Beneficial Role of Exogenous Spermidine on Nitrogen Metabolism in Tomato Seedlings Exposed to Saline-alkaline Stress

Abstract

<jats:p>We studied the effects of exogenous spermidine (Spd) on plant growth and nitrogen metabolism in two cultivars of tomato (<jats:italic>Solanum lycopersicum</jats:italic>) that have differential sensitivity to mixed salinity-alkalinity stress: ‘Jinpeng Chaoguan’ (salt-tolerant) and ‘Zhongza No. 9’ (salt-sensitive). Seedling growth of both tomato cultivars was inhibited by salinity-alkalinity stress, but Spd treatment alleviated the growth reduction to some extent, especially in ‘Zhongza No. 9’. Exogenous Spd may help reduce stress-induced increases in free amino acids, ammonium (NH<jats:sub>4</jats:sub><jats:sup>+</jats:sup>) contents, and NADH-dependent glutamate dehydrogenase (NADH-GDH) activities; depress stress-induced decreases in soluble protein and nitrate content; and depress nitrate reductase, nitrite reductase, glutamine synthetase (GS), NADH-dependent glutamate synthase (NADH-GOGAT), glutamate oxaloacetate transaminase (GOT), and glutamate pyruvate transaminase (GPT) activities, especially for ‘Zhongza No. 9’. Based on our results, we suggest that exogenous Spd promotes the assimilation of excess toxic NH<jats:sub>4</jats:sub><jats:sup>+</jats:sup> by coordinating and strengthening the synergistic action of NADH-GDH, GS/NADH-GOGAT, and transamination pathways, all during saline-alkaline stress. Subsequently, NH<jats:sub>4</jats:sub><jats:sup>+</jats:sup> and its related enzymes (GDH, GS, GOGAT, GOT, and GPT), in vivo, are maintained in a proper and balanced state to enable mitigation of stress-resulted damages. These results suggest that exogenous Spd treatment can relieve nitrogen metabolic disturbances caused by salinity-alkalinity stress and eventually promote plant growth.</jats:p>

Exogenous DCPTA Increases the Tolerance of Maize Seedlings to PEG-Simulated Drought by Regulating Nitrogen Metabolism-Related Enzymes

“…Previous studies have shown that drought stress can increase the NH 4 + content in bamboo [51] and tomato [46]. NH 4 + is produced by the NO 3 − assimilation and oxidation of glycine during the photorespiration process under stress conditions, and excessive accumulation of NH 4 + is detrimental to plants, as it can trigger protein extrusion and disturb cytosolic pH [7,52]. GS is responsible for glutamine synthesis in the NH 4 + assimilation process as the entry point of inorganic N into the organic form, and GOGAT is responsible for catalysing the transfer of the amide group of glutamine to 2-oxoglutarate, generating glutamate simultaneously [46].…”

Polyamines in conventional and organic vegetables exposed to exogenous ethylene

“…For humans, excessive intake of Cad can cause low blood pressure and heart rate, paralysis of the extremities and potentiation of toxicity of other amines (Moinard et al, 2005). However, analyzed plants were well below the limits of daily intake of these amines, which are essential for the development, growth and stress tolerance in all plants (Kalac & Krausova, 2005;Nishimura et al, 2006;Zhang et al, 2013a). In fact, foods of most concern are meat products, seafood, fermented products and cheeses (Kalac & Krausova, 2005).…”

“…According to Zhang et al (2013a), stress intensity and the levels of polyamines, as well as the specific mechanism of regulation of PAs, are very obscure and controversial. However, the protective role of Spd and Spm against salt stress is well documented in some plants.…”

“…), alkaloids and terpenes (Schmelz, Leclere, Carroll, Alborn, & Teal, 2007). Among these substances, polyamines (PAs) exert a protective effect against various types of injuries as they favor the stability of cell membranes (Bae et al, 2008;Zhang et al, 2013a).…”

“…Conversely, PAs can limit the growth of plants and their massive ingestion in the diet may become a risk factor for human health, even if they possess beneficial dose dependence (Moinard, Cynobera, & De Bandt, 2005;Zhang et al, 2013a;Zhang et al, 2013b). Research studies to determine the dose-response of these substances, both for food safety and for the elucidation of regulatory effects in plants, are still lacking.…”