Stress Physiology

Just like every other living organism, plants are regularly exposed to adverse environmental conditions - water deficit, drought, cold, heat, salinity and air pollution - and stress physiology is the branch of plant science that studies how plants function under these conditions (Figure 15.31). Jacob Levitt first used the term 'biological stress' for plants in 1972, defining stress broadly as any change in environmental conditions that could adversely affect a plant's growth and development; the plant's actual reaction to that stress is separately termed strain. Strain itself comes in two forms: elastic biological strain is a temporary reaction that reverses once conditions improve (e.g. temporary wilting), while plastic biological strain is a permanent reaction the plant does not recover from (e.g. permanent wilting). Plants also differ in how they cope with stress overall: stress resistant (or stress tolerant) plants, such as mangroves, are simply not badly affected by the stress they face; stress enduring plants cannot cope directly and instead survive adverse periods by entering a dormant state; and stress escaping plants, such as short-lived desert ephemerals, avoid the problem altogether by completing their entire life cycle during the brief favourable window (e.g. seasonal rains) before the harsh season …