38.1 An Introduction to Flowering Plant Reproduction

• Asexual reproduction does not involve fertilization.

  • It results in the production of clones-genetically identical copies of the parent plant.

• Sexual reproduction is based on meiosis and fertilization.

• An individual in the diploid phase of the life cycle is called a sporophyte, while an individual in the haploid phase of the life cycle is called a gametophyte.

• It maybe recall that is a type of life cycle, called alternation of generations, has evolved independently in various protists and land plants.

• Meiosis occurs in sporophytes and results in the production of haploid spores.

• Meiosis and spore production occurs inside structures called sporangia.

• Pollination (transfer of pollen grains from an anther to a stigma) occurs, and gametophytes produce sperm (male gametes) and eggs (female gametes) by mitosis.

• Fertilization occurs when two gametes fuse to form a diploid zygote.

38.2 Reproductive Structures

• Sepals are leaflike structures that make up the outermost parts of a flower.

  • The entire group of sepals in the flower is collectively called the calyx.

• Stamens are reproductive structures that produce male gametophytes-also known as pollen grains.

• The male gametophytes, in turn, produce sperm that are eventually carried to eggs.

• The wall of a pollen grain develops a tough outer coat that includes the watertight compound called sporopollenin.

38.3 Pollination and Fertilization

• Self-fertilization, or selfing, occurs when a sperm and an egg from the same individual combine to produce offspring.

• In most cases, though, plants outcross-meaning at sperm and an egg from different individuals combine to form offspring.

  • Outcrossing is the result of cross-pollination-when pollen is carried from the anther of one individual to the stigma of a different individual.

• Pollination syndromes are suites of flower characters that are associated with certain types of pollinators.

• Germination is a resumption of growth and development.

  • This step is blocked in many self-incompatible species if the pollen came from the same plant.

• When pollen germinates, the tube cell elongates and forms a structure called a pollen tube that grows through the stigma and down the length of the style.

• The triploid nucleus resulting from this second fertilization undergoes mitosis and cytokinesis to form the endosperm (“inside-seed”) tissue.

38.4 Seeds and Fruits

• As a seed matures, the embryo and endosperm develop inside the ovule and become surrounded by a covering called a seed coat.

• As the fruit matures, the walls of the ovary thicken to form the pericarp, the part of the fruit that surrounds and protects the seed or seeds.

• Once they have dispersed from the parent plant, seeds may not germinate for a period of time.

  • This condition is referred to as dormancy.

  • Dormancy is usually a feature of seeds from species that inhabit seasonal environments, where for extended periods conditions may be too cold or dry for seedlings to thrive.

• The radicle, or embryonic root, emerges first, and it then develops into the mature root system.

  • This is important because the seedling must have a source of water in order to grow.

38.5 Embryogenesis and Vegetative Development

• Vegetative development produces the nonreproductive portions of the plant body-the roots, leaves, and stems.

• As a plant matures, some shoot meristems will produce reproductive structures, a process known as reproductive development.

• Embryogenesis is the developmental process by which a single-celled zygote becomes a multicellular embryo.

38.6 Reproductive Development

• The first hint of an answer came over 100 years ago when researchers discovered several types of homeotic mutations in flowers of popular garden plants.