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 C 12 H 22 O 11 Glucose - some Lilies, Liliaceae Mannitol & Sorbitol (sugar alcohols) - Rosaceae Raffinose, Stachyose, Verbascose - Cucubitaceae

Chemical Interconversions PCR Cycle – 1 st 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 Allocation Starch (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 Hypothesis E. 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 Hypothesis E. 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 Hypothesis E. 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 Hypothesis E. 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 CO 2 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 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

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. NADH 2 s 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 Respiration Many plants have been discovered to have a branch point in the ETC. After Coenzyme Q - Only 1 ATP produced - H 2 O 2 produced + More heat produced + in plant tissues. + Fruit ripening + Rids excess NADH 2. Krebs Cycle continues to produce intermediates.

Oxidative Pentose Phosphate Pathway NADPH 2 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 C 6 H 12 O 6 + O 2 --> CO 2 + H 2 O 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