Preparation of a thermoresponsive maize seed coating agent using polymer hydrogel for chilling resistance and anti-counterfeiting

Sweet-waxy corn is susceptible to chilling injury, and vulnerable to be counterfeited. This study developed a kind of newly thermoresponsive coating material with dual efficacies of intelligent chilling-resistant and anti-counterfeiting for maize seed. The coating material was named as PRBSA, which was made of salicylic acid (SA) and rhodamine B (RB) co-loaded poly (N-isopropylacrylamide-co-butylmethacrylate) hydrogel. The surface morphology of PRBSA was compact than its interior, where it was uneven and irregularly distributed pore structure. Below the lower critical solution temperature (LCST), PRBSA was water-soluble and hydrophilic, loaded SA and RB could release sharply from PRBSA, whereas above this LCST, PRBSA formed an insoluble and hydrophobic aggregate, the release rate of SA and RB was obviously decreased. Meanwhile, PRBSA showed a better thermal stability than unloaded hydrogel. In addition, seeds were coated with PRBSA, and its seedling quality and fluorescence labeling under chilling stress were determined. These results showed that compared with the CK (basic coating agent), PRBSA treatment significantly enhanced seed germination percentage by 17.8% and vigor index by 53.1% under chilling stress. The seedling shoot height and dry weight were also significantly improved, which might closely related with the lowest malondialdehyde and relative electrical conductivity level, and the highest maximal quantum yield of PSII (Fv/Fm). Moreover, the surface of PRBSA coated seeds showed bright red fluorescence under the excitation green light of 546 nm. When responding to low temperatures, its fluorescence intensity exhibited a sharp decline, showing a temperature-sensitive release of RB. Therefore, PRBSA was considered as a novel seed coating with intelligent chilling-resistant and anti-counterfeiting function.