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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.
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Translocation of Photosynthate Two Separate Conducting Tissues: Xylem tracheids vessel elements Phloem - photosynthate (photoassimilate) sieve tube elements companion cells (nucleus)
Phloem Tissue Parenchyma fibers
Phloem Cytoplasmic connections P-Proteins (slime) Callus Plugs (carbohydrate)
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)
Carbon Distribution • Source --> Sink
Munch Pressure-Flow HypothesisE. Munch 1930A 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 1930A 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 1930A 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 1930A 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.
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
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)
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.
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