Lecture 11 ABSORPTION, TRANSLOCATION,ASSIMILATION AND RESPIRATION IN PLANTS

Absorption, Translocation and Assimilation in Plants  Absorption and Conduction of Water  Absorption and Transport of Mineral Nutrients  Translocation of Sugars

Water Absorbed by roots and distributed to all parts of plant; Some plants may be 200 ft tall ( requires much energy) roots may be 100 ft deep (300 feet total) What is the power source for this work? Must be continuous water connection in xylem Molecule to molecule (cohesion) From soil to leaf, fruits, flowers

Water Water does not move alone, carries nutrients for plant Nitrates  Used for protein Phosphates  Used to make ATP Magnesium  Part of chlorophyll molecule

Water Water absorbed in large quantities by plants Several hundred gallons/plant in some species Must absorb water to obtain minerals Water lost from (or exits) plant through Transpiration Exits through stomates

Dicot leaf structure

Location and structure of stoma

Transpiration Upward pull of water is started by evaporation of molecules from outer surface of mesophyll cells: Mesophyll cells become water deficient and must be refilled from adjacent cells Water passes from “wetter” plant cells to “drier” cells and forms an unbroken water chain (cohesion) from the outer surface of leaves to the roots in contact with wet soil Vapor pressure (water content) difference exists between root surface cells and surrounding soil moisture

Mineral Nutrients Minerals must be absorbed along with water to be used by plant Initially, plant nutrients come from the seed, until used up. - subsequent nutrients are obtained by plant roots from surrounding soil.

Mineral Nutrients  Large amount of energy required for root absorption of water and minerals What is the source of this energy?  Starches and sugars broken down by respiration What molecule is necessary for respiration?

Mineral Nutrients  Oxygen This is reason for poor performance of roots in waterlogged soils Soil aeration is very important  Root concentration of soil nutrients is very high Additional absorption is very difficult

Translocation of Sugars The movement of photosynthetic sugars throughout the plant is primarily through phloem  Movement is mostly downward in the plant with some movement laterally  Most translocated sugar is sucrose (disaccharide) Glucose + fructose (monosaccharide)

Be sure and know the difference between two words that sound a lot alike: Transpiration and, Translocation

Respiration and Carbohydrate Breakdown

 Factors Affecting Plant Respiration  Respiration Pathways  Electron Transport  Absorption, Translocation and Assimilation of Water

Plant Respiration Stepwise release of energy captured and stored by photosynthesis  Carbohydrates produced in photosynthesis are reconverted to CO 2, water and energy  Respiration energy is source for all life processes  This reaction does not occur all at once, but is a series of subreactions and cycles  Each step in a reaction is catalized by an enzyme

Enzymes – Protein Catalystes Enzymes – are composed of proteins (organic catlystes) that assist in making a chemical reaction go faster Enzymes are affected by the same factors that affect proteins Heat – as temperature increase chemical reactions go faster until a enzyme becomes denatured (60 C; 30 minutes) Salting out – as salt concentration increases, available water to suspend enzymes decreases. Charges on the enzyme become neutralized and they “fall” out of solution.

Enzymes - con’t Heavy Metals – certain heavy metals like (e.g. lead, mercury, cyanide, cadmium) can directly denature an enzyme Inhibitors – certain substances can act as inhibitors of enzymes

Overall Reaction: C 6 H 12 O 6 + 6H 2 O + O 2  6CO H 2 O + energy Glycolysis TCA Cycle Electron transport system

Factors Affecting Respiration  Temperature  Rate increases 2 – 4 times for each 10° rise between 32° and 95° F  Stored plant materials (seeds, fruit) will respire and degrade if not cool stored, specific for each crop  Best temp for ideal growth is night temp 5 - 9° F cooler than day temp

Factors Affecting Respiration  Oxygen concentration  Respiration declines as oxygen concentration decreases  Soil conditions  Waterlogged, compacted soils lack oxygen, reduces root respiration  Can cause reduced uptake of minerals and vice versa  Light  Low light intensities = low respiration because of low photosynthetic rates

Factors Affecting Respiration  Plant growth  Leaves function as both source (photosynthesis) and sink (respiration) and continues to increase as leaf grows, then peaks and both processes begin to decline  Respiration energy used for: Growth and metabolism Protein degradation and resynthesizing maintenance

Respiration Pathways  A sugar molecule is degraded by a series of reactions, starting with: 1) Glycolysis – each molecule of glucose yields 2 molecules of pyruvic acid & 4 molecules of ATP 2) TCA Cycle – pyruvic acid from glycolysis is degraded in a stepwise manner. Yield is CO 2 and H 2 O electron acceptors to enter electron transport system 3) Electron Transport System – series of oxidation-reductions in which electron acceptors from TCA Cycle and ADP combine to produce ATP and NADPH the energy sources of all life

Structure of an ATP molecule

Glycolysis

Alcoholic Fermentation Beer/Wine Making Glycolysis Citric Acid TO Aerobic Respiration Anaerobic Respiration

Lactic Acid Fermentation Pickle Making

TCA (tricarboxylic acid cycle) Citric Acid Cycle

Terminal Oxidation Pathway

Balance Sheet 1 glucose molecule = 38 ATP molecules 2 ATP (net) from glycolysis & 36 from T. O. Sun’s energy  carbohydrates (respiration)  chemical energy

Take Home Message Glycolysis is the first step in any respiration (anaerobic or aerobic) leading to the end product PYRUVATE Aerobic repiration goes through glycolysis, TCA and TO (38 ATP gained), O 2 required, CO 2 and H 2 O released. Anaerobic repiration goes through glycolysis and then to a final product (2 ATP gained), no O 2 required, CO 2 released