Outline: Transport and Nutrition in Plants, Chpts 32, 33, Bio 102 (Vogt)

I. Plant Nutrition - simple, water soluble, inorganic compounds

II. Nutrient Transport: Mechanisms of Cellular Transport

III. Roots : Minerals / H₂O Soil INTO Xylem

active transport / osmosis

IV. Water (mineral) transport to leaves : UP Xylem
Cohesion - Tension Theory / Transpiration

V. Transport AROUND Plant: Phloem
Sucrose loading >> Osmotic Pressure >> Bulk Flow

Lecture: Transport and Nutrition in Plants, Chpts 32,33

O. Big Picture (32.1, p. 693, 33.1, p. 712)

Photosynthesis (PS) > Sugar
Minerals + Sugar + Energy (ATP) > Biomolecules

I. Plant Nutrition - simple, water soluble, inorganic compounds

A. Macronutrients

1. Air: CO₂, O₂
2. Soil: H₂O, NO₃^-, NO₄⁺, K⁺, H₂PO₄^-, HPO₄⁼, Ca⁼, Mg⁺⁺, SO₄⁼

B. Micronutrients

1. Soil: Fe⁺⁺, Fe³⁺, Cl^-, Mn⁺⁺, MoO₄⁼, Cu⁺⁺, BO₃^-, B₄O₇⁼, Zn⁺⁺

C. Macromolecules require C, O, N, S, P

1. C from CO₂ /////// O from H₂O via photosynthesis
2. Nitrogen > ammonium > nitrites > nitrates (49.11,p.1156, 33.8, p.719)

	Nitrogen Fixing Bacteria
     bacteria           bacteria
    N2----->NH4+----->NO2------>NO3-==>>>assymilation
               bacteria                    in roots

a. nitrogenase: enzyme complex N₂ >> NH₃ (>>NH₄⁺ in water)
N₂+8e^-+8H++16ATP >> 2NH₃+H₂+16ADP+16P_i
amazing prokaryotic "invention" to fix N₂ for availability into amino acids for proteins, etc.

b. multiple species of bacteria in soil, step by step

c. Symbiosis / Root Nodules: (33.9, 33.10, p.720)


certain plants contain nitrogen fixing bacteria in roots
legumes, aspen trees

d. NO₃^- converted to amino acids in root cells

3. Phosphorous (49.12, p.1157)

a. inorganic phosphate in soil: PO₄⁺⁺⁺
b. plant fungal associations: Mycorrhizae (mutualism) (33.15, p. 724)

95% of all vascular plants (p.584, p.724) (Fungi: chpt 28, p.573, 28.2 p., 575)
effectively increase root surface area for phosphate/H₂O

II. Nutrient Transport: Mechanisms of Cellular Transport

A. Cellular Transport

1. cell membrane is selectively permeable

membrane proteins: carrier proteins / channel proteins

2. Passive Transport: diffusion down a concentration gradient
3. Active Transport: movement against a concentration gradient

REQUIRES ENERGY(ATP)

4. Energy Source: Proton Pump and Membrane Voltage (32.2, p.694)

a. Proteins pump H⁺ out of plant cell (ATP consumed)
b. H⁺ out leaves inside negative: Membrane potential (voltage - battery)
c. H⁺ gradient and Membrane voltage provide energy for taking up

and concentrating soil minerals: Active Transport

5. Osmosis: (32.4, p.696)

H₂O moves down gradient from high concentration (low solute)

to low concentration (high solute).

