Precision nanoparticles for plant thermotolerance: From molecular mechanisms to scalable agriculture.

Heat stress is emerging as a dominant constraint on global crop productivity by destabilizing membranes, disrupting photosynthesis, impairing reproductive development, and accelerating oxidative damage. In recent years, nanoparticles (NPs) have been widely proposed as new regulators of plants thermotolerance, but available literature is rather fragmented, often descriptive and frequently inconsistent across experimental systems. This review provides a critical synthesis of the nanoparticle-mediated heat-stress resistance in most important crops, such as rice, wheat, maize, tomato, and soybean in a mechanistic and systems-level approach. We propose that NPs act as redox modulators, triggering ROS-Ca²⁺-MAPK signaling cascades that activate heat shock transcription factors, stress-responsive gene networks, and hormonal reprogramming, converging downstream on antioxidant reinforcement, membrane stabilization, osmotic adjustment, and photosynthetic protection. Critically, this adaptive response is neither universal nor unconditional; physicochemical parameters including particle size, surface charge, composition, and dissolution kinetics determine whether NP exposure drives hormetic priming or phytotoxic disruption, with this threshold further modulated by crop genotype, developmental stage, and application strategy. Systematic comparison of contradictory findings reveals a mechanistically interpretable pattern: NPs functioning as metabolic co-factors, particularly zinc, selenium, and silicon, consistently confer more stable thermotolerance than non-metabolic exogenous antioxidants such as cerium oxide, which exhibit a narrower efficacy-to-toxicity window. We further identify standardized experimental reporting, genetic verification of HSF-HSP mechanistic claims, multi-location field validation, crop-nutritional-profile-guided NP design, and mandatory pre-commercial ecosystem safety assessment as the critical imperatives required before nanoparticle-enabled thermotolerance can be responsibly deployed at scale.