Hydrogen sulfide (H₂S) is a colorless gas with a characteristic odor of rotten eggs. Although low concentrations of H₂S improve the tolerance of plants to abiotic and biotic stresses, high concentrations are toxic to plant growth. H₂S toxicity-induced primary root (PR) growth inhibition has been reported; however, the signaling pathway underlying H₂S toxicity-mediated root growth and development is still unclear. 

Prof. XU Jin and his team from Xishuangbanna Tropical Botanical Garden (XTBG) of the Chinese Academy of Sciences investigated the effects of exogenous sodium hydrosulfide (NaHS), an H₂S donor, on primary root (PR) growth in Arabidopsis using pharmacological, physiological, and genetic approaches. 

The researchers analyzed the possible involvement of reactive oxygen species (ROS), nitric oxide (NO), and MITOGEN-ACTIVATED PROTEIN KINASE 6 (MPK6) in exogenous H₂S-mediated PR growth. 

They found that H₂S toxicity inhibited PR growth by reducing the meristematic cell division potential. ROS were involved in H₂S toxicity-induced PR growth inhibition. NO was also required for the inhibition of PR growth by exogenous H₂S. 

In addition to the auxin pathway, ROS and NO were also key players in the plant response to H₂S toxicity. ROS production in roots induced by a high concentration of H₂S inhibited PR growth, while ROS accumulation in roots activated MPK6.  

MPK6 then promoted NO production through both L-Arg- and NR-dependent routes. Elevated NO repressed the distribution of auxin in root tips, thereby reducing PR growth.  

The results indicated that H₂S toxicity inhibited PR growth via both the ROS pathway and the auxin signaling pathway. The ROS-MPK6-NO signaling pathway mediated plant responses to H₂S toxicity through morphological and physiological changes in the roots. 

The study entitled “Hydrogen sulfide toxicity inhibits primary root growth through the ROS-NO pathway” has been published in Scientific Reports.