2-7-11 Transport in Vascular Plants II

2-7-11 Transport in Vascular Plants II -...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: II.


Water
and
mineral
acquisi2on
at
roots Transport
in
Vascular Plants
II I. Usually
only
a
few
cells
and very
short
distance
from soil
to
vascular
cylinder

for roots
taking
up
resources Proper(es
of
water,
osmosis and
turgor
pressure II. Water
and
mineral
acquisi2on III. Transpira(on
and
Xylem transport IV. Phloem
transport 1 How
do
water
and
minerals
get from
the
soil
to
the
vascular
(ssue? Root
hairs with
no
cu(cle 2 Crossing
the
cell
membrane: Passive transport Active transport Most
solutes ‐facilitated
diffusion
& ac(ve
transport
via membrane
proteins (Plasmodesmata,
narrow symplas(c
channels
between plant
cells,
selec(ve) Ini(al
pathways
(soil
to
endodermis) 1.Apoplas2c
( “non‐living”
space) 2.Symplas2c
(“living
space”) 3.transmembrane 3 • But,
on
the
route
to
vascular
(ssue water
and
nutrients
MUST
 cross cell
membrane
at
the
endodermis, because
of
Casperian
strip
(waxy, suberin) Water ‐some

molecules through
membrane, some
through aquaporins ‐process
is
osmosis ‐driving
force
is
Ψ Diffusion gradient ATP Facilitated diffusion Fig. 7-17 ‐What
is
nutrient
uptake
doing
to
the
Ψ
in
the
root
cells? ‐Why
does
water

move
into
root
cells? 4 Q1?
Forcing
water
and
solutes
across
cell membrane
at
endodermis
does
all
EXCEPT a. Controls
entry
of
solutes
into
vascular
2ssue b. Controls
entry
of
water
into
vascular
2ssue c. Makes
the
whole
plant
approximate
one
big osmometer d. Results
in
higher
solute
concentra2ons
in
the xylem 5 6 Next,
crossing
from
symplast
to xylem: Symplast











Apoplast
 Endodermis

‐>

Xylem Q2?
For
water
to
move
from
parenchyma roots
cells
into
mature
xylem
cells,
the
xylem must
have a. Higher
Ψp b. Lower
Ψs ‐Where
is
osmosis
occurring
in
this
diagram? ‐Why
is
mature
xylem
considered
apoplast? Properties of water, osmosis and turgor pressure II. d. Lower
Ψ e. Higher
Ψ Once
water
and few
nutrients

in xylem,
now
ready for
long
distance transport I. c. Higher
Ψs Xylem 7 8 III.

Transpira2on
and
Bulk
Flow Transpira(on
=
loss
of
water from
the
shoot
system
to
the surrounding
environment. Water and mineral acquisition sugar ‐What
is
actually
driving
water
loss? III. Transpiration and Xylem transport IV. Phloem transport -1.0 MPa 9 How
is
water
lost
in
transpira(on
replaced? (correction in text Fig 36.15, Ψ of leaf air spaces should be ~ the same as cell walls, as indicated above) 10 Now:

Water
is
leaving
xylem
in
leaf,

crea(ng
tension
(i.e. nega(ve
pressure
or
Ψ p)
in
the
“pipe” 
of
dead
xylem • Water
is
PULLED
up
the
plant
in
the
xylem,
by process
of
bulk
flow
or
pressure
flow,
i.e. moves
from
less
nega(ve
to
more
nega(ve

