2007-2008

DomainEubacteria

DomainArchaea

DomainEukarya

Common ancestor

Kingdom: Plants

Domain Eukarya

Plant Diversity

non-vascularland plants

seedless vascular plants

Gymnospermpollen &

“naked” seeds

Angiospermflowers & fruit

pollen & seeds

vascular system = water conduction

mosses ferns

conifersflowering plants

colonization of land

flowers

Evolution of Land Plants

• 500 mya land plants evolved

– special adaptations for life on dry land• protection from drying (cuticle)

• gas exchange (through stomata)

• water & nutrient conducting systems

• seeds

Basic Plant Anatomy

Growth in Plants • Specific regions of growth: meristems

– stem cells: perpetually embryonic tissue– regenerate new cells

rootshoot

Angiosperm: Flowering Plants

Alternation of Generations

Seed & Plant embryo• Seed offers…

– protection for embryo

– stored nutrients for growth of embryo

seed coat

endosperm(3n)

cotyledons

embryo (2n)

cotyledons = “seed” leaves,first leaves of new plantcotyledons = “seed” leaves,first leaves of new plant

Slide #17

Hormone-producing

cells

Target cells

Movement of hormone

Hormone Action on Plants

A. Plant cells can produce hormones: which are

chemical messengers that travel throughout the plant causing other cells called target cells to respond.

B. In plants, hormones control:

1. Plant growth & development

2. Plant responses to environment

Cells in one blooming flower signals other

blooms using hormones to open.

Transition to reproduction

Vegetative phase

Reproductive phase

When to flower is a matter of the survival

of species

Plant hormones

• auxin• gibberellins• abscisic acid• ethylene• and more…

Control Systems in

Plants

Auxin • Effects

– controls cell division & differentiation

– phototropism• growth towards light• asymmetrical distribution of auxin (lateral movement)• cells on darker side elongate faster

than cells on brighter side

–

Mechanism of Auxin

GibberellinsCause Growth

• Family of hormones– over 100 different gibberellins identified– What they do depends on type and plant

• Effects– stem elongation– fruit growth– seed germination– Break dormancy and germinate

Abscisic acid (ABA)• Effects

– slows growth– seed dormancy

• high concentrations of abscisic acid – germination only after ABA is inactivated or leeched out

•

Ethylene• Hormone gas released by plant cells• Effects

– fruit ripening – leaf drop

• like in Autumn • apoptosis

Fruit ripening• Adaptation

– hard, tart fruit protects developing seed from herbivores

– ripe, sweet, soft fruit attracts animals to disperse seed

• Mechanism– triggers ripening process

• breakdown of cell wall– softening

• conversion of starch to sugar– sweetening

– positive feedback system• ethylene triggers ripening• ripening stimulates more ethylene production

Apoptosis in plants• Many events in plants involve

apoptosis– response to hormones

• ethylene• auxin

– death of annual plant after flowering

• senescence

– differentiation of xylem vessels• loss of cytoplasm

– shedding of autumn leaves