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BIO2202 Plant Physiology 1 Stress Physiology Lecture 1

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Title: BIO2202 Plant Physiology 1 Stress Physiology Lecture 1


1
BIO2202 Plant Physiology 1Stress Physiology -
Lecture 1
  • An Introduction to Stress

2
Lecture Outline
  • Definitions
  • Adaptation and Acclimation
  • Types of Stress
  • - Water stress

3
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.

4
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.

5
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

6
Types of Stress
  • Biotic stress
  • - herbivores, insects
  • - pathogens, parasites

7
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

8
The Physical (Abiotic) Environment
  • Influences the rate of plant growth
  • Affects the pattern of development
  • A major determinant of the geographical
    distribution of plants

9
Classification of Plant Types
  • Hydrophytes - live in or near water
  • Mesophytes - most land-dwelling plants
  • Xerophytes - plants which grow in arid
    environments

10
Xerophyte Strategies
  • Drought escape
  • - avoiders, complete life cycle during wet
    season
  • - desert ephemerals

11
Xerophyte Strategies
  • Drought tolerance
  • - dessication postponement high tissue ?
  • water savers
  • water storers
  • water spenders

12
Xerophyte Strategies
  • Drought tolerance
  • - dessication tolerance low tissue ?
  • dehydration endurers (Euxerophytes)

13
Drought Tolerance Strategies in Xerophytes
  • Altered leaf morphology
  • Leaf shedding/deciduous habit
  • Specialised root systems
  • Altered photosynthetic mechanisms
  • Salt secretion
  • Osmoregulation

14
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.
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