HOW TO DEFINE THE WORD "STRESS"

HOW TO DEFINE THE WORD "STRESS"

    • In 1972, Jacob Levitt proposed a definition of biological stress derived from physical stress. Physical stress is any force applied to an object (ex: a steel bar); strain is the change in the object dimension caused by the stress.
    • Levitt suggested that biological stress is any change in environmental conditions that might reduce or adversely change plants growth or development (its normal function); biological strain is the reduced or changed functions.
    • Any change in environmental conditions that results in plant response less than the optimum might be considered stressful. Considering a plant suddenly subjected to reduced light levels. Since photosynthesis is immediately reduced, applying Levitt’s definition we say that the reduced light levels are the stress and reduced photosynthesis is strain.
    • Levitt went on to define elastic biological strain as those change in an organism’s function that returns to the optimal level when conditions return to those best suited to the organism studied (i.e., when biological stress has been removed). If the functions don’t returns to normal the organism is said to exhibit plastic biological strain.
    • In general, plant physiologist have emphasized in their studies such as plastic strains as those caused by the stresses of frost, high temperature, limited water, or high salt concentration and elastic strains in plants such as photosynthesis.
    • Levitt (1972) listed some other definitions. He suggested that we should distinguish between avoidance and tolerance (hardiness) to any given stress factors.
    • In avoidance, the organism responds by somehow reducing the impact of the stress factor. Ex: a plant in the desert might avoid the dry soil by extending its roots down to the water table.
    • If plant develops tolerance, on the other hand it simply tolerates or endures the adverse environment. Crosote bush is good example of a desert plant that is tolerant towards the drought. It simple dries out but scurvies anyway; it tolerate or endures the dryness of its protoplasm.


Last modified: Friday, 9 September 2011, 4:07 AM