Plant Stress Physiology

Energy is an absolute requirement for the maintenance of structural organization during the lifetime of an organism. The maintenance of such complex order over time requires a constant input of energy. This results to a constant flow of energy through all biological organisms, which provides the dynamic driving force for the performance of important maintenance processes such as cellular biosynthesis and transport to maintain its characteristic structure and organization as well as the capacity to replicate and grow. The maintenance of a steady-state results to homeostasis, the meta-stable condition of organisms. Any change in the surrounding environment of an organsim may disrupt its homeostasis.When environmental factors cause the modulation of homeostasis, the response may be defined as biological stress.Thus, it follows that plant stress can be defined as the adverse effect on the physiology of a plant, which is induced upon a sudden transition from some optimal environmental condition, where homeostasis is maintained, to a suboptimal condition, which disrupts the initial homeostatic state. Plant stress is considered a relative term because the experimental design to assess the impact of a stress always involves the measurement of a physiological phenomenon in a plant species under a suboptimal, stress condition compared to the measurement of the same physiological phenomenon in the same plant species under optimal conditions. Plant stress responses describe the suite of molecular and cellular processes that are triggered when a plant detects some form of stress. Stresses can be abiotic, such as drought or excess light, or biotic, such as herbivores or pathogens. The current concept of stress in plants has been well developed over the past 60 years. Any unfavorable condition or substance that affects or blocks a plant’s metabolism, growth, or development is regarded as stress. Vegetation stress can be induced by various natural and anthropogenic stress factors. It must be noted that one has to differentiate between short-term and long-term stress effects as well as between low-stress events that can be partially compensated for by acclimation, adaptation, and repair mechanisms, on the one hand, and strong stress or chronic stress events causing considerable damage that may eventually lead tofficell and plant death. In this textbook, some essential stress syndrome responses of plants are summarized in a unifying stress concept. The major abiotic, biotic, and anthropogenic stressors are explained. Some stress tolerance mechanisms are mentioned. Stress conditions and stress-induced damage in plants have so far been detected using the classical ecophysiological field methods as well as point data measurements of particular chlorophyll fluorescence parameters and of reflectance spectra. The novel laser-induced high-resolution fluorescence imaging technique, which integrates chlorophyll and blue-green fluorescence, marks a new standard in the detection of stress in plants.