Chemistry Research

CHAPTER 32
The tallest tree is the Redwood (Sequoia sempervirens) approx 110 m
The tallest Angiosperm is the Australian Eucalyptus regnans
Water Uptake and transport (Fig. 32.1)
= water is essential because: transport solute, cool the body, photosynthesis and Turgor pressure
Osmosis- movement of H2) through a semi-impermeable membrane
Osmotic potential ( o)-depend on dissolve solute: Hi concentration means more negative o.

Isoosmotic-two solution with same o; Hypoosmotic- solution that has a less negative o(more +)
Turgor Pressure -hydraulic pressure result from water up take, cell turgid; analog to air pressure in a tire
Water Potential ( )-Overall tendency of a solution or cell to take up water from pure water solution.

= o + P, P is positive and is measured in MegaPascal (MPa); loss in P means the plant will wilt.

MINERAL UPTAKE
= Mineral and ions transported across membranes by protein: Pumps and Ion channel & Symport
= Use both Facilitated (low K outside cell) and Active transport (depend on Respiration).

= Plant do not have a Na/K pump but a H pump (generate membrane potential/ gradient).

= Ion transport changes Electric potential of membrane (-120mV- can be measure by electrodes)
= The traffic of ions into/out of cell can be measure by Patch clamping technique.

Apoplast & Symplast
= Water moves into the Stele (more – ) from the cortex (less – ) from the soil (more less – )
= Mineral move by Mass flow or diffusion/Active transport (via Membrane Protein)
Apoplast-movement through cell wall and intercellular space; it is continuous
Symplast- movement through the cell and b/w cell via plasmodesmata; continuous but regulated
= H2O from the Apoplast stops at the Endodermis (Stele); have Casparian strips -made of suberin
= Strip separate Apoplast of the cortex from the Apoplast of the stele (periclcle)
= Membrane protein enable enables selective mineral uptake and uptake rate.

Transfer cells -in pericycle, transport minerals from cytoplasm back into the apoplast (MP/Mit, SA, rate)
TRANSPORT IN XYLEM
Model 1-pumping cells stem; ruled out by Eduard Strasburger exp-use poison pitric acid; Stop in the leaf
= Exp. demonstrate: (1) pumping cell not responsible for uptake (2) leaves important (3) root not involve
Model 2- Capillary action ruled out because capillary action cannot support 110 m tree (40 cm)
Model 3- root pressure-based on more – in xylem & less neg in root; support by guttation
Guttation- the removal of H2O through the leaves under high humidity and a abundance of H2O in the soil
= The Oozing of sap from a cut stem of Coleus when the top is remove; not enough
= Root pressure changes, it either weaker or stronger but will not exceed 2X atm pressure
Evaporation-Cohesion-Tension mechanism (Fig. 32.8)
(1)Evaporation of H2O through stomata-increase tension &make wall more – o; H2O enter nearest vein
(2) Removal of H2O from leaf cause pull of water below; pull is send through the whole column
(3) Column is maintain by the adhesion of water to the cell wall (glass)
Summary-evaporation account for xylem transport & the resulting tension cause the cohesion
Dry Air-more – o than root–less neg than sap in xylem which is less neg in leaf–less than air
= Minerals dissolve in sap is transported to rest of the plant body by the phloem
Evaporation-Cohesion-Tension mechanism -requires tension in column or solution of the xylem
= Pressure can be measure by pressure bomb; done by Per Scholander, Fig 32.9
= In vines there is no tension in xylem until the leaves are removed; some Plants loss tension at night
TRANSPIRATION THROUGH THE STOMATA
Transpiration- is the loss of water from shoot (leaf) by evaporation; also cools the cell
= Loss is minimize by the cuticle; impermeable to CO2
Stoma- composed of specialized guard cells in the epidermis which allow passage of H2O/CO2
= In monocot it is associated with specialized epidermal cells; but mechanism is the same in dicot
= Open by pumping of K into guard cells; stretching is regulated by Microfibril
= Pumping also allow for Cl & other organic ion uptake; maintain electrical balance or neutrality
= Increase CO2 level in spaces of leaf and – (release of ABA); blue light also reduce H pumping
CAM-succulent plants-Crassulaceae-such as Kalonchoe
= Have a backward stomata cycle- opens at night; leaf tissue becomes acidic (Malic/Aspartic acid
= Adapted for environment devoid of water; loss of H2O occurs in cool environment.

TRANSLOCATION
= Occur in the Phloem- transport sugars, aa, minerals from leaf to root
Model: bi-directional, up and down the stem