Spermidine carbon dots enhance thermotolerance by modulating photosynthesis and cellular redox homeostasis in tomato

Abstract

In this study, we demonstrate and elucidate how spermidine carbon dots (Spd-CDs) enhance tomato tolerance under heat stress (45 °C). Foliar-applied Spd-CDs (6 mg L⁻¹) have a higher maximum quantum efficiency of PSII (45.3%) and net photosynthesis rate (38.6%) compared to after heat stress for 12 hours. Similarly, 6 mg L⁻¹ Spd-CDs increased the maximum ribulose-1,5-bisphosphate regeneration rate, maximum ribulose-1,5-bisphosphate carbohydrate/oxygenase carboxylation rate by 10.6% and 41.7%, 33.9% and 82.4%, respectively, accompanied by obvious physiological responses of chloroplast and increased the electron transfer rate (21.3% and 23.1%) were found under normal (25 °C) and high temperature, respectively. Heat stress-induced oxidative stress was significantly alleviated in Spd-CD-treated plants through the lowered accumulation of reactive oxygen species (ROS) (20.7%) and lipid peroxidation (10.9%), along with an elevated ratio of glutathione/oxidized glutathione (GSH/GSSG) (22.6%) and ascorbate acid/dehydroascorbic acid (AsA/DHA) (78.8%), and other antioxidant enzymes, including the ascorbate peroxidase (52.3%), monodehydroascorbate reductase (20.1%), dehydroascorbate reductase (18.3%), glutathione reductase (14.3%), glutathione S-transferase (16.2%), catalase (32.0%), superoxide dismutase (22.9%). Furthermore, using an inhibitor of GSH biosynthesis, buthionine sulfoximine, the Spd-CD induced heat tolerance was compromised, indicating that Spd-CDs induced thermotolerance may be dependent on the AsA–GSH cycle. Taken together, the application of Spd-CDs safeguarded the photosystem complex and ameliorated oxidative damage, thus enhancing thermotolerance. This study put forward that Spd-CDs are a potential tool for plants that are better addressed to the challenges of climate change.