Exogenous spermine-induced expression of SISPMS gene improves salinity-alkalinity stress tolerance by regulating the antioxidant enzyme system and ion homeostasis in tomato

The study tested the function of exogenous spermine (Spm) in resisting salinity-alkalinity stress in tomato seedlings and found that tomato Spm synthase gene (SISPMS) was involved in this regulation. The tomato seedlings cultivated in normal conditions or salinity-alkalinity conditions were irrigated with 100 ml one strength Hoagland nutrient solution 100 ml mixed solution (5 ml 300 mmol/L NaCl, 45 ml 300 mmol/L Na2SO4, 45 ml 300 mmol/L NaHCOg, and 5 ml 300 mmol/L Na2CO3 (pH = 8.90)) every 2 days, respectively. The 0.5 mM Spm pretreatment improved superoxide dismutase (SOD; EC 1.15.1.1) activity, catalase (CAT; EC 1.11.1.6) activity, ascorbate peroxidase (APX; EC 1.11.1.11) activity, and glutathione reductase (GR; EC 1.6.4.2) activity and decreased endogenous hydrogen peroxide (H2O2) content, malondialdehyde (MDA) content, and relative electrical conductivity (REC) in tomato leaves. Na+ content declined and K+ concentration rose in tomato seedlings when pre-treated with Spm. However the results showed that under salinity-alkalinity stress, silencing of SISPMS with virus-induced gene silencing had lower antioxidant enzyme activities and higher Na+ content and lower K+ content than normal tomato seedlings, meaning that they had low salinity-alkalinity tolerance. Exogenous Spm could not reconstruct the tolerance to salinity-alkalinity stress in SISPMS gene-silencing tomato seedlings. Taken together, exogenous Spm could induce the expression level of SISPMS, which regulated the antioxidant enzyme system and ion homeostasis in tomato seedlings living in salinity-alkalinity environment, thereby improving the ability of tomato seedlings to resist salinity-alkalinity stress.