Sodium hydrosulfide alleviates aluminum toxicity in Brassica napus through maintaining HS, ROS homeostasis and enhancing aluminum exclusion.

Hydrogen sulfide (HS) is a gaseous mediator that plays versatile roles in plant growth and stress responses. However, the regulatory functions of HS in plant responses to aluminum (Al) stress remain elusive. We observed that application of 20 μM of NaHS (HS donor) or 0.2 mM of hypotaurine (HT, HS scavenger) significantly mitigated the inhibition of rapeseed root growth caused by Al stress (150 μM). Exposure to Al for 6 h induced significant HS accumulation and high levels were maintained thereafter, owing to the elevation of cysteine (83.73 %), L-cysteine desulfhydrase (LCD, 92.32 %), and cyanoalanine synthase (CAS, 11.23 %), and the inhibition of O-Acetyl-l-serine (thiol) lyase (OAS-TL, 15.13 %). Addition of HT significantly scavenged the prolonged HS accumulation caused by Al stress. Exogenous NaHS maintained the HS homeostasis through increasing OAS-TL activity (34.99 %) and inhibiting LCD activity (25.72 %), and cysteine level (39.53 %). Moreover, exogenous NaHS mitigated oxidative damage by enhancing antioxidant enzyme activity (SOD 26.27 %, POD 28.62 %, CAT 400.5 % and APX 92.68 %) and proline content (19.85 %). It also decreased root cell wall Al accumulation (20.52 %) by decreasing PME activity (24.64 %) and facilitating pectin methylation (16.74 %). Similar alleviative effects were observed when HT was added. These results suggest that HS functions differential roles in Al stress response in rapeseed seedlings, depending on its local concentration and duration. Prolonged high HS emissions might contribute to Al toxicity, while moderate exogenous HS improves Al tolerance through controlling HS and ROS accumulation and enhancing Al exclusion through replenishing antioxidant reservoirs and facilitating pectin methylation. It is therefore important that further study investigates how to orchestrate endogenous HS levels and improve plant stress tolerance.