Plant Reproduction Chapter41

Plant Reproduction : Plant Reproduction Chapter 41


Environmental Influences on Reproduction : Environmental Influences on Reproduction Once plants are competent to reproduce, a combination of factors determine when a flower is produced. Plants go through developmental changes leading to reproductive maturity. phase change


Flower Initiation : Flower Initiation


Pathways to Flower Production : Pathways to Flower Production Genetically regulated flowering pathways light-dependent short-day plants long-day plants day-neutral plants temperature-dependent vernalization - period of chilling


Flowering Response to Daylength : Flowering Response to Daylength


Evolution of the Flower : Evolution of the Flower Pollen matures within the anthers and is transported to the stigma of another flower. When pollen reaches the stigma, it germinates, and a pollen tube grows down, carrying sperm nuclei to the embryo sac. seed matures within ripening fruit


Floral Evolution : Floral Evolution Characteristics A complete flower has four whorls, while an incomplete flower lacks at least one. calyx, composed of sepals, makes up outermost whorl petals collectively make up the corolla stamens collectively compose androecium stamens made up of filament and anther


Floral Evolution : Floral Evolution Gynoecium refers to the collection of female parts in a flower. single or fused carpels also referred to as simple or compound pistils ovules produced in pistil’s swollen ovary style - slender neck stigma – pollen receptive structure


Angiosperm Flower : Angiosperm Flower


Floral Evolution : Floral Evolution Trends in floral specialization separate floral parts have fused floral parts have been lost or reduced result of natural selection and artificial breeding Trends in floral symmetry many flowers of advanced groups are bilaterally symmetrical often associated with advanced pollination systems


Formation of Angiosperm Gametes : Formation of Angiosperm Gametes Plant sexual life cycles are characterized by an alternation of generations. Diploid sporophyte gives rise to haploid gametophyte generation. Male gametophytes (microgametophytes) - Pollen grains Female gametophyte (megagametophyte) - Embryo sac


Formation of Angiosperm Gametes : Formation of Angiosperm Gametes Angiosperms have separate structures for reproduction . Similar to animals, except: Male and female structures usually occur together in the same individual flower. Angiosperm reproductive structures are not permanent parts of the adult individual.


Formation of Angiosperm Gametes : Formation of Angiosperm Gametes Pollen Formation Each pollen sac contains specialized chambers enclosing microspore mother cells. Undergo meiosis to form four haploid microspores. Pollen grain shapes are specialized for specific flower species.


Formation of Angiosperm Gametes : Formation of Angiosperm Gametes Embryo Sac Megaspore mother cell found within each ovule. Undergoes meiosis to produce four haploid megaspores. Usually only one survives and the other seven are absorbed by the ovule. Remaining megaspore undergoes mitosis and produces eight haploid nuclei enclosed in an embryo sac.


Pollen Grain and Embryo Sac Formation : Pollen Grain and Embryo Sac Formation


Pollination : Pollination Pollination - Pollen is placed on the stigma. Early seed plants pollinated passively. Pollination by Animals Bees - Initially locate food sources by odor, and then orient on a flower by its shape, color, and texture. May drive coevolution.


Pollination : Pollination Other Insects Butterflies Moths Birds Many plants produce large amount of nectar to attract birds. Hummingbirds Red colors tend to attract birds, while carotenoids tend to attract insects because they are visible in the UV range.


Pollination : Pollination Other Animals Bats Rodents Monkeys Wind-Pollinated Angiosperms Typically have small, greenish, odorless flowers with reduced or absent corollas. Often grouped in large numbers and hang down in tassels.


Self-Pollination : Self-Pollination Two basic reasons for self-pollination. Ecologically advantageous as they do not need to be visited by animals, and thus do not have to expend energy producing attractants. Produces more uniform progeny than outcrossing. Well-adapted to particular habitats.


Self-Pollination : Self-Pollination Factors Promoting Outcrossing Dioecious plants produce only ovules or only pollen on a single individual. Monoecious produce both on same plant. Dichogamous - Functional stamens and pistils present on same plant, but reach maturity at different times.


Self-Pollination : Self-Pollination Self-incompatibility results when pollen and stigma recognize each other as genetically related and pollen tube growth is blocked.


Fertilization : Fertilization Double Fertilization results in two key developments: Fertilization of the egg. Formation of endosperm. Pollen grains adhere to the stigma and grow a pollen tube that pierces the style. Grows until it reaches the ovule in the ovary.


Fertilization : Fertilization Tip of pollen tube bursts and releases two sperm cells. One fertilizes the egg cell forming a zygote. The other cell fuses with two polar nuclei located at the center of the embryo sac.


Pollen Tube Formation and Fertilization : Pollen Tube Formation and Fertilization


Asexual Reproduction : Asexual Reproduction Vegetative Reproduction - New plants are cloned from adult parts. Runners Rhizomes Suckers Adventitious Plantlets Apomixis - Embryos in seeds produced asexually from the parent plant. New individuals are genetically identical to parents.


Life Span of Plants : Life Span of Plants Once established, plants live for highly variable periods of time. Life span may or may not correlate with reproductive strategy. Woody plants which have extensive secondary growth, nearly always live longer than herbaceous plants, which have limited to no secondary growth. Complicated for clonally reproducing species.


Life Span of Plants : Life Span of Plants Annual Plants Annual plants grow, flower, and form fruits and seeds within one growing season, and then die when the process is complete. Grow rapidly under favorable conditions. Developing flowers or embryos use hormones signaling nutrient reallocation.


Life Span of Plants : Life Span of Plants Biennial Plants Biennial plants have life cycles that take two years to complete. Photosynthate stored in underground storage organs during the first year. Flowering stems are produced during the second year.


Life Span of Plants : Life Span of Plants Perennial Plants Perennial plants grow year after year. Majority of vascular plants are perennial. Food is often stored in roots or underground stems which can become relatively large. Trees and shrubs generally flower repeatedly. Deciduous or Evergreen.


Life Span of Plants : Life Span of Plants Organ Abscission Abscission - Shedding of leaves or petals. Dispense with nutrient sinks. Shaded leaves, petals Evergreens usually have complete change of leaves every two to seven years.


Life Span of Plants : Life Span of Plants Abscission involves changes in abscission zone at the base of the petiole. Young leaves produce hormones that inhibit development of specialized layers of cells in the abscission zone. Cells become impregnated with suberin. Separation layer develops on the side of the leaf blade; cells of the separation layer divide, swell, and become gelatinous.


Leaf Abscission : Leaf Abscission