Response of Plant to Stress

Presented ByAbu Khairul Bashar

Roll No: 584; Session: 2011-2012Email: abukhairulbashar@gmail.com

Department of Environmental SciencesJahangirnagar University,

Savar, Dhaka-1342

Stress۞ Biological stress is not easily defined but it implies adverse

effects on an organism. Like all other living organisms, the plants are subjected to various environmental stresses such as water deficit and drought, cold, heat, salinity and air pollution etc.

۞ The concept of stress is associated with stress tolerance. Degree of tolerance differs with different plant species.

According to Levitt (1972), ``Stress is any change in environmental conditions that might reduce or adversely change plant’s growth and development. ``

According to Jones (1989)``Adverse force or influence that tends to inhibit normal systems from functioning. ``

Continuous…..

Types of Stress

Abiotic Stresses

Temperature (high / low) Water (high / low) Salt Radiation

Biotic Stresses

Fungi Bacteria Insects Herbivores Other plants

Flowchart

Plant Stress

۞ Plants can respond to stress in several ways. Plants may escape the effects of stress by completing their growth during less stressful periods or they may suffer injury if the stress is present and they cannot cope.

۞ Stress resistant plants can tolerate a particular stress. Many Plants have the capacity to resist stress through either stress avoidance or stress tolerance.

Stress Resistant or Stress Tolerance

Plants may become stress tolerant through-

◙ Adaptation: -Heritable modifications to increase fitness. -CAM plants’ physiological adaptations to low H2O environment.

◙ Acclimation: -Non heritable physiological and biochemical gene expression. -Cold-hardy plants’ adaptation to high H2O environment.

Stages of Response to Stress

1. Reception2. Transduction3. Response

CELLWALL

CYTOPLASM

   1   Reception     2    Transduction     3   Response

Receptor

Relay molecules

Activationof cellularresponses

Hormone orenvironmentalstimulus

Plasma membrane

Environmental Stresses to Which Plants may be Subjected

High Temperature (Heat) Low Temperature (Chilling, Freezing) Water Deficits (Drought, Low water potential) Salinity Excess water (Flooding, Anoxia) Chemical (Heavy metals, Air Pollutants) Radiation (Visible, Ultraviolet) Pathogens Competition

Respond of Plant at Different Parts

Water Stress

▲Water stress is a major abiotic stress. Induced by many environmental conditions.

▲Water stress may arise through either an excess of water or a water deficit. Water stress is primarily caused by a water deficit, such as a drought or high soil salinity.

▲Rate of duration influence the water stress response.

Water Stress and Water Availability

₪ Reduction in cell and leaf expansion.

₪ Reduction in photosynthesis.₪ Impact on Metabolism.₪ Effect on shoot and root

growth.

Effects of Water StressSmaller leavesLess light receptionLess photosynthesis

Temperature Stress

☼ Each plant has its unique set of temperature requirement for growth and development. There are two types of limits of temperature-upper limit and lower limit.

☼ Except in the relatively stable climates vary depending on the environment. Temperature may be of two kinds-

-High Temperature -Low Temperature

Gro

wth

afte

r 1 m

onth

RED has a greater stress tolerance than Blue

High T Low T

Comparison With Temperature

Continuous…

The effects of Low Temperature included the following –

A. Chilling StressB. Freezing Stress

Chilling Stress

› Chilling injury refers to an injury that is caused by a temperature drop to below 15°C but above the freezing point.

› Plasma membrane is the most common site for chilling injury.

› The consequences of this change may lead to cell leakage or disruption and loss of cell liquid.

Plant at Chilling Stress

Chilling Affects on Plants

Chilling injury causes several physiological dysfunctions to the plant including-

Disruption of the conversion of starch to sugars Decreased carbon dioxide exchange Reduction in net photosynthesis The destruction/degradation of chlorophyll

Freezing Stress

It freezes at about -2°C, depriving the plant of its source of water. It occurs by rapid freezing of cells to a  very low temperature.Freezing injury in plants can be from two sources:

1. Freezing of soil water, and; 2. Freezing of the fluids within the plant.

Plant at Freezing Stress

▲Desiccation or Burning of foliage.▲Freezing can rupture membranes.▲Extracellular ice can dehydrate protoplast▲Increase necrotic spots on leaves, stems or fruit of the plant.▲Reveal a dead or weakened root system.▲Increase transpirational water loss.

Freezing Affects on Plant

References

William G. Hopkins, 2002. Introduction to Plant Physiology, 2nd edition, John Wiley and Sons. Inc. New York.

Any Question?

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