Abstract
Polyamine (PA) catabolic processes are performed by copper-containing amine oxidases (CuAOs) and flavin-containing PA oxidases (PAOs). So far, several CuAOs and PAOs have been identified in many plant species. These enzymes exhibit different subcellular localization, substrate specificity, and functional diversity. Since PAs are involved in numerous physiological processes, considerable efforts have been made to explore the functions of plant CuAOs and PAOs during the recent decades. The stress signal transduction pathways usually lead to increase of the intracellular PA levels, which are apoplastically secreted and oxidized by CuAOs and PAOs, with parallel production of hydrogen peroxide (H2O2). Depending on the levels of the generated H2O2, high or low, respectively, either programmed cell death (PCD) occurs or H2O2 is efficiently scavenged by enzymatic/nonenzymatic antioxidant factors that help plants coping with abiotic stress, recruiting different defense mechanisms, as compared to biotic stress. Amine and PA oxidases act further as PA back-converters in peroxisomes, also generating H2O2, possibly by activating Ca2+ permeable channels. Here, the new research data are discussed on the interconnection of PA catabolism with the derived H2O2, together with their signaling roles in developmental processes, such as fruit ripening, senescence, and biotic/abiotic stress reactions, in an effort to elucidate the mechanisms involved in crop adaptation/survival to adverse environmental conditions and to pathogenic infections.
Highlights
Polyamines (PAs) are small aliphatic amines present in all living cells
AtPAO5 is classified as a cytosolic Spm oxidase/dehydrogenase protein undergoing proteasomal control (Ahou et al, 2014), that controls Arabidopsis growth via t-Spm oxidase activity (Kim et al, 2014; Liu et al, 2014d), while the rice OsPAO1 is a functional ortholog of AtPAO5 (Liu et al, 2014d) and the rice OsPAO7 is involved in lignin synthesis in anther cell walls (Liu et al, 2014c)
Many attempts have been made to investigate the roles of PA catabolism in plant growth, development, fruit ripening, and responses to biotic and abiotic stresses
Summary
Polyamines (PAs) are small aliphatic amines present in all living cells. For more than 100 years in biology, they were misunderstood as “ptomaine or food poisoning” substances by toxicologists (Cohen et al, 1981). Exogenous PA application enhanced plant tolerance/resistance to several abiotic stress conditions, such as salinity, drought, water logging/flooding, osmotic stress, heavy metals, and extreme temperatures (Liu et al, 2006, 2015; Moschou et al, 2008c, 2012; Paschalidis et al, 2009a; Toumi et al, 2010; Moschou and Roubelakis-Angelakis, 2014; Gupta et al, 2016; Handa et al, 2018; Nguyen et al, 2018; Tiburcio and Alcazar, 2018; Pal et al, 2019; Yin et al, 2019). The present approach might help in unraveling the role/use of the PA catabolic pathway in plants as a focus area for innovative stress resistance/tolerance approaches
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