Cell swells: Plant cell wall prevents over swelling

pressure build up = turgor pressure

B. Let's deal with transport in three steps... (32.1, p. 693)


1. Mineral and H₂O uptake in roots:

active transport of minerals, osmosis [in] of H₂O

2. Mineral, H₂O transport from roots to leaves

a. cohesion of water molecules / small diameter of xylem
b. Regulated transpiration in leaves

3. Circulation of biomolecules (sugars) - Phloem

active transport of sugar, osmotic pressure > flow

III. Roots : Soil Minerals & H₂O INTO Xylem (active transport-osmosis)

A. Two routes of entry(32.6 p.698, 32.5, p. 697)

1. Root hair cell > cytoplasmic continuum :Plasmodesma / Symplast
3. Cell wall continuum - extracellular space between cell walls

B. Mineral uptake - against concentration gradient ([K⁺cell] = 10*[ K⁺soil])

1. Active uptake into root hair cytoplasm

a. Root hairs are specialized epidermal cells.
b. Root hairs create huge surface area / absorptive surface.
c. ATP driven active uptake

K⁺: ion channels, attracted by negative internal charge
NO₃^-: cotransport in with H⁺ (H⁺ gradient)
2. Diffusion into cytoplasmic continuum

a. Cytoplasm of adjacent root cells joined - plasmodesmata
b. cytoplasmic continuum = "cytoplasmic net"
c. minerals entering cytoplasm of one cell move directly into

cytoplasm of the next cell, and so forth

d. minerals eventually arrive in cytoplasm of endodermal cell

3. selective transport out of endodermal cell into extracellular space

of vascular column: Endodermal cells / Casparian Strip
prevents passive movement between xylem and root cortex.

4. Diffusion into xylem tubes.
5. Summary, mineral movement:

a. active transport: into root hairs.
b. passive transport (diffusion) through symplast to endodermis.
c. active transport across endodermal cell layer.
d. passive transport (diffusion) into xylem.

C. H₂O uptake - osmosis (32.6, p. 698)

1. "Salts" are concentrated within root

a. root H₂O is thus at lower concentration than soil H₂O

2. H₂O enters root easily and moves "down" concentration gradient
3. H₂O can move inward through extracellular spaces between cell walls

IV. Water (mineral) transport to leaves : UP Xylem

A. There is a continuous column of H₂O in the xylem from soil to leaf.

*Water adheres to hydrophillic surfaces/substrates

B. Leaf anatomy and physiology revisited (32.7, p. 700)

1. Epidermis / Mesophyll / Stomata (guard cells) / Vascular bundle / Airy
2. very large, wet surface area inside leaf (film), H₂O is continuous to root

C. Cohesion - Tension Theory (32.7, p. 700)

1. H₂O molecules interact through hydrogen bonding (H^OH--OH₂)

- hydrogen bonding creates cohesion of water from root to leaf

2. Evaporation of water film in leaf interior high surface area

- as film gets thin, hydrogen bonding gets strained (stretched spring)

3. Hydrogen bond tension draws water up xylem

- requirement - high surface area within leaf - thin film
- requirement - water continuum to root

D. Regulation: Transpiration, Photosynthesis and Stomata

1. Transpiration - regulated evaporation from leaf surface
2. Photosynthesis requires H₂O and CO₂
3. Stomata (32.8, p. 703)

Guard cells

open in light - photopigments > K⁺ uptake
open in low CO₂ - CO₂ receptors > K⁺ uptake
close low H₂O - hormone regulated - abscisic acid
Mechanism - opening

Cytoplasmic increase in K⁺
Osmotic entry of H₂O
Cells swell - cell walls strain and torsion out - stoma opens

4. Leaves regulate Transpiration through stomata regulation

V. Transport AROUND Plant: Phloem - movement of biomolecules (sugars, amino acids, hormones)

A. Sieve Tube contents under positive pressure
B. Sucrose gradients - sources and sinks

1. sites of PS = sites of high sucrose
2. sites of low PS = sites of low sucrose

C. Sucrose loading (32.9, p. 706; 32.10, p. 707)

a. active transport sucrose into Companion Cells

- from photosynthetic palisade and spongy cells
- against concentration gradient
- ATP dependent

b. sucrose diffuses out into sieve tubes, creating high pressure
c. water drawn into sieve tubes from neighboring xylem by osmosis

D. Movement down pressure gradient

a. tissue of low PS - sucrose is actively transported out of sieve tubes
b. [sucrose]tissue > [sucrose]sieve tube, creating low pressure
c. water moves out of sieve tube into surrounding tissue by osmosis

E. Taking it all in - bulk fluid flow from area of high PS to any area of low PS

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