1 Overview of Transport in a Vascular Plant 2 TERMS TO BE REVIEWED 1 passive transport 10 chemiosmosis 2 transport proteins 11 proton pump 3 active transport 12 membrane potential ID: 932436
Download Presentation The PPT/PDF document "CHAPTER 36 TRANSPORT IN PLANTS" is the property of its rightful owner. Permission is granted to download and print the materials on this web site for personal, non-commercial use only, and to display it on your personal computer provided you do not modify the materials and that you retain all copyright notices contained in the materials. By downloading content from our website, you accept the terms of this agreement.
Slide1
CHAPTER 36
TRANSPORT IN PLANTS
1
Slide2Overview of Transport in a Vascular Plant
2
Slide3TERMS TO BE REVIEWED
1. passive transport 10. chemiosmosis
2. transport proteins 11. proton pump
3. active transport 12. membrane potential
4.
cotransport
13.
turgor
pressure5. water potential 14. plasmolysis6. osmosis7. solute concentration8. aquaporins9. tonoplast
3
Slide4I. INTRODUCTION
1. Most water and mineral absorption occurs in the cells at the tips of the roots
(Cellular Level).
2.
Root hairs
are modified epidermal cells that are specialized for water absorption.They absorb soil solution which consists of water molecules and dissolved mineral ions that are not bound tightly to soil particles.
3. Soil solution flows through the hydrophilic walls of epidermal cells and travels along the cell walls and the intercellular spaces into the root cortex
4. Movement of soil solution into the cell involves: osmosis, diffusion, active transport, proton pumps,
aquaporins, water potential, cotransport, transport proteins4
Slide5II. THREE
MAJOR PATHWAYS OF TRANSPORT IN PLANTS
A.
Transport is also regulated by the
compartmental structure of plant cells
B. The
plasma membrane
directly controls the traffic of molecules into and out of the protoplast
The plasma membrane is a barrier between two major compartments, the cell wall and the cytosolC. The third major compartment in most mature plant cells is the vacuole, a large organelle that occupies as much as 90% or more of the protoplast’s volume The vacuolar membrane regulates transport between the cytosol and the vacuole5
Slide6Cell Compartments:
6
Cell wall
Cytosol
Vacuole
Slide7D.
In most plant tissues, the cell wall and cytosol are continuous from cell to cellThe cytoplasmic continuum is called the
symplast
The cytoplasm of neighboring cells is connected by channels called
plasmodesmata
The
apoplast
is the continuum of cell walls and extracellular spaces7
Slide8E. Water and minerals can travel through a plant root by three routes: (Short-Distance Transport)
Transmembrane
route
: out of one cell, across a cell wall, and into another cell
Symplastic
route
: via the continuum of cytosol
Apoplastic
route: via the cell walls and extracellular spacesF. Long-Distance Transport at the Whole Plant LevelInvolves movement along the vertical axis (up and down)Involves bulk flow which is the movement of fluid in xylem and phloem driven by pressure differences at opposite ends of xylem vessels and sieve tubes8
Slide9Transport Routes Between Cells
9
Slide10III. ABSORPTION OF WATER AND MINERALS BY ROOTS
10
1. Pathway:
Epidermis
cortex endodermis stele (xylem)
2.
Mineral ions enter epidermal cells by
diffusion
and active transport using carrier proteins3. Movement usually a combination of apoplastic and symplastic routes4. Only minerals and water using the symplastic route move directly into xylem5. Minerals and water using apoplastic route are blocked at the endodermis by the Casparian strip and must enter an endodermal cell to move into xylem
Slide11Lateral Transport
11
Slide1212
6.
Mycorrhiza
hyphae
absorb water and selected minerals and can enable older regions of the roots to supply water and minerals to the plants.
Mycorrhiza
Slide13IV. TRANSPORT OF XYLEM SAP
13
A. Ascent of xylem sap depends on:
1. transpiration
-the loss of water vapor from leaves and other aerial parts of the plant
2. physical properties of water
-cohesion and adhesion
B. Xylem sap
(composed of water and minerals) flows upward against gravityC. Xylem vessels are close to each leaf cellD. Water must move upward to replace that lost by transpiration E. Pushing Xylem Sap: Root PressureUsually occurs at night when transpiration is lowRoot pressure (upward push of xylem sap) is generated by accumulation of minerals in stele which lowers the water potential and forces fluid up the xylem
Slide1414
3. More water entering leaves than is transpired can result in
guttation
(discharge of water droplets at the leaf margin)
Slide15F. Pulling Xylem Sap: The Transpiration-Cohesion-Tension Mechanism
15
1. Water vapor in the airspaces of a leaf diffuses down its water potential gradient and exits the leaf via stomata by transpiration.
