Hormesis in plant tissue culture

Hormesis or hormetic effect is characterized by a biphasic response caused by a stressor or stressor agent. The first phase of hormesis is stimulation at low or sublethal doses, whereas the second phase occurs through inhibition or death at high or lethal doses of the stressor. Both phases are represented using mathematical models in the form of dose-response curves. In plants, hormesis has morphological, physiological, biochemical and molecular effects. These effects act as response mechanisms of adjustment or coupling to the stressor. Adjustment or coupling mechanisms can be exploited in plant tissue culture (PTC) to increase or promote plant length, number of leaves, number of roots, biomass and secondary metabolites, or to induce or enhance morphogenesis in vitro. This review compiles recent findings on hormesis using PTC techniques and the mechanisms of response to different stressors. Stressor agents that present a hormetic dose response (stimulation, inhibition) include silver nanoparticles (50, 100 mg/L), arsenic (1.15, 50.15 mg/kg), multi-walled carbon nanotubes (50, 200 mg/L), 60Co gamma rays (20, 60 Gy), microplastics (0.01, 0.1 mg/L), and a magnetic field (65, 172 mT), among others. In addition, topics such as general plant hormetic response to abiotic stressors, physiological and biochemical aspects of hormesis, hormetic response to metals and nanomaterials, and other curious examples of hormesis are included. Hormesis could be considered as a novel strategy to improve growth and differentiation in different PTC areas and applications. It is suggested to document new cases of hormesis and carry out future studies to elucidate and understand the hormetic effect response mechanisms to different stressors through in vitro biological models.