Growth, morphogenesis, and differentiation produce the plant body

• Morphogenesis is the development of body form and organization

• The three developmental processes of growth, morphogenesis, and cellular differentiation act in concert to transform the fertilized egg into a plant

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Fig. 35-29

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• The vascular tissue system carries out long-distance transport of materials between roots and shoots

• The two vascular tissues are xylem and phloem• Xylem conveys water and dissolved minerals

upward from roots into the shoots• Phloem transports organic nutrients from where

they are made to where they are needed

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Xylem has NEGATIVE water potential Phloem has POSITIVE water potential

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Aquaporins: Facilitating Diffusion of Water

• Aquaporins are transport proteins in the cell membrane that allow the passage of water

• The rate of water movement is likely regulated by phosphorylation of the aquaporin proteins

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Stimuli for Stomatal Opening and Closing

• Generally, stomata open during the day and close at night to minimize water loss

• Stomatal opening at dawn is triggered by light, CO2 depletion, and an internal “clock” in guard cells

• All eukaryotic organisms have internal clocks; circadian rhythms are 24-hour cycles

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Bulk Flow by Positive Pressure: The Mechanism of Translocation in Angiosperms

• In studying angiosperms, researchers have concluded that sap moves through a sieve tube by bulk flow driven by positive pressure

Animation: Translocation of Phloem Sap in SummerAnimation: Translocation of Phloem Sap in Summer

Animation: Translocation of Phloem Sap in SpringAnimation: Translocation of Phloem Sap in Spring

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4

Fig. 36-20

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2

1

1

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Vessel(xylem)

Sieve tube(phloem)

Source cell(leaf) Loading of sugar

Uptake of water

Unloading of sugar

Water recycled

Sink cell(storageroot)

Sucrose

H2O

H2O

Bu

lk f

low

by

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ga

tiv

e p

res

su

re

H2O

Sucrose

Bu

lk f

low

by

po

sit

ive

pre

ss

ure

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Biological Clock Regulation by the Hypothalamus

• The hypothalamus also regulates circadian rhythms such as the 24 Hour sleep/wake cycle All eukaryotic organisms have internal clocks

• Biological clocks usually require external cues to remain synchronized with environmental cycles

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The Diencephalon

The hypothalamus regulates homeostasis and basic survival behaviors such as feeding, fighting, fleeing, and reproducing

Fig. 49-UN3

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Fungi and Plant Nutrition

• Mycorrhizae are mutualistic associations of fungi and roots

• The fungus benefits from a steady supply of sugar from the host plant

• The host plant benefits because the fungus increases the surface area for water uptake and mineral absorption

• Mycorrizal relationships are common and might have helped plants to first colonize land

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Agricultural and Ecological Importance of Mycorrhizae

• Farmers and foresters often inoculate seeds with fungal spores to promote formation of mycorrhizae

• Some invasive exotic plants disrupt interactions between native plants and their mycorrhizal fungi

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• In the late 1800s, Charles Darwin and his son Francis conducted experiments on phototropism, a plant’s response to light

• They observed that a grass seedling could bend toward light only if the tip of the coleoptile was present

• They postulated that a signal was transmitted from the tip to the elongating region

Video: PhototropismVideo: Phototropism

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Fig. 39-5b

RESULTS

Light

Tipremoved

Darwin and Darwin: phototropic response only when tip is illuminated

Tip covered by opaquecap

Tip covered by trans-parentcap

Site ofcurvature covered by opaque shield

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Control of Cell Division and Differentiation• Cytokinins are produced in actively growing tissues

such as roots, embryos, and fruits• Cytokinins work together with auxin to control cell

division and differentiation

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A Survey of Plant Hormones

• In general, hormones control plant growth and development by affecting the division, elongation, and differentiation of cells

• Plant hormones are produced in very low concentration, but a minute amount can greatly affect growth and development of a plant organ

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Gibberellins

• Gibberellins have a variety of effects, such as stem elongation, fruit growth, and seed germination

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Fig. 39-10

(a) Gibberellin-induced stem growth

(b) Gibberellin-induced fruit growth

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• Circadian rhythms are cycles that are about 24 hours long and are governed by an internal “clock”

• Circadian rhythms can be entrained to exactly 24 hours by the day/night cycle

• The clock may depend on synthesis of a protein regulated through feedback control and may be common to all eukaryotes

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Fig. 39-20

Noon Midnight

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• Unit 6C35 45&screen shot, 113&130, C36 82&(C49 52/53/54), 46&47, 98&99C37 57&66

• C38 (C11)&screenshot• C39 20&21, 23&26, 38&45, 80&81

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