Plant Reproduction Chapter 41

Flower Initiation

Flowering Response to Daylength

Plants Can “Remember”

Flowering Model

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 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 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

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

Pollen Grain and Embryo Sac Formation

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.

Pollen Tube Formation and Fertilization

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

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 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 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 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.