5-Aminolevulinic acid and hydrogen sulphide alleviate chilling stress in pepper (Capsicum annuum L.) seedlings by enhancing chlorophyll synthesis pathway

Abstract

5- Aminolevulinic acid (ALA) as a precursor in chlorophyll (Chl) synthesis and hydrogen sulphide (H₂S) as a gas signalling molecules can alleviate various abiotic stresses by enhancing photosynthesis. However, little is known about their mechanisms ameliorating photosynthesis under chilling stress, or interactions of ALA and H₂S in Chl synthesis. In this study, we explored the effects of exogenous ALA and H₂S on chilling stress-induced photosynthesis damage in pepper (Capsicum annuum L.) seedlings. Chilling inhibited the photosynthetic capacity of pepper seedlings, ALA or H₂S treatment alone could alleviate this inhibition, and ALA + H₂S treatment was even more effective for improving photosynthetic capacity. Additionally, levels of Chl synthesis pathway substances including endogenous ALA, protoporphyrin IX (Proto IX), Mg-protoporphyrin (Mg-Proto IX), protochlorophyllide (Pchl) and Chl (Chl a and Chl b) were significantly decreased, and chilling down-regulated upstream genes HEMA1, HEMB, FAR1, FHY3, CHLH, HEME1, HEMF and PORA. ALA + H₂S treatment significantly increased levels of Chl and upstream substances, and up-regulated expression of HEMA1, HEMB and FAR1. In conclusion, exogenous ALA and H₂S enhanced chlorophyll synthesis pathway, and thus improved the photosynthesis of pepper seedlings under chilling stress.

Keywords: ALA; Chilling stress; Chlorophyll; H(2)S; Pepper; Photosynthesis; Transcriptional regulation.