Life: the Science of Biology

Lecture Notebook to accompany

Sinauer Associates, Inc. MacMillan

Copyright © 2014 Sinauer Associates, Inc. Cover photograph © Alex Mustard/naturepl.com. This document may not be modified or distributed (either electronically or on paper) without the permission of the publisher, with the following exception: Individual users may enter their own notes into this document and may print it for their own personal use. 0035 Transport in Plants

O2 (product of photosynthesis)

CO2 (reactant of photosynthesis)

H2O (transpiration)

H2O, carbohydrates, CO2 enters and O2 etc. and H2O exit the leaves via the stomata (see Figure 35.8).

H2O and dissolved minerals

35.1 The Pathways of Water and Solutes in a Plant (Page 727)

LIFE The Science of Biology 10E Sadava Sinauer Associates Morales Studio Figure 35.01 Date 07-13-12

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(A)

In this tube, the solute In this tube, a piston is potentials on the two used to increase the sides of the membrane The right side of the The water potentials pressure potential of of the two sides are differ, but the pressure tube has a lower water the right side. potentials are the potential, so there is a equal, so there is no same. net movement of net movement of water to the right. water.

Solution Solution yp = +1.0 MPa yp = 0 MPa Pure water = –1.0 MPa y = –1.0 MPa Pure water ys Membrane s y = 0 MPa y = 0 MPa = 0 MPa y = –1.0 MPa y

(B) The cell has a The inside of the cell negative solute The pressure potential of the cell balances its has a lower solute The cell has a lower potential, but has potential than the a positive pressure solute potential, so the water potential than cell’s water potential is surrounding water. the water outside, so potential. The cell has a zero. There is no net there is net movement movement of water. pressure potential of water into the cell. of zero. Flaccid cell Turgid cell = +1.0 MPa yp = 0 MPa yp Pure water = –1.0 MPa ys = –1.0 MPa Pure water ys y = 0 MPa y = 0 MPa y = –1.0 MPa y = 0 MPa 35.2 Water Potential, Solute Potential, and Pressure Potential (Page 728)

The cells of this plant have low turgor pressure and the plant is wilted.

LIFE The Science of Biology 10E Sadava Sinauer Associates The water potential of cells Morales Studio of this plant is zero because Figure 35.02 Date 07-13-12 the negative solute potential is balanced by an equally positive pressure potential. The plant is upright because its cells are turgid.

35.3 A Wilted Plant (Page 728)

LIFE The Science of Biology 10E Sadava Sinauer Associates Morales Studio Figure 35.03 Date 07-13-12 Chapter 35 | Transport in Plants 4

1 A proton pump generates 2 The difference in 3 Symport couples the dif- differences in H+ concentra- electric charge causes fusion of H+ to the transport tion and electric charge cations such as K+ to (against an electrochemical across the membrane. enter the cell. gradient) of anions such as Cl– into the cell. Outside H+ + of cell H+ H + + H H + – + H Cl H+ H H+ Plasma K+ H+ membrane Symport protein

Proton Potassium pump channel + + K ATP K H+ H+ ADP + K+ Cl– Pi Inside K+ K+ – – Cl of cell Cl

35.4 The Proton Pump in Transport of K+ and Cl– (Page 729)

LIFE The Science of Biology 10E Sadava Sinauer Associates Morales Studio Figure 35.04 Date 07-13-12

Cell membrane Plasmodesmata Cytoplasm Cell wall Water and solutes can move in the symplast by crossing a cell membrane and passing through plasmodesmata.

Water and solutes can move through the apoplast without passing through cell membrane.

35.5 Apoplast and Symplast (Page 729)

LIFE The Science of Biology 10E Sadava Sinauer Associates Morales Studio Figure 35.05 Date 09-11-12 Chapter 35 | Transport in Plants 5

The Casparian strip prevents water and solutes in the apoplast from passing between the endodermal cells into the stele.

Epidermis Root hair Endodermis Cortex Cortex Endodermis Pericycle Pericycle Xylem Stele Casparian strip

Soil solution

Apoplast

Symplast Inside the stele, solutes are actively At the Casparian strip, transported into water and solutes in Plasmodesmata the apoplast and the apoplast must water follows enter the symplast to Water and solutes travel through passively, forming cross the endodermis. the symplast or apoplast until the xylem sap. they reach the endodermis.

35.6 Pathways to the Root Xylem (Page 730)

LIFE The Science of Biology 10E Sadava Sinauer Associates Morales Studio Figure 35.06 Date 09-10-12

3 Tension pulls water from the veins into the apoplast of the Leaf mesophyll cells...

Vein 4 ...then pulls the water column through the veins in the leaves...

