1

Plant Reproduction

Chapter 41

2

Flower Initiation

3

Flowering Response to Daylength

4

Plants Can “Remember”

5

Flowering Model

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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

7

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

androeciumstamens made up of filament and

anther

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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 ovarystyle - slender neckstigma – pollen receptive structure

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Angiosperm Flower

10

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

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Pollen Grain and Embryo Sac Formation

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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.

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Pollen Tube Formation and Fertilization

14

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.

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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.

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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.

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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.

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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.

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Self-Pollination

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

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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.

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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.

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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.

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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.