Analysis of interactions of nitric oxide and polyamine undercadmium stress in wheat

Abstract

Introduction Cadmium (Cd), which is a highly toxic trace element, enters the environment mainly from industrial processes and phosphate fertilisers. It reaches high levels in agricultural soils and is easily assimilated by plants. Taken up excessively by plants, Cd induces various visible symptoms of phytotoxicity, such as leaf roll, chlorosis and necrosis, growth retardation, browning of root tips, and finally death (Tran and Popova, 2013).Nitric oxide (NO) is a key signalling molecule that mediates various physiological functions and defence responses against abiotic and biotic stresses in plants. These functions include regulation of root development (Kolbert et al., 2008), senescence (Corpas et al., 2004), and adaptive responses to abiotic stresses like drought, heat, chilling, and high salinity, and defence responses against biotic stresses (Leitner et al., 2009;Wimalasekera et al., 2011). NO is also known as an intermediate signalling molecule in cytokinin, abscisic acid (Garcia-Mata and Lamattina, 2002), auxin (Kolbert et al., 2008), and polyamine (PA) (Tun et al., 2006) signalling. Sodium nitroprusside (SNP) is a "spontaneous" NO donor by releasing NO upon dissolution in aqueous solvents. 2-(4-Carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO) is a NO specific scavenger and widely used to abolish NO accumulation in plants.Being nitrogenous growth regulators, PAs are present ubiquitously in all living cells, have low molecular weight, and are polycationic. The most common free PAs in plants are spermidine (Spd, a triamine), spermine (Spm, a tetramine), and their obligate precursor putrescine (Put, a diamine), which plays a pivotal role in the regulation of plant developmental and physiological processes (Kusano et al., 2007). Due to their polycationic nature at physiological pH levels, PAs are able to interact with proteins, nucleic acids, membrane phospholipids, and cell wall constituents by either activating or stabilising these molecules. PAs are related to plant response under different abiotic stress conditions including low pH (Young and Galston, 1983), temperature (