Transcript Ch 036 Transpiration

Chapter 36~ Transport in Plants
Review of Transport
Transport proteins
Selective channels
Proton pump
Cotransport
chemiosmosis
Transport in Plant cells
 Different b/c of cell wall
 Water potential: combine effect of solute conc. And
pressure
 Water moves from area of higher potential to area of lower
potential
 Solutes lower water potential
 Megapascals (MPa) (1MPa = 10 atmosphere of pressure
 Combined pressure effect and solute concentration

Ψ= Ψp + Ψs
 Flaccid cell, plasmolyze, turgor pressure
Transport Overview
 1- uptake and loss of water
and solutes by individual
cells (root cells)
 2- short-distance transport
from cell to cell (sugar
loading from leaves to
phloem)
 3- long-distance transport
of sap within xylem and
phloem in whole plant
Water Cohesion
Whole Plant Transport
 1- Roots absorb water and dissolved minerals
from soil
 2- Water and minerals are transported upward
from roots to shoots as xylem sap
 3- Transpiration, the loss of water from leaves,
creates a force that pulls xylem sap upwards
 4- Leaves exchange CO2 and O2 through
stomata
 5- Sugar is produced by photosynthesis in leaves
 6- Sugar is transported as phloem sap to roots
and other parts of plant
 7- Roots exchange gases with air spaces of soil
(supports cellular respiration in roots)
Xylem
Phloem
Transport within tissues/organs
Three Short Routes
 Tonoplast
vacuole membrane
 Plasmodesmata (components)
cytosolic connection
 Symplast route (lateral)
cytoplasmic continuum
 Apoplast route (lateral)
continuum of cell walls
 Transmembrane Route (lateral)
 Bulk flow (long distance)
movement of a fluid by
pressure (xylem)
 All substances must pass through
cell membrane at some
time…..WHY?
Absorption by Root Hairs
Soil to Xylem
Mycorrhizae: fungus w/root hairs
Selectively permeable cell
membrane (endodermis)
Casparian Strip: suberin, waxey
substance of endodermis
Substance must cross plasma
membrane of endodermal cell to
enter the stele via the symplast.
Transport of Xylem Sap
 Transpiration: loss of water
vapor from leaves pulls water
from roots (transpirational
pull); cohesion and adhesion
of water
 Root pressure: at night (low
transpiration), roots cells
continue to pump minerals
into xylem; this generates
pressure, pushing sap
upwards; guttation
Generation of Transpiration Pull
 Root Pressure/Guttation: root push of water up xylem.
More water enters leaves than is transpired.
 Xylem Sap: Trans. Pull:
 Mesophyll cells w/ air spaces
 Spaces w/ water vapors….Air outside is drier
 Outside has lower water potential than inside.
 Water leaves leaf
Transpiration Control
 Photosynthesis-Transpiration Compromise
Needs Carbon Dioxide to produce Sugar, Open Stomata’s
90% of water lost from stomata’s
600g water lose per 1g CO2 incorporated into carbohydrate
C4 plants 300:1 ratio
Close stomata’s cause to much water loss, no CO2 for photosynthesis
•Transpiration results is evaporative cooling
Stomata’s
Guard Cell’s: shape changing, thick non-uniform
cell wall, osmosis.
Loss/Gain of K+,
Open Stomata’s GS uptake of K+ 
Ψ
become more negative Water moves in by osmosis.
K+ passive; coupled with generation of membrane
potential by proton pump
Aquaporins
 Specific Channels for passive transport of water, protein. Do
not affect water potential.
 May form gated channels
 Stomata’s open during day/closed at night.
 Stomata Cues
 Light: Blue Light Receptors
 Depletion of CO2
 Internal Clock (circadian rhythm)
Translocation of Phloem Sap
 Sugar Source: plant organ where sugar is being produced
 Sugar Sink: organ that is net consumer/storer of sugar:
growing roots,
shoot tips,
stems,
Fruit
 Tuber or Bulb may be source or sink depending on season.
Phloem Loading/Unloading
Sugar Loaded into Seive Tubes
Symplastic Route
Apoplastic Route
Combination of both:
Companion Cell accumulate sugar and pass to seive tube cell.
Accumulate 3-4x Concentration higher
Active Transport
Numerous ingrowths, adaptation, increase surface area
Transfer Cells
Pressure Flow
Phloem Sap moves at rate of 1m/hr. To fast for
diffusion or cytoplasmic streaming.
Bulk Flow driven by pressure
High Solute [ ] at source end,
lower water potential
Water flow into tube at source
Pressure greater at source end
Water loss at sink end
Decrease pressure at sink end.
Water flow from source to sink carrying sugar along
Water Recycled from phloem to xylem
Translocation of Phloem Sap
 Translocation: food/phloem transport
 Sugar source: sugar production organ
(mature leaves)
 Sugar sink: sugar storage organ (growing
roots, tips, stems, fruit)
 1- loading of sugar into sieve tube at source
reduces water potential inside; this causes
tube to take up water from surroundings by
osmosis
 2- this absorption of water generates
pressure that forces sap to flow alon tube
 3- pressure gradient in tube is reinforced by
unloading of sugar and consequent loss of
water from tube at the sink
 4- xylem then recycles water from sink to
source