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Plant Reproduction
Chapter 41
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Flower Initiation
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Flowering Response to Daylength
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Plants Can “Remember”
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Flowering Model
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Evolution of the Flower
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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
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Floral Evolution
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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
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Floral Evolution
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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
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Angiosperm Flower
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Formation of Angiosperm Gametes
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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
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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
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Pollination
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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.
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