What is Plant Stress?
Stress is an external factor that exerts disadvantageous influence on
the plant. Plants are frequently exposed to environmental stresses such as air
temperature, soil water content & soil mineral deficiencies.
Stress plays an important role in determining the effect of climate and
soil on plants and their modification in response.
WATER STRESS
Water stress is defined as any water content of a tissue or cell that is
below the highest water content exhibited at the most hydrated state.
EFFECT OF WATER STRESS AND MODIFICATION IN PLANTS
Water stress shows several effects on plant
·
Leaves
·
Roots
·
Stomata
·
Photosynthesis within chloroplast
·
Leaf energy
1. Effect of Water
Stress on Leaves
Leaf expansion is sensitive to water stress as it cause turgor reduction,
affects cell division of leaves and wilting of leaves.
Modifications
·
Decreased leaf area is an early adaptive response to
water deficit.
·
Small leaf area transpire less water and conserving a
limited water supply in the soil over a longer period.
2.
Effects of Water Stress on Roots
Root to shoot biomass ratio appears to be governed by a functional
balance between water uptake by the root and photosynthesis by the shoot. This
functional balance is shifted if water supply decreases.
Modifications
·
Water deficit
enhance root extension into deeper, moist soil.
3.
Effect of Water Stress on Stomata
·
Water control stomatal regulation.
·
Deficiency of water reduce turgidity and results in closing of
stomata.
· Closing of stomata may be Hydropassive or Hydroactive.
4.
Effect of Water Stress on Photosynthesis
Mild water stress little affects photosynthesis but severe conditions
inhibit it.
Modifications
·
Rate of photosynthesis can be maintain by the exposure
of stressed leaves to air containing high concentration of CO2.
5.
Effect of Water Stress on Plant Temperature
Water stress limits transpiration, the leaf heats up.
Modifications
·
Leaf orientation against heating during water stress
i.e.
·
Paraheliotropic movement
·
Diaheliotropic movement
·
Other modications includes
·
Hair on leaf surface
·
Reflective wax outside the cuticle.
STORAGE IN WATER STRESS
In the event of water stress plants show adaptations in form of
different storage compounds such as
a) Wax deposition on
leaves
Production of wax layer on leaves reduce water loss
from epidermis.
b)
Crassulacean Acid Metabolism
Plant adaptation in which stomata open at night and close during the
day.
Crassulacean Acid Metabolism (CAM) is very prevalent in succulent plants
like cacti.
c)
Osmotic Adjustment of Cells
Osmotic adjustment of cell maintain plant water balance as it cause
increase in solute content per cell that is independent of volume change that
result from loss of water.
