Download Basic Principle in Plant Physiology

Factors Affecting Rates of
Respiration
• Temperature- For every 10 degree C
rise in temperature between 0-35 C the
rate of respiration increases 2X – 4X.
• Storage temperature for harvested plant
parts is often critical because these parts
continue to respire after harvest ( a
catabolic process) which causes a build
up of heat, and the breakdown of the
product.
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Factors Affecting Rates of
Respiration
• Most plants grow better when night
time temperatures are 5 degrees C
lower than day time temperatures.
• This is because lower night time
respiration reduces the use of
carbohydrates and allows more
carbohydrates to be stored or used
for growth.
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Factors Affecting Rates of
Respiration
• Oxygen concentration- Generally
speaking, lower oxygen level results in
the reduction of respiration.
• Controlled atmosphere (CA) storage in
which oxygen is decreased is useful in
storage of fruits and vegetables
because of lower respiration rates.
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Factors Affecting Rates of
Respiration
• Soil conditions- Compacted and/or
wet soil conditions result in low oxygen
in the root zone and reduced root
respiration.
• Consequently, roots don’t function well
in supplying mineral nutrients
essential for the activity of respiratory
enzymes which decreases overall
respiration.
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Factors Affecting Rates of
Respiration
• Light- Lower light intensities result in
lower respiration rates.
– Lower photosynthesis rates in low light
supply fewer carbohydrates essential for
respiration.
• Plant growth- As a plant grows it
depends on energy to be supplied by
respiration.
– The more growth that is occurring, the
higher the respiration rate must be.
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Summary of Respiration
• Aerobic Respiration
–
–
–
–
Glycolysis
Transition Rx.
Kreb’s Cycle
Electron Transport Chain
• Anaerobic Respiration
– Pyruvate 
• Lactic Acid
• Mixed Acids
• Alcohol + CO2
– Recycle NADH
– 2 ATP / Glucose
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Amino Acid Catabolism
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Amino Acids
• Building blocks for polymers called proteins
• Contain an amino group, –NH2, and a carboxylic
acid, –COOH
• Can form zwitterions: have both positively
charged and negatively charged groups on same
molecule
• 20 required for humans
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Peptide Bond
• Connect amino acids from carboxylic acid to
amino group
• Produce amide linkage: -CONH• Holds all proteins together
• Indicate proteins by 3-letter abbreviation
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Sequence of Amino Acids
• Amino acids need to be in correct order for
protein to function correctly
• Similar to forming sentences out of words
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Transaminase enzymes (aminotransferases)
Catalyze the reversible transfer of an
amino group between two a-keto acids.
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Example of a Transaminase reaction:
Aspartate donates its amino group, becoming the aketo acid oxaloacetate.
 a-Ketoglutarate accepts the amino group, becoming
the amino acid glutamate.
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In another example, alanine becomes pyruvate as the
amino group is transferred to a-ketoglutarate.
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Essential amino acids must be consumed in the diet.
Mammalian cells lack enzymes to synthesize their carbon
skeletons (a-keto acids). These include:
Isoleucine, leucine, & valine
Lysine
Threonine
Tryptophan
Phenylalanine (Tyr can be made from Phe.)
Methionine (Cys can be made from Met.)
Histidine (Essential for infants.)
