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Chapter 36: Transport in Plants
Figure 36.1 An overview of transport in whole plants (Layer 4)
1.
Role of phloem in transporting
phloem sap
2.
Respiration in roots
3.
Root absorption of water and
minerals
4.
Xylem flow of water
5.
Transpiration
Figure 36.2 A chemiosmotic model of solute transport in plant cells
Figure 36.3 Water potential and water movement: a mechanical model
Figure 36.4 Water relations of plant cells
Figure 36.5 A watered tomato plant regains its turgor
Figure 36.6 Compartments of plant cells and tissues and routes for lateral transport
Figure 36.7 Lateral transport of minerals and water in roots
Figure 36.9 Guttation: caused by root pressure
Figure 36.10 The generation of transpirational pull in a leaf
Figure 36.11 Ascent of water in a tree
Figure 36.12 An open (left) and closed (right) stoma of a spider plant (Chlorophytum
colosum) leaf
Figure 36.12x Stomata on the underside of a leaf
Figure 36.13a The mechanism of stomatal opening and closing
Figure 36.13b The mechanism of stomatal opening and closing
The Physiology of Stomatal Opening
•
Three Cues
•
Light causes the guard cells to accumulate potassium ions
and thus increase turgidity.
•Blue-light receptor in the guard cells which senses light
and activates a pump (ATP required) to uptake potassium
ions.
•
CO2 Depletion within the leaf air spaces. This occurs right
at the beginning of PS.
•
Internal Clock: which operates even if you keep the plant
in the dark so the plant has some sort of internal
mechanism for regulating the opening of the stomates.
The Physiology of Stomatal Closing
•
Water Deficiency
•
Hormonal control (abscisic acid) produced in responses to
drought conditions will cause guard cells to close the stomata.
•
High Temperatures: may occur by increasing carbon dioxide
levels within the leaf as respiration increases
Figure 36.15 Structural adaptations of a xerophyte leaf
1.
Thickened cuticle
2.
Outermost (dermal) tissue is
multilayered
3.
Stomata are recessed in pits.
4.
Hairs or trichomes create a
protected layer of water vapor near
the leaf.
Phloem translocates its sap from sugar sources to sugar sinks
•
Sucrose made during PS will travel symplastically.
•
It can leave the symplast and then travel apoplastically
•
From the cell wall it can then be “dumped into” or loaded into
the companion cells and sieve tube members thus increasing
the concentration of sugar in these cells.
•
This movement into the companion cells and sieve tube
members is thought to be done with the help of proton
pumps.
•
The hydrogen ions that are pumped into the apoplast are
then cotransported with the sucrose back into the
companion or sieve tube cell.
Figure 36.16 Loading of sucrose into phloem
Figure 36.17 Pressure flow in a sieve tube
1.
As sucrose gets loaded into the
sieve tube members the water
potential goes down.
2.
Water then enters the sieve tube
member from a neighboring
xylem vessel.
3.
This causes the buildup of
pressure, hydrostatic pressure
which forces the sap to flow.
4.
Since sucrose is being taken up
at a “sink”, water pushes the
sucrose in that direction.
Figure 36.18 Tapping phloem sap with the help of an aphid
Figure 36.0 Eucalyptus trees
Figure 36.0x Trees
Figure 36.1 An overview of transport in whole plants (Layer 1)
Figure 36.1 An overview of transport in whole plants (Layer 2)
Figure 36.1 An overview of transport in whole plants (Layer 3)
Figure 36.8 Mycorrhizae, symbiotic associations of fungi and roots
Figure 36.14 A patch-clamp study of guard cell membranes
Figure 36.15x Structural adaptations of a xerophyte leaf