Translocation of Photosynthate

Translocation of Photosynthate

Two Separate Conducting Tissues:

Xylem

tracheids

vessel elements

Phloem - photosynthate (photoassimilate)

sieve tube elements

companion cells (nucleus)

Dicot

Stem X-Section -Herbaceous Dicot

Phloem Tissue

Parenchyma

fibers

Phloem

Cytoplasmic connections

P-Proteins (slime)

Callus Plugs (carbohydrate)

Sieve Plate - Callose Plugs

Phloem Sap - Sugars * Sucrose C12H22O11

Glucose - some Lilies, Liliaceae

Mannitol & Sorbitol (sugar alcohols) - Rosaceae

Raffinose, Stachyose, Verbascose -Cucubitaceae

Chemical Interconversions

PCR Cycle – 1st hexose phosphate = fructose-6-phosphate

phosphoglucomutase

F-6-P G-6-P ------------------------------ G-1-P

G-1-P starting pt. for synthesis of sucrose, starch, cellulose

Chemical Interconversions

G-1-P starting pt. for synthesis of sucrose, starch, cellulose

UTP + G-1-P UDPG (uridine diglucophosphate) + P P

UDPG + F-6-P G-F-6-P (sucrose-6-phosphate)

G-F-6-P G-F (sucrose) + P

Carbon AllocationStarch (storage) Sugars (translocation)

Sugarbeets and Sugarcane - store sucrose

Chemical Interconversion

Starch Synthesis: glucose polymer – amylose 1-4 linkages Alpha amylopectin 1-4 and 1-6 Beta linkages

Build Up

ATP + G-1-P ADPG (adenosine diphosphoglucose) + P

ADGP + glucose G-G… + ADP

Chemical Interconversions

Cellulose

Most abundant carbohydrate on earth (cell walls)

Formed like starch (glucose donor is a different nucleotide sugar- GDPG)

Beta linkages between all glucose units

Seldom broken down in nature Microrganisms - cellulase

Phloem Sap - Non-Sugars Phytohormones -

Amino Acids (Glutamic and Aspartic Acids) & Other Organic Acids

Minerals - Anions (Phosphate, Sulfate, Chloride, etc.) & Cations (Potassium)

Aphids Use Stylus to Extract Phloem Sap

Carbon Distribution

Source --> Sink

Munch Pressure-Flow HypothesisE. Munch 1930

A Mechanism for Moving Phloem Sap from Source to Sink within the Plant

1. Sugars (solute) accumulate in leaves and other photosynthetic organs. SOURCE

2. Sugars are pumped into phloem of photosynthetic organ by active transport. LOADING

Munch Pressure-Flow HypothesisE. Munch 1930

A Mechanism for Moving Phloem Sap from Source to Sink within the Plant

1. Sugars (solute) accumulate in leaves and other photosynthetic organs. SOURCE

2. Sugars are pumped into phloem of photosynthetic organ by active transport. LOADING

Phloem Loading

Munch Pressure-Flow HypothesisE. Munch 1930

A Mechanism for Moving Phloem Sap from Source to Sink within the Plant

1. Sugars (solute) accumulate in leaves and other photosynthetic organs. SOURCE

2. Sugars are pumped into phloem of photosynthetic organ by active transport. LOADING

3. Loading of phloem causes phloem sap to take on water by osmosis. HYDROSTATIC PRESSURE

Munch Pressure-Flow HypothesisE. Munch 1930

A Mechanism for Moving Phloem Sap from Source to Sink within the Plant

1. Sugars (solutes) accumulate in leaves and other photosynthetic organs. SOURCE

2. Sugars are pumped into phloem of photosynthetic organ by active transport. LOADING

3. Loading of phloem causes phloem sap to take on water by osmosis. HYDROSTATIC PRESSURE

4. The Phloem sap is pushes through the seive tube column to a SINK area of low solute concentration. (root, bud, grain, bulb, etc.) Sap is pulled out by active transport or stored as starch. UNLOADING

5. Sap continues to flow toward the sink as long as sugars (solutes) do not accumulate in the phloem.

Phloem Unloading

Munch Pressure Flow Hypothesis is supported by the evidence.

Known rates of movement 100cm/hr., squash 290 cm/hr.

Living cells are necessary (active transport)

Direction of Phloem Sap Movement(Radioactive Feeding Techniques)

Distribution of Photosynthate

Sap moves in both directions (up & down) - in separate phloem ducts.

Very little tangential movement on maturre stem. Growth is decreased on defoliated side. Feed radioactive CO2 to one side - very little

radioactive photosynthate shows up on other side.

More tangential movement among young leaves.

Between Phloem and Xylem

Some exchange - mostly to remove mineral from senescent leaves (source to sink).

Factors Affecting the Translocation of Sap

Temperature Increased temperature – increased loading & unloading

optimum 20 - 30 degrees C

Chilling Sensitive Plants (most)

Chilling Tolerant Plants (beets) Can acclimate translocation of photosynthate to increasingly

cold conditions

Factors Affecting the Translocation of Sap

Light

In the dark root translocation of photosynthate is favored over stem translocation.

At least one study shows that the translocation of sap in the stem was increased by BLUE and RED light.

Factors Affecting the Translocation of Sap

Hormones Both cell division (cytokinins) and cell elongation (auxins)

creates sinks – absorbs sap.

Bud break Increased G A, decreased ABA

Development of Tissues of Transport and Translocation

Development of Tissues of Transport and Translocation

Development of Tissues of Transport and Translocation

Development of Tissues of Transport and Translocation

Consequences of Ambient Conditions on Tree Growth Rings

Dormant Woody Stem

If Aerobic:

1. Pyruvate (C3) is further broken down in the KREBS CITRIC ACID CYCLE (in mitochondrion)

2. NADH2s are used to build ATPs in the ELECTRON TRANSPORT CHAIN (ETC)

Krebs Citric Acid Cycle

Energy Budget

Glycolysis: 2 ATPs net gain from 1 glucose Anaerobic

Krebs Cycle & ETC: 36 ATPs net gain from 1 glucose

Aerobic: 38 ATPs

Cyanide Resistant RespirationMany plants have been discovered to have a branch point in the ETC.

After Coenzyme Q - Only 1 ATP produced - H2O2 produced

+ More heat produced + in plant tissues. + Fruit ripening + Rids excess NADH2. Krebs Cycle continues to produce intermediates.

Oxidative Pentose Phosphate Pathway

NADPH2 for PCR Cycle and Biosyntheses

Biosynthesis of Nucleic Acids, RuBP

Up to 20% of Glucose may use OPPP rather than Glycolysis.

Lipid Catabolism - Glycolate Cycle

Role of Respiration in Biosynthesis

Rate of Respiration

Aerobic Respiration in Green Plants

C6H12O6 + O2 --> CO2 + H2O

Respiratory Quotient RQ =

CO2 production: O2 consumption

Carbohydrates = 1.0, Organic Acids (highly oxidized) = 1.66, Lipids and Proteins (highly reduced) = .77

Respiratory Rate and Age

Photosynthesis and Respiration