Astaxanthin synthesized gold nanoparticles enhance salt stress tolerance in rice by enhancing tetrapyrrole biosynthesis and scavenging reactive oxygen species in vitro

Abstract

One of the most common abiotic stresses, high salinity stress, has strictly inhibited plant growth all over the world. Rice is a common food crop, while saline soil has a bad impact on its quality and yield. Nanoparticles (NPs) have been found as an alleviation strategy against abiotic stresses, including salt stress. Astaxanthin is a natural antioxidative oxycarotenoid found in a variety of seafood and microorganisms. We first synthesized astaxanthin gold nanoparticles (Ast-AuNPs) using astaxanthin and chloroauric acid, and then found that 100 mg/L Ast-AuNPs effectively reduced the stress of high salinity (150 mM NaCl) for seven days in hydroponically grown 10-days-old rice seedlings to a greater extent than astaxanthin (100 mg/L) alone. We discovered that supplementing with Ast-AuNPs induced tetrapyrrole biosynthesis while decreasing oxidative stress caused by high salinity. Free proline, malondialdehyde, and hydrogen peroxide levels were dramatically reduced by 45.9%∼51.8%, while antioxidant enzyme activities (peroxidase, catalase, and superoxide dismutase) were expressively increased by 1.85∼3.85 fold with the addition of Ast-AuNPs under salt stress. Furthermore, we found that supplementing rice with Ast-AuNPs induced the expression of ROS-scavenging genes (OsCATA, OsCATB, OsPRX65, OsPRX89, OsCu/ZnSOD1, and OsCu/ZnSOD2) by 2.19∼9.92 fold in leaves. Consequently, these results showed that Ast-AuNPs can benefit rice seedlings coping with high salinity stress by inducing tetrapyrrole biosynthesis, scavenging ROS, and increasing antioxidant activity, and it also expanded the use of functional gold nanoparticles in the treatment of high salinity stress in crops.

Keywords

• Astaxanthin
• AuNPs
• Oryza sativa L.
• Salinity stress
• Tetrapyrrole metabolism