1. BIO2202 Plant Physiology 1 Stress 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.