Reproduction with Cones and Flowers

Chapter 22

Alternation of Generations

All plants have a diploid sporophyte generation and a haploid gametophyte generation

Gametophyte plants produce sperm and eggs

Fertilization begins the sporophyte generation

Generations cont.

Actual plant is the diploid sporophyte generation

Gametophytes are found in cones or flowers

Pollen cones and seed cones

Pollen cones (male) produce male gametophytes or pollen grains– One haploid nuclei will develop into 2 sperm

Seed cones (female) produce female gametophytes contained in the ovules– Each ovule contains a few eggs for fertilization

Pollination

Gymnosperm life cycle takes 2 years for completion

Male cones release pollen which is carried by wind to female cones

Fertilization and development

Pollen grains stuck to female cones will develop a pollen tube containing the 2 sperm

One sperm disintegrates, the other fertilizes the egg to make a diploid zygote

Zygote grows into an embryo which is enclosed in a seed

Flower structure

Flowers are reproductive structures Have four parts

– Sepals– Petals– Stamens– Carpels (pistils)

Sepals and petals

Sepals– Outermost circle of parts (green)– Protect the bud before it opens

Petals – Usually brightly colored– Found inside the sepals– Attract pollinators

Stamens and carpels

Stamen– Filament-long, thin stalk that supports anther– Anther-sac at end of filament that contains pollen

grains Carpel (pistils)

– Ovary-broad base containing one or more ovules– Style-narrow stalk extending from top of ovary– Stigma-sticky section on top of style that collects

pollen

Complete and incomplete flowers

Complete flowers– Contain all flower parts: sepals, petals, stamen,

carpel Incomplete flowers

– Missing one or more flower parts– Often seen in plants that produce separate male

and female plants– Or in plants that have separate male and female

flowers (on same plant)

Angiosperm life cycle

Flowers are produced Meiosis occurs in the anther to produce

pollen grains Meiosis occurs in the ovary to produce the

embryo sac which contains the egg and endosperm nuclei

Pollination

Pollen picked up by pollinator and carried to stigma

Some wind pollinated More efficient pollination by insects or

animals

Fertilization

Once pollen reaches a stigma, pollen tube develops and grows into the ovule

2 sperm nuclei develop Double fertilization occurs

– One sperm fertilizes the egg to make the zygote– One sperm fertilizes the endosperm to make a

triploid cell or endosperm (food for the embryo)

Seed development

After fertilization, nutrients flow into flower tissue to support development of embryo and seed

Ovary walls thicken to make fruit to protect the seeds

Ovule toughens to become seed coat FRUIT-is any seed enclosed within the

embryo wall; includes common fruits, vegetables, nuts

Seed dispersal

Animals – Seeds usually found in fleshy fruits; can pass

through digestive tracts unharmed– Deposited in new areas with animal feces

Wind and water– Usually light weight seeds– Can float on air currents or in water– Carried to far places or remote places (islands)

Seed dormancy

Embryo is alive but not growing Length of dormancy varies in each plant Allows for long-distance dispersal Environmental factors cause seeds to end

dormancy and germinate

Seed germination

Early growth stage of embryo Seeds must absorb water to crack seed coat Root emerges first Shoots emerge next

– Can be protected by a sheath (monocots)– Can be protected by the cotyledons or a “shoot

arch” (dicots)

Vegetative reproduction

Asexual form of reproduction Produce many plants from horizontal stems

(stolons), plantlets, or underground roots No pollination or seeds New plants are genetically identical to

parent plant

Plant propagation

Use cuttings or grafting or budding from original plant to produce offspring from seedless plants

Avoids genetic variation Preserves wanted characteristics

Cuttings

Pieces of stem with buds containing meristematic tissue

Stem is partially buried in soil Usually use rooting powders to stimulate

root growth

Grafting and budding

Grafting – Plants with poor roots grown on plants with

strong roots– Stem is cut (scion) and attached to another

plant (stock)– Words bests when plants are dormant– Vascular tissues of scion / stock must connect

Budding – Using buds for scions instead of stems

Plant hormones and responses

Hormone- chemical messenger that stimulates or suppresses activity of cells in another area– Released in response to environmental ques– Released in response to internal changes of the

plant as part of the life cycle

Gibberellins

Hormones that produce dramatic increase in size

End seed dormancy Start germination Promote rapid growth of the seedling Increase the size of fruits Elongate stems/stalks

Ethylene

Hormone that causes ripening Naturally produced by fruits

Cytokinins

Hormones that stimulate cytokinesis (final part of cell division)

Produced in growing roots and developing seeds and fruits

Involved in the “width” growth or lateral growth of stems and branches

Slows the aging process of plant organs

Auxins

Hormones involved in lengthening plant cells of the apical meristem

Stimulate growth of primary stem Prevents growth of new branches Prevent root growth

Phototropism

Tendency of a plant to grow toward light

Thigmotropism

Response to touch– Coiling around trellises or other stems when in

contact– Curling up when touched by other organisms

Gravitropism

Positive - is growing down toward gravity (roots, stimulated by low levels of auxins)

Negative – growing up away from gravity (stems stimulated by high levels of auxins)

Photoperiodism

Plant responses to changing lengths of day/night

Longer days trigger flowering Shorter days trigger change in leaf colors

and dropping of leaves in deciduous plants