H2O2 mediates ALA-induced glutathione and ascorbate accumulation in the perception and resistance to oxidative stress in Solanum lycopersicum at low temperatures

Abstract

Background: Low temperature is a crucial factor influencing plant growth and development. The chlorophyll precursor, 5-aminolevulinic acid (ALA) is widely used to improve plant cold tolerance. However, the interaction between H₂O₂ and cellular redox signaling involved in ALA-induced resistance to low temperature stress in plants remains largely unknown. Here, the roles of ALA in perceiving and regulating low temperature-induced oxidative stress in tomato plants, together with the roles of H₂O₂ and cellular redox states, were characterized.

Results: Low concentrations (10-25 mg·L^{- 1}) of ALA enhanced low temperature-induced oxidative stress tolerance of tomato seedlings. The most effective concentration was 25 mg·L^{- 1}, which markedly increased the ratio of reduced glutathione and ascorbate (GSH and AsA), and enhanced the activities of superoxide dismutase, catalase, ascorbate peroxidase, dehydroascorbate reductase, and glutathione reductase. Furthermore, gene expression of respiratory burst oxidase homolog1 and H₂O₂ content were upregulated with ALA treatment under normal conditions. Treatment with exogenous H₂O₂, GSH, and AsA also induced plant tolerance to oxidative stress at low temperatures, while inhibition of GSH and AsA syntheses significantly decreased H₂O₂-induced oxidative stress tolerance. Meanwhile, scavenging or inhibition of H₂O₂ production weakened, but did not eliminate, GSH- or AsA- induced tomato plant tolerance to oxidative stress at low temperatures.

Conclusions: Appropriate concentrations of ALA alleviated the low temperature-induced oxidative stress in tomato plants via an antioxidant system. The most effective concentration was 25 mg·L^{- 1}. The results showed that H₂O₂ induced by exogenous ALA under normal conditions is crucial and may be the initial step for perception and signaling transmission, which then improves the ratio of GSH and AsA. GSH and AsA may then interact with H₂O₂ signaling, resulting in enhanced antioxidant capacity in tomato plants at low temperatures.

Keywords: 5-Aminolevulinic acid; Chilling; Hydrogen peroxide; Oxidative stress; Redox state; Tomato.

Fig. 1

ALA alleviation of low temperature-induced oxidative stress was dose dependent. Data are expressed as the mean ± standard error of three independent biological replicates. Different letters above the bars indicate a significant difference of P < 0.05

Fig. 2

ALA reduced the RBOH1 transcription and H₂O₂ levels, and improved the Fv/fm at low temperature. a RBOH1 transcription levels (the levels in control plants at 0 h was normalized as 1) and H₂O₂ content; b Images of the Fv/fm, the false color code depicted at the bottom of the image ranges from 0 (black) to 1(red). Data are expressed as the mean ± standard error of three independent biological replicates. Different letters above the bars indicate a significant difference at P < 0.05

Fig. 3

ALA induced upregulation of RBOH1 transcription levels and accumulation of H₂O₂ content under normal conditions. The RBOH1 transcription levels in control plants at 0 h was normalized as 1. Data are expressed as the mean ± standard error of three independent biological replicates

Fig. 4

ALA regulated the redox status of glutathione and ascorbate to inhibit low temperature-induced oxidative stress. a Content of GSH + GSSG, GSH, and GSSG, and the ratio of GSH/GSSG; b Content of AsA + DHA, AsA, and DHA, and the ratio of AsA/DHA. Data are expressed as the mean ± standard error of three independent biological replicates. Different letters above the bars indicate a significant difference at P < 0.05

Fig. 5

Involvement of H₂O₂, GSH, and AsA in ALA-induced oxidative stress tolerance at low temperatures. Data are expressed as the mean ± standard error of three independent biological replicates. Different letters above the bars indicate a significant difference at P < 0.05

Fig. 6

The relationships among H₂O₂, GSH, and AsA in the inhibition of low temperature-induced oxidative stress. Data are expressed as the mean ± standard error of three independent biological replicates. Different letters above the bars indicate a significant difference at P < 0.05