BIO2202 Plant Physiology 1 Stress Physiology Lecture 1

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BIO2202 Plant Physiology 1Stress Physiology -
Lecture 1

• An Introduction to Stress

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Lecture Outline

• Definitions
• Adaptation and Acclimation
• Types of Stress
• - Water stress

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Definitions

• Stress
• - An external factor which exerts a
  disadvantageous effect on the organism.
• OR
• - Any change in environmental conditions which
  adversely alters plant growth or development
• Strain
• - The reduction in plant growth or function
  resulting from a stress.

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More Definitions.

• Adaptation to Stress
• - Genetically determined resistance acquired
  over generations by selection.
• - Heritable modifications in structure or
  function which increase the fitness of the plant
  in a stressful environment.

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More Definitions.

• Acclimation to Stress
• - An increase in the stress tolerance of an
  individual plant as a result of exposure to
  prior stress
• - Non-heritable physiological modifications
  made during the life of the individual plant
• NOTE The capacity to acclimate is genetically
  determined

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Types of Stress

• Biotic stress
• - herbivores, insects
• - pathogens, parasites

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Types of Stress

• Abiotic (edaphic climatic/atmospheric)
• - extremes of temperature (heat, chilling,
  freezing)
• - excess water (waterlogging, anoxia, flooding)
• - water stress (drought, low ?)
• - salinity
• - nutrient extremes
• - radiation (UV, high visible)
• - allochemicals (herbicides, pesticides,
  pollutants)
• - wind

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The Physical (Abiotic) Environment

• Influences the rate of plant growth
• Affects the pattern of development
• A major determinant of the geographical
  distribution of plants

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Classification of Plant Types

• Hydrophytes - live in or near water
• Mesophytes - most land-dwelling plants
• Xerophytes - plants which grow in arid
  environments

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Xerophyte Strategies

• Drought escape
• - avoiders, complete life cycle during wet
  season
• - desert ephemerals

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Xerophyte Strategies

• Drought tolerance
• - dessication postponement high tissue ?
• water savers
• water storers
• water spenders

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Xerophyte Strategies

• Drought tolerance
• - dessication tolerance low tissue ?
• dehydration endurers (Euxerophytes)

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Drought Tolerance Strategies in Xerophytes

• Altered leaf morphology
• Leaf shedding/deciduous habit
• Specialised root systems
• Altered photosynthetic mechanisms
• Salt secretion
• Osmoregulation

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Water Stress in Mesophytes

• Huge variations in tolerance and ability to
  acclimate.
• Subject of intense study due to economic
  importance.
• Can exhibit tolerance strategies similar to
  xerophytes to some extent.