2. Transpiration produces negative pressure in the leaf, which exerts a pulling force on water in the xylem, pulling water into the leaf
3. Involves:
Cohesion
Adhesion
Tension (Negative Pressure)
Slide16TRANSPIRATION
16
Slide1717
4.
Cavitation
—formation of water vapor pockets in xylem that breaks the chain of water molecules and the pull is stopped
Once the water chain is broken the xylem vessels is no longer functional
Can occur during drought stress or freezing
5. Ascent of xylem sap is ultimately solar powered.
.
Slide18Ascent of Xylem Sap
18
Slide19V. CONTROL OF TRANSPIRATION
19
A. Introduction
1. About 95% of water taken in is lost by transpiration through the stomata
2. Amount of water lost by a leaf depends on the number of stomata and the average size of the opening
3.
Guard cells
, by controlling the size of stomata, help conserve water
4. Benefits of transpiration: a. Assists in mineral transfer from roots to shoots b. Reduces leaf temperatures5. If transpiration exceeds delivery of water by xylem, plant wilts.6. Rate of transpiration is greatest on a sunny, warm, dry, and windy day
Slide2020
7. Stomata are more concentrated on bottom of leaf away from the sun to reduce evaporation
8. Waxy cuticle also prevents water loss
B. How Stomata Open and Close
1. Guard Cells control stomatal diameter by changing shape.
Turgid Flaccid
Turgid Guard Cells Flaccid Guard Cells
21
Slide2222
2. When guard cells take in water, they become
turgid
and the gap between cells increases.
3. When guard cells lose water, they become
flaccid
and the gap between cells decreases.
4. Changes in
turgor pressure results primarily from the reversible uptake and loss of K+ by guard cellsStomata open—guard cells accumulate K+ and gain waterStomata closed—guard cells lose K+ and lose water5. Generally, stomata are opened during the day and closed at night.
Slide23Cells Turgid/Stoma Open Cells Flaccid/Stoma Closed
23
Slide24Cells Turgid/Stoma Open Cells Flaccid/Stoma Closed
24
Slide2525
Slide2626
6. Stoma open at dawn because:
Light stimulates guard cells to accumulate K
+
and become turgid
Decrease of CO
2
because of PS
Internal clock of guard cells (circadian rhythms—cycles that have intervals of approximately 24 hours)7. Stoma close during daytime because of:Water deficiency (environmental stress)Production of abscisic acid
Slide2727
C. Adaptations to Reduce Transpiration
1.
Xerophytes
—plants adapted to arid climates
2. Modifications of xerophytes:
small, thick leaves
thick cuticle
store water in fleshy stems during rainy seasonstomata concentrated on lower leaf surfacestomata may be located in depressionsCAM pathway for PS
Slide28VI. TRANSPORT IN PHLOEM
28
A. Introduction
1. Translocation
—transport of organic products of PS by phloem throughout the plant
-in angiosperms it involves sieve-tube members
-direction varies
2. Phloem
sap—aqueous solution that is mostly sucrose 3. Sugar source—an organ that is a net producer of sugar such as mature leaves 4. Sugar sink—an organ that is a net consumer or storer of sugar, such as a tuber or bulb
Slide2929
B. Movement of phloem sap
Phloem sap moves from source to sink
Direction of flow depends on location of sugar source and sugar sink which depends on the season
Sugar is first loaded into sieve-tube members before moving to the sink.
4. Can involve:
Symplastic
and/or
apoplastic routesTransfer cells—modified companion cells with structures which increase cells’ surface area and enhance transfer between apoplast and symplastActive transport and cotransport
Slide30Loading of Sucrose into Phloem
30
Slide3131
5. Sugar will diffuse from phloem to the sink.
6. Water follows by osmosis.
C. Pressure Flow (Bulk Flow) of Phloem Sap in Angiosperms
1. Phloem sap moves by
bulk flow
driven by positive pressure (pressure flow)
2. Higher levels of sugar at the source lowers the water potential and causes water to flow into the tube 3. Xylem recycles the water from sink to source.
Slide32Pressure Flow in a Sieve Tube
32