Hydrogen Sulfide Interacts with 5-Aminolevulinic Acid to Enhance the Antioxidant Capacity of Pepper (Capsicum annuum L.) Seedlings under Chilling Stress

Huiping Wang,Jianming Xie,Jing Zhang,Zeci Liu,Jing Li,Shilei Luo

doi:10.3390/agronomy12030572

Abstract

5-Aminolevulinic acid (ALA) is the precursor of tetrapyrrole synthesis, and hydrogen sulfide (H2S) is a gas signal molecule. Studies have shown that exogenous ALA and H2S can alleviate abiotic stress. This study evaluated the roles of ALA and H2S and their interactions in regulating antioxidant activity in pepper seedlings under chilling stress. Chilling stress significantly inhibited the growth of pepper seedlings and increased the amounts of hydrogen peroxide (H2O2), superoxide anion (O2•−), and malondialdehyde (MDA). ALA and/or H2S increased the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT). Moreover, ALA and/or H2S enhanced the ascorbate (AsA)-glutathione (GSH) cycle by increasing the contents of AsA and GSH, the ratio of AsA to dehydroascorbic acid and GSH to glutathione disulfide increased, and the activities of ascorbate peroxidase (APX), glutathione reductase (GR), dehydroascorbate reductase (DHAR) and monodehydroascorbate reductase (MDHAR) also increased. At the transcriptional level, ALA and/or H2S upregulated the expressions of CaSOD, CaPOD, CaCAT, CaAPX, CaGR, CaDHAR, and CaMDHAR in seedlings under chilling stress. ALA and/or H2S also reduced the contents of H2O2, O2•− and MDA, eventually mitigating the inhibitory effects of chilling stress on pepper seedling growth. The combination of ALA and H2S had a better effect than ALA or H2S alone. Moreover, ALA and H2S interact to regulate the oxidative stress response of pepper seedlings under chilling stress.

Highlights

The plant height, stem thickness, blade quantity, shoot fresh weight, and root fresh weight were significantly reduced in the group treated with Aminolevulinic acid (ALA) + HT compared to the ALA (Figure 1B–F). These results indicate that the application of exogenous ALA and/or hydrogen sulfide (H2 S) significantly alleviated the growth-inhibiting effects of chilling stress in pepper seedlings
No significant difference in GSH/GSSG ratio was observed between the ALA + HT and CK groups (Figure 4C). These results suggest that ALA increased the GSH/GSSG ratio in pepper seedlings subjected to chilling stress for 24 h by increasing the GSH content and decreasing the GSSG content; H2 S increased the GSH/GSSG ratio primarily by decreasing the GSSG content
There were no significant differences in the dehydroascorbate reductase (DHAR) and monodehydroascorbate reductase (MDHAR) activities, or the relative expression levels of CaDHAR and CaMDHAR between the ALA + HT and CK groups (Figure 7A–D). These results suggest that ALA and H2 S enhanced the relative expressions of CaAPX, CaGR, CaDHAR, and CaMDHAR in pepper seedlings under chilling stress, with the combination of ALA and NaHS having the most significant effect

Summary

Introduction

In winter and spring, chilling is the main abiotic stress that limits the growth, development and yield of pepper [1]. Plants produce a large amount of reactive oxygen species (ROS), including singlet oxygen (1 O2 ), hydrogen peroxide (H2 O2 ), hydroxyl radical (HO ), and superoxide anion (O2 − ) under chilling stress, which cause cell oxidative damage when produced in excess [5,6,7]. ROS led to irreversible DNA damage and cell death; on the other, ROS regulate plant growth and stress as signaling molecules [8,9]. Plants have a complex and complete antioxidant system to remove ROS and protect cells from oxidative damage [6,10]. The antioxidant systems in living organisms mainly depend on antioxidant molecules, antioxidant enzymes, and some osmotic regulatory substances [11,12]

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Conclusion