Silicon‐mediated changes in polyamines participate in silicon‐induced salt tolerance in Sorghum bicolor L.

Abstract

Silicon (Si) is generally considered a beneficial element for the growth of higher plants, especially under stress conditions, but the mechanisms remain unclear. Here, we tested the hypothesis that Si improves salt tolerance through mediating important metabolism processes rather than acting as a mere mechanical barrier. Seedlings of sorghum (Sorghum bicolor L.) growing in hydroponic culture were treated with NaCl (100 mm) combined with or without Si (0.83 mm). The result showed that supplemental Si enhanced sorghum salt tolerance by decreasing Na(+) accumulation. Simultaneously, polyamine (PA) levels were increased and ethylene precursor (1-aminocyclopropane-1-carboxylic acid: ACC) concentrations were decreased. Several key PA synthesis genes were up-regulated by Si under salt stress. To further confirm the role of PA in Si-mediated salt tolerance, seedlings were exposed to spermidine (Spd) or a PA synthesis inhibitor (dicyclohexylammonium sulphate, DCHA) combined with salt and Si. Exogenous Spd showed similar effects as Si under salt stress whereas exogenous DCHA eliminated Si-enhanced salt tolerance and the beneficial effect of Si in decreasing Na(+) accumulation. These results indicate that PAs and ACC are involved in Si-induced salt tolerance in sorghum and provide evidence that Si plays an active role in mediating salt tolerance.

The controversies of silicon's role in plant biology

“…For example, Si supplementation has been claimed to influence many physiological parameters based on correlations with elevated polyamine levels (e.g. spermidine, spermine and putrescine) and reduced ethylene signaling in salt‐stressed sorghum (Yin et al ., ), but such observations are far from conclusive in terms of mechanistic evidence. Likewise, claims that Si alleviates K + deficiency‐induced leaf chlorosis by decreasing the accumulation of putrescine are unsubstantiated (Chen et al ., ).…”

The Variation Tendency of Polyamines Forms and Components of Polyamine Metabolism in Zoysiagrass (Zoysia japonica Steud.) to Salt Stress with Exogenous Spermidine Application

“…A recent study by Li et al (2016) demonstrated that application of 0.15 mM Spd alleviated the damage caused by salt stress in zoysia ( Zoysia japonica Steud.). Exogenous Spd application also enhanced the salt tolerance of sorghum ( Sorghum bicolor ) seedlings (Yin et al, 2016). Hu et al (2012) also found that exogenous application of 0.15 mM Spm reduced salt injury under salt stress in tomato.…”

Silicon-mediated Improvement in Plant Salinity Tolerance: The Role of Aquaporins

“…A complementary protective mechanism of plants growing under saline conditions is the synthesis and accumulation of different osmolytes and compatible solutes. Although this is dependent on the plant species, Si has been found to enhance the contents of proline (Tuna et al, 2008; Soylemezoglu et al, 2009; Siddiqui et al, 2014), soluble protein (Li et al, 2015), polyamines (Wang S. et al, 2015; Yin et al, 2016), glycine betaine, total free amino acids, soluble sugars, and phenolic compounds (Abbas et al, 2015). …”