Polyamines as key regulatory players in plants under metal stress—A way for an enhanced tolerance

Abstract

Abstract Polyamine (PA) metabolism and functions have started to raise attention from plant scientists in the last years. PAs have been investigated for their involvement in plant cell signalling and protection, proving that alterations in their endogenous levels can affect plant growth, development and survival. The recognised roles of PAs in metal‐stressed plants are presented and discussed on a “case‐study” basis, for each metal. Bearing in mind that the contamination of soils by heavy metals (HMs) is a growing problem worldwide, it is important to find efficient mechanisms through which agricultural productivity and food quality are safeguarded in a scenario of increased pollution. Making cultivars more tolerant to HM‐stress, capable of detoxifying or accumulating them safely, is a goal that will most certainly benefit from researching the functions and applicability of PAs. To date, plant PAs have been recognised for their roles as membrane‐, protein‐ and nucleic acid‐stabilisers, as protectors of cellular integrity and photosynthetic machinery, as direct and indirect signalling agents, and as emerging members of the non‐enzymatic antioxidant system. Moreover, PAs are not only important in normal plant developmental processes but have also been suggested to induce stress priming, to act as epigenetic regulators of gene expression and to enhance the detoxification and vacuolar compartmentalization of HMs. Although the stress‐ameliorating effects of PAs have been widely studied for several abiotic stresses, not much is known regarding their effects on metal induced‐stress, except for Cd. This review summarises the available work on the effects of PAs in plants exposed to Cu, Cd, Fe, Mn, Cr, Ni, Hg, Al, Pb and Zn.