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Amino Acid Metabolism
•Metabolism of the 20 common amino acids is
considered from the origins and fates of their:
(1) Nitrogen atoms
(2) Carbon skeletons
•For mammals:
Essential amino acids must be obtained
from diet
Nonessential amino acids - can be
synthesized
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The Nitrogen Cycle and Nitrogen
Fixation
• Nitrogen is needed for amino acids,
nucleotides
• Atmospheric N2 is the ultimate source of
biological nitrogen
• Nitrogen fixation: a few bacteria possess
nitrogenase which can reduce N2 to
ammonia
• Nitrogen is recycled in nature through the
nitrogen cycle
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Fig 17.1 The Nitrogen cycle
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Nitrogenase
• An enzyme present in Rhizobium bacteria
that live in root nodules of leguminous
plants
• Some free-living soil and aquatic bacteria
also possess nitrogenase
• Nitrogenase reaction:
N2 + 8 H+ + 8 e- + 16 ATP
2 NH3 + H2 + 16 ADP + 16 Pi
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Assimilation of Ammonia
• Ammonia generated from N2 is assimilated
into low molecular weight metabolites such
as glutamate or glutamine
• At pH 7 ammonium ion predominates (NH4+)
• At enzyme reactive centers unprotonated
NH3 is the nucleophilic reactive species
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A. Ammonia Is Incorporated into Glutamate
• Reductive amination of a-ketoglutarate by
glutamate dehydrogenase occurs in plants,
animals and microorganisms
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Glutamine Is a Nitrogen Carrier in Many
Biosynthetic Reactions
• A second important route in assimilation of
ammonia is via glutamine synthetase
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Glutamate synthase transfers a
nitrogen to a-ketoglutarate
Prokaryotes & plants
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Alternate amino acid production
in prokaryotes
Especially used if [NH3] is low. Km of Gln
synthetase lower than Km of Glu dehydrogenase.
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The First Step in Amino Acid Degradation is the Removal of
Nitrogen
•Amino acids released from protein turnover can be resynthesized into
proteins.
•Excess amino acids are degraded into specific compounds that can be
used in other
metabolic pathways.
•This process begins with the removal of the amino group, which can be
converted to
urea and excreted.
•The a-ketoids that remain are metabolized so that their carbon
skeletons can enter
glycolysis, gluconeogenesis, or the TCA cycle.
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The Biosynthesis of Amino Acids
•Amino acids are the building blocks of proteins and the nitrogen
source of many
other important molecules including nucleotides, neurotransmitters,
and prosthetic
groups such as porphyrins.
•Ammonia is the source of all nitrogen for all of the amino acids.
•The carbon backbones come from the glycolytic pathway, the pentose
phosphate
pathway, and/or the TCA cycle.
•Amino acid biosynthesis is feedback regulated to ensure that all
amino acids are
maintained in sufficient amounts for protein synthesis and other
processes.
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Summary of Protein and Amino Acid Degradation
•Proteins are degraded to amino acids.
•Protein turnover is tightly regulated.
•The first step in amino acid degradation is the removal
of nitrogen.
•Ammonium ion is converted into urea in most terrestrial
vertebrates.
•Carbon atoms of degraded amino acids emerge as major
metabolic intermediates.
•Inborn errors of metabolism can disrupt amino acid
degradation.
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Summary of Amino Acid Biosynthesis
•Microorganisms use ATP and a powerful reductant to reduce
atmospheric nitrogen to ammonia.
•Amino acids are made from intermediates of the TCA cycle
and other major pathways.
•Amino acid metabolism is regulated by feedback inhibition.
•Amino acids are precursors of many molecules.
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Overview of Nucleotide Biosynthesis
•Nucleotides serve as active precursors of nucleic acids.
•ATP is the universal currency of energy.
•Nucleotide derivatives such as UDP-glucose participate in
bioynthetic processes.
•Nucleotides are essential components of signal transduction
pathways.
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Two Classes of Pathways for the Synthesis
of Nucleotides.
•In the salvage pathway, a base is attached
to a ribose, activated in the form of 5phosphoribosyl-1-pyrophosphate (PRPP).
•In de novo synthesis, the base itself is
synthesized from simpler starting materials,
including amino acids.
•ATP hydrolysis is necessary for de novo
synthesis.
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Summary of Nucleotide Biosynthesis
•In de novo synthesis, the pyrimidine ring is assembled from
bicarbonate, aspartate, and glutamine.
•Purine bases can be synthesized de novo or recycled by salvage
pathways.
•Deoxyribonucleotides are synthesized by the reduction of
ribonucleotides.
•Key steps in nucleotide biosynthesis are feeback regulated.
•NAD+, FAD, and Coenzyme A are formed from ATP.
•Disruptions in nucleotide metabolism can cause pathological
conditions.
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