Polyamines and metal stress tolerance in plants

Abstract

Anthropogenic activities involving industrialization, urbanization, changes in land use, and excessive use of chemical fertilizers have contributed significantly to the accumulation of heavy metals (HMs) and metalloids in agricultural soils, affecting yield production and representing a latent risk to human health. Plants produce diverse molecules to activate the response to abiotic stress, among them are polyamines (PAs) which are derived from amino acids by decarboxylation. PAs are widely distributed in all kingdoms of life. Putrescine [NH2(CH2)4NH2], spermidine [NH2(CH2)4NH(CH2)3NH2], and spermine [NH2(CH2)3NH(CH2)4NH(CH2)3NH2] are the most abundant PAs in all plant life cycles, whereas cadaverine [(CH2)5(NH2)2] and thermospermine [C10H26N4] are induced by specific stimulus. These amines promote growth even under adverse conditions, including HM stress by turning on the expression of abiotic stress-responsive genes and by modulating the activity of diverse metabolic enzymes. In this chapter, we discuss the different findings pointing to the contribution of PAs in the tolerance of plants to stress by HMs such as cadmium, aluminum, arsenic, zinc, and copper, and the interaction of PAs with other hormones in regulating the stress response. Up to now, there is still debate on the specific role of each type of PA in the plant HM response, the evidence discussed herein converges on the idea that one of the main protective effects of PAs is in maintaining the plant redox balance.