Ψ p ‐Cohesion‐tension
theory • Why
is
water
movement
in
xylem
bulk
flow
(in response
to
Ψ p gradient)
instead
of o smosis (in
response
to
a
Ψ gradient)? 1)
Surface
tension
generated
by “capillarity”
of
water
in
mesophyll
cell walls
(apoplast):
nega2ve
Ψp and thus Ψ (Ψ =Ψs + Ψp) • Ring/spiral
wall
thickening
of
lignin
protects against
vessel
collapse
(sclerenchyma) 2)Water
moves
from
living
cells
to
cell walls
by
osmosis
due
to
gradient
in
Ψ 3)Water
moves
from
xylem
to
living cells
by
osmosis
due
to
gradient
in
Ψ 11 12 How
is
transpira(onal
water
loss
regulated? Xylem sap Tiny
amounts
of dissolved
nutrients and
hormones,
are carried
along
by the
bulk
flow
in the
“xylem
sap” Mesophyll cells Stoma Leaf ψ ( air spaces) = −-1.0 MPa 7.0 Mpa Transpiration Leaf ψ ( cell walls) = − 1.0 Mpa Trunk xylem ψ = − 0.8 Mpa • Leaves
generally
have
broad
surface areas
and
high
surface‐to‐volume ra(os Water molecule Atmosphere • Increases
poten(al
for
photosynthesis • Also
increases
poten(al
for
water
loss Adhesion by hydrogen bonding Cell wall Xylem cells Water potential gradient Evapora(ve
water loss
from
leaves (transpira(on)
sets up
Ψ gradient 
that “pulls”
water
up through
plant,
like
a hydraulic
rope Outside air ψ = − 100.0 Mpa Cohesion and adhesion in the xylem • But,
most
leaf
epidermal
cells
covered with
cu(cle
that
prevents
water
loss over
most
of
surface • Stomata,
special
epidermal
cells,
help regulate
the
rate
of
transpira(on Cohesion by hydrogen bonding Water molecule Root hair Trunk xylem ψ = − 0.6 Mpa Soil particle Soil ψ = − 0.3 Mpa Water Water uptake from soil Fig. 36-15 H+ pumped out 13 How
much
water
is
used? Stomatal movements: K+ flow in 14 Why? H 2 O flow in >
90%
of
water
taken
up
is transpired
(lost
to
air) Why? s tomata open Why? -1.0 MPa … but
necessary
for
CO2 uptake Reverse
process
to
close. … where
does
rest
go? K
‐channels,
aquaporins
and radially
oriented
cellulose
fibers play
important
roles. Transpira(on: • Cools
leaf • transport
minerals
from roots
to
shoot Peak
velocity
of
xylem
sap: 15‐45
m/hr What
is
wrong
with
how
water
is
pictured
in
the
soil? 15 Adapta(ons
for
water
conserva(on How
much
water
does
it
take
to
make
one
serving
of…. Food: High
root/shoot
biomass ra(o
and
deep
roots,
e.g. this
juniper
in
Texas Gallons
of
water: Leeuce Almonds Steak 16 Rehydra(ng
drier
soil
layers at
night
(hydraulic
lil)
when transpira(on
minimal,
e.g. this
sagebrush
in
Utah ~
3 ~80 >2000 hep://www.ckf.com/info/almonds.cfm Source:
Water
Educa(on
Founda(on,
Water Inputs
in
California
Food
Produc(on,
1991 17 At
places
in
the Atacama
desert
where no
precipita(on
has even
been
recorded, some
plans
trap
fog
off the
Pacific
Ocean
as only
water
source Redwood
tress,
apparently near
the
limit
of

“ pulling” water
from
soil,
also
trap
fog as
a
leaf
water
source 18 Adapta(ons
for
water
conserva(on Oleander:
leaves
with
thick cu(cle
and
stomatal
“crypts”
that reduce
evapora(ve
water
loss sugar I. Properties of water, Osmosis and turgor pressure II. Water and mineral acquisition III. Transpiration and Xylem transport Oco(llo,
leaves
are drought
deciduous, carries
out
minimal amount
of
“stem” photosynthesis
when leafless ”old
man”
cac(:
leaf hairs
to
reflect
sun (keeping
them
cooler), and
CAM photosynthesis
so stomata
open
mostly
at night IV. Phloem transport 19 IV.


Phloem
transport,
Angiosperms
 20 Phloem
sap
composi(on: • • • • • ‐Transports
mostly
sugars
(in
water)
in
highly specialized
living
parenchyma
cells:
sieve cells
stacked
in
pipes
and
connected
via sieve
plates ‐Accompanied
by
companion
cells ‐Direc(on
of
flow
is
sugar
source
to
sugar
sink Mostly
sugars
(mainly
sucrose) amino
acids hormones minerals enzymes Aphid
 30%
dry
maeer
(of
which
80%
is
sugar) How
do
we
know
what
is
in phloem
sap? What
would
happen
if
aphid inserted
stylet
in
xylem
instead? Sieve
element Aphid
stylet 21 How
do
sugars
get
in
and
out
of

phloem? 
Mesophyll
Cell
 Chloroplast stroma cytoplasm
 22 Q3?
When
would
you
expect
phloem transport
from
roots
to
shoots
an
red
oak tree
in
Athens? Phloem Apoplast
or
symplast pathway
for
loading Why
does
water
flow
into
the
sieve tubes
at
source? a. Winter,
when
no
leaves b. Spring,
when
new
leaves produced c. Summer,
when
full
canopy d. Fall,
as
leaves
dropping Then
at
sink,
why
does
water
flow
out? But,
what
about
WITHIN
phloem? Process
for
transport? 








 ‐Bulk
flow,
higher
to
lower
pressure
poten2al
(Ψp) Driving
force? ‐Posi2ve
pressure
gradient How
can
bulk
flow
(pressure
flow)
be
the
mechanism
if
phloem cells
are
alive? 23 24 Study
exercise:
Compare
xylem
and
phloem How
are
they
similar? How
are
they
different? 25 ...
View Full Document

Ask a homework question - tutors are online