Physiological roles and signaling of polyamines in plants under stressed conditions

Adverse environmental conditions result in the loss of the yield potential. Thus, the research of plant stress mechanism and its control is one of the most important scientific fields to date. With the aim of plant stress reduction much attention is paid to physiologically active substances with potential applications in agriculture. One of the classes of plant bioregulators are polyamines (PAs). PAs are organic polymeric compounds present in all living organisms and implicated in a vast range of biological functions. The measurement of endogenous PAs levels and the activities of their metabolic enzymes, transgenic methods, and exogenous applications have been used to study their physiological functions in higher plants. A large body of evidence demonstrated that PAs participate in many aspects of plant growth and development. They are involved in cell division, embryogenesis, fruit development, dormancy termination, regulation of aging, and response to adverse environmental conditions. Studies have reported increased levels of PAs under stress conditions (temperature, drought, salt, heavy metals, etc.). Thus, they are suggested to be used as the metabolic markers for monitoring the impact of environmental stress on the metabolic status of live plants. The increased accumulation of PAs under stress conditions is the result of their biosynthesis, catabolism, and transport regulation. The manipulation of PAs contents improves environmental stress tolerance. Thus, various efforts are taken to use exogenous PAs and transgenic approaches to enhance plant stress tolerance and crop productivity. Much effort has been done on various aspects of fruits, vegetables, and ornamental crops using exogenous polyamines. Nevertheless, the role of PAs to solve agricultural issues has been widely studied; still a lot of research is needed to understand the phenomenon of their action.