Thermodynamics of Abiotic Stress and Stress Tolerance of Cultivated Plants

Plants, as living systems, depend simultaneously on their internal status and their surroundings. Changes in plants’ surroundings, generated by different environmen‐ tal factors (abiotic stress), could perturb existing homeostasis, thus imposing stress. Abiotic stress includes heat, cold, freezing, flooding, drought (refers to water deficit), weak or strong light, oxygen deficiency or sufficiency, increased UV or other ionising rays, high salinity or acidity of the soil, deficiency or sufficiency of mineral elements, and presence of pollutants (xenobiotics). The effect of each abiotic factor depends on its severity, duration, developmental stage of the plant and its susceptibility to stress. During stress, requirements for energy increase (with increased intensity of respiration —domination of exergonic processes) as well as entropy. Variations in environmen‐ tal factors could push the plant’s metabolism out of homeostasis. In order to reestab‐ lish it, smaller or higher amounts of energy are required. The intention to increase the yield (grain or biomass production) of cultivated plants requires additional energy for successful completion of their life cycle, which makes them especially susceptible to stressful environments. From this point, the necessity to develop tolerant genotypes, which require less energy for maintaining homeostasis, arises.