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