can be accomplished via runners, rhizomes, suckers, and adventitious plantlets. (p. 849)
Plant Tissue Culture
• Whole plants can be cloned by regenerating plant cells or tissues on nutrient medium. (p. 850)
41.4 How long do plants and plant organs live?
The Life Span of Plants
• Life span may or may not correlate with reproductive strategy. (p. 851)
• Annual plants grow, flower, form fruits and seeds, and then die, all within one growing season, while biennial plants take two years to complete their life cycle, and perennial plants continue to grow year after year. (p. 851)
• Abscission is the process by which leaves or petals are shed, and is advantageous in that a plant can shed its nutrient sinks. (p. 852)