Innovative auxin-micronutrient based nanocomposites (IAA-Fe2O3NPs and IAA-Mn2O3NPs) shield strawberry plants from lead toxicity.

Abstract

Smart nanohybrid technology with potential advantages to plants has recently been developed formanaging the widespread pollution of heavy metals. Herein, we disclose a novel strategy to combat Pb stress in strawberry (Fragaria spp. cv. Fertona) through a newly designed nano-based system that conjugates indole acetic acid (IAA) with nanoparticles (NPs) of iron (Fe) and manganese (Mn) micronutrients, forming IAA-Mn₂O₃NPs (IAA-MnNPs) and IAA-Fe₂O₃NPs (IAA-FeNPs) nanocomposites and illuminates the underlying mechanisms involved. NPs were synthesized, yielding cubic Mn₂O₃ NPs (50 nm) and spheric Fe₂O₃ NPs (30-40 nm), and evidenced by various characterization techniques. The incorporation of IAA hormone to the surface of NPs was examined using FT-IR spectroscopy. Results showed that Pb harshly hindered strawberry growth and promoted stress oxidative markers, i.e., MDA and ROS byproducts. Notably, the application of IAA-MnNPs and IAA-FeNPs at 50 and 100 ppm moderated the deleterious effects of Pb toxicity in strawberry plants, as revealed by enhanced growth indices, photosynthetic traits, membrane stability, and nutrient profiles of Mn and Fe, as well as higher IAA accumulation. This is pertinent to lessen Pb accumulation and impaired Pb-induced oxidative stress. The decrease in Pb content holds to be filled in with escalating Pb-detoxification mechanisms by enhancing enzymatic antioxidants' activities such as catalase (CAT), superoxide dismutase (SOD), ascorbate peroxidase (APX), glutathione peroxidase (GPX), glutathione S-transferases (GST), phenylalanine ammonia-lyase (PAL), nitrate reductase (NR), and attenuating polyphenol oxidase (PPO). On top of that, IAA-MnNPs and IAA-FeNPs elevated the content of non-enzymatic antioxidants, e.g., ascorbic acid and flavonoids, and enhanced the accumulation of chelating agents, i.e., proline, glutathione, and phytochelatins. We posit that the novel-engineered IAA-MnNPs and IAA-FeNPs nanohybrids present an effective approach that could fend off Pb stress in strawberry plants in contaminated croplands.