Abstract
Hydrogen sulfide (H2S) plays a crucial role in regulating chilling tolerance. However, the role of hydrogen peroxide (H2O2) and auxin in H2S-induced signal transduction in the chilling stress response of plants was unclear. In this study, 1.0 mM exogenous H2O2 and 75 μM indole-3-acetic acid (IAA) significantly improved the chilling tolerance of cucumber seedlings, as demonstrated by the mild plant chilling injury symptoms, lower chilling injury index (CI), electrolyte leakage (EL), and malondialdehyde content (MDA) as well as higher levels of photosynthesis and cold-responsive genes under chilling stress. IAA-induced chilling tolerance was weakened by N, N′-dimethylthiourea (DMTU, a scavenger of H2O2), but the polar transport inhibitor of IAA (1-naphthylphthalamic acid, NPA) did not affect H2O2-induced mitigation of chilling stress. IAA significantly enhanced endogenous H2O2 synthesis, but H2O2 had minimal effects on endogenous IAA content in cucumber seedlings. In addition, the H2O2 scavenger DMTU, inhibitor of H2O2 synthesis (diphenyleneiodonium chloride, DPI), and IAA polar transport inhibitor NPA reduced H2S-induced chilling tolerance. Sodium hydrosulfide (NaHS) increased H2O2 and IAA levels, flavin monooxygenase (FMO) activity, and respiratory burst oxidase homolog (RBOH1) and FMO-like protein (YUCCA2) mRNA levels in cucumber seedlings. DMTU, DPI, and NPA diminished NaHS-induced H2O2 production, but DMTU and DPI did not affect IAA levels induced by NaHS during chilling stress. Taken together, the present data indicate that H2O2 as a downstream signal of IAA mediates H2S-induced chilling tolerance in cucumber seedlings.
Highlights
Cucumbers (Cucumis sativus L.) are typical light-loving and cold-sensitive plants, but they are mainly cultivated in solar greenhouses in northern China
To explore the effect of exogenous H2 O2 on chilling tolerance in cucumber, we determined the maximum photochemical efficiency of PSII (Fv /Fm ), actual photochemical efficiency of PSII (ΦPSII ), chilling injury index (CI), electrolyte leakage (EL), and photosynthetic rate (Pn ) of cucumber seedlings, which were pretreated with different concentrations of H2 O2 after exposure to 8/5 ◦ C for 24–72 h
The Fv /Fm, ΦPSII, and Pn of H2 O2 -treated seedlings were much higher, and the CI and EL were much lower than 0 mM H2 O2 (H2 O) treatments
Summary
Cucumbers (Cucumis sativus L.) are typical light-loving and cold-sensitive plants, but they are mainly cultivated in solar greenhouses in northern China. Chilling is considered as a crucial limitation to growth and yield in cucumber production. Hydrogen sulfide (H2 S) is a novel gaseous signaling molecule that plays an important role in regulating plant growth and development and defense responses to various abiotic stresses. Previous studies revealed that H2 S upregulated the expression levels of mitogen-activated protein kinase (MAPK) and was involved in the upregulation of MAPK gene expression caused by cold stress [2]. The exogenous fumigation of H2 S or application of sodium hydrosulfide (NaHS, the H2 S donor), can relieve multiple abiotic stresses, such as chilling, heat, salinity, drought, hypoxia, and heavy metal toxicity [3]
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