2 Water evaporates from mesophyll cell walls. Mesophyll Stem cell H2O 5 ...and then upward in the xylem of the root 1 During transpiration and stem. water vapor diffuses out of the stomata. Xylem

O H H H H O H H O H H O Root 6 Water molecules form a cohesive H2O water column from the roots to the leaves.

7 Water moves H2O into the xylem by osmosis.

Xylem 8 Water enters the root from the soil by osmosis.

35.7 The Transpiration–Cohesion–Tension Mechanism (Page 731)

LIFE The Science of Biology 10E Sadava Sinauer Associates Morales Studio Figure 35.06 Date 07-13-12

Without pressure With pressure

2 …so that xylem sap is 1 By applying just pushed back to the cut enough pressure… surface of a plant sample,…

3 …a scientist can determine the tension on the sap in the living plant.

Pressure gauge Gas pressure

Pressure release valve

(Page 732)

Life10e_35.07 Sinauer 7-11-12

(A)

Guard cells

Stoma 10 µm

(B) Cl– K+ 1 In the light, guard cells H+ actively pump protons out, thus facilitating the entry of K+ and Cl–.

2 Higher internal K+ and Guard Cl– concentrations give cells H O guard cells a more 2 negative water potential, causing them to take up water, increase in pressure, and stretch, opening the stoma.

Stoma Cellulose microfibrils

+ H2O K 3 In the absence of light, + – Cl– K and Cl diffuse passively out of the guard cells, and water follows by osmosis. The guard cells shrink and the stoma closes.

35.9 Stomata (Page 733) Remove a ring of Organic solutes accumulate bark to girdle the tree. in the phloem above the girdle, causing swelling.

Time Bark LIFE The Science of Biology 10E Sadava Sinauer Associates Morales Studio Wood Figure 35.08 Date 07-13-12 In-Text Art (Page 734)

LIFE The Science of Biology 10E Sadava Sinauer Associates Morales Studio Figure 35.UN1 Date 07-13-12 Chapter 35 | Transport in Plants 9

Pores of sieve plate

Sieve plate

Mature sieve tube elements do not have nuclei and have lost most of their organelles.

Sieve tube element

Phloem sap

The companion cell is a fully functional cell with a nucleus.

Companion cell Sieve plate

Dr. R. Kessel & Dr. G. Shih/Visuals Unlimited. Pores 35.10 Sieve Tubes (Page 735)

Sieve tube element

LIFE The Science of Biology 10E Sadava Sinauer Associates The aphid’s stylet Morales Studio has successfully Figure 35.09 Date 07-13-12 penetrated the sieve tube.

Sap droplet Longistigma caryae (aphid) Stylet In-Text Art (Page 735)

LIFE The Science of Biology 10E Sadava Sinauer Associates Morales Studio Figure 35.UN2 Date 07-13-12 Chapter 35 | Transport in Plants 10

2 Source cells load sucrose Phloem Source into phloem sieve tubes, sieve cell reducing their water Xylem tube potential…

1 Transpiration H O pulls water up 2 H O xylem vessels. 2 Sucrose 3 …so water is taken up from xylem vessels by osmosis, raising the pressure potential in the sieve tubes. H2O 4 Internal pressure Sink cell differences drive the sap along the sieve tube to sink cells.

H2O Sucrose

5 Sucrose is unloaded into sink cells, increasing 6 …and water moves the water potential in the back to xylem vessels. sieve tube…

35.11 The Pressure Flow Model (Page 736)

LIFE The Science of Biology 10E Sadava Sinauer Associates Morales Studio Figure 35.10 Date 07-13-12 TablE35.1 Mechanisms of Sap Flow in Plant Vascular Tissues Xylem Phloem Driving force for Transpiration from Active transport of bulk flow leaves sucrose at source and sink Site of bulk flow Nonliving vessel Living sieve tube elements and tracheids elements Pressure Negative (pull from top; Positive (push from potential in sap tension) source; pressure)

(Page 736)

HYPOTHESIS Reducing the sucrose concentration in a sink organ will increase the transport and unloading of sucrose from the phloem.

Method Plants were transformed with a gene for invertase, an enzyme that hydrolyzes sucrose.

The potato plant has underground tubers, modified stems that store starch.

Results Wild-type plants Transgenic plants Phloem Tuber sink cell Sucrose

The wild-type plants had a high The genetically modified plants level of sucrose in developing had a low level of sucrose in tubers. The tubers were normal developing tubers and produced in size and number. fewer but much larger potatoes.

CONCLUSION Increasing sink strength increases sucrose transport into developing tissues. Go to BioPortal for discussion and relevant links for all INVESTIGATINGLIFE figures.

(Page 737)

Life10e_35.11 7-12-11