Foliar application of zinc oxide nanoparticles improved yield and 2-acetyl-1-pyrroline content in fragrant rice under salt stress

Abstract

Exogenous application of zinc oxide nanoparticles (ZnO NPs) has been shown to increase the stress resistance of crops, however, its effects on the yield and 2-acetyl-1-pyrroline (2-AP) content of fragrant rice under salt stress remain unclear. The present study investigated the effects of foliar application of ZnO NPs on the yield and 2-AP content of fragrant rice under salt stress. The experiment involved two fragrant rice varieties, i.e. Ruanhuayou1179 and Ruanhuayoujinsi, and four levels of ZnO NPs, i.e. spraying water (CK), 100 ​mg ​L⁻¹ (NP1), 200 ​mg ​L⁻¹ (NP2), and 400 ​mg ​L⁻¹ (NP3), with 0.3​% (5 ​dS ​m⁻¹) saltwater (a mixture of freshwater and seawater). The results demonstrated that the NP1 treatment exhibited the highest yield for both fragrant rice varieties among all treatments, primarily due to an increase in grain number per panicle and grain filling rate. Furthermore, compared with CK, the NP1 treatment significantly enhanced aboveground biomass, chlorophyll content, and potassium ion content in the leaves while reducing malondialdehyde content. Compared with CK, the NP1, NP2, and NP3 treatments significantly increased 2-AP content of both fragrant rice varieties by 46.23-46.67​%, 31.66-43.99​%, and 21.72-39.31​%, respectively, mainly due to increased levels of leaf proline, Δ1-pyrroline-5-carboxylate, 1-pyridine, and methylglyoxal contents. The NP1 treatment also upregulated the 2-AP synthesis enzymes and their gene expression (such as ornithine aminotransferase, diamine oxidase, and Δ1-pyrroline-5-carboxylate synthetase) in comparison with CK. In conclusion, foliar application of 100 ​mg ​L⁻¹ ZnO NPs proved to be the most effective in enhancing both yield and 2-AP content in fragrant rice under salt stress.

Keywords

Antioxidant enzyme activity / Aroma / Fragrant rice / Salt stress / ZnO nanoparticles

Abbreviations

2-AP 2-acetyl-1-pyrroline

BADH2 Betaine betainealdehyde dehydrogenase 2

CAT catalase

DAH days after heading

DAO diamine oxidase

GABA gamma-aminobutyric acid

HS heading stage

HAK17 high-affinity K⁺ transporter protein

MDA malondialdehyde

MS maturity stage

OAT Ornithine transaminase

POD Peroxidase

PDH Proline dehydrogenase

P5C 1-pyrroline-5- carboxylic acid

P5CS Δ1-pyrroline-5-carboxylate synthase

RHY1179 Ruanhuayou1179

RHYJS Ruanhuayoujinsi

SOD superoxide dismutase

SKOR external rectifier K⁺ channel protein

ZnO NPs zinc oxide nanoparticles

Availability of data and materials

The datasets used and/or analyzed during the current study are available from the corresponding author upon reasonable request.

CRediT authorship contribution statement

L.L.: Writing - review & editing, Writing - original draft, Formal analysis, Data curation, Conceptualization. Z.H.: Validation, Methodology, Investigation, Data curation, Conceptualization. Z.Z.: Visualization, Resources, Formal analysis, Data curation. Y.T.: Resources, Project administration, Methodology, Formal analysis. Y.Z.: Supervision, Software, Data curation. Y.M.: Visualization, Software, Resources. S.W.: Project administration, Methodology, Investigation. L.N.: Writing - review & editing, Validation, Investigation, Funding acquisition, Formal analysis.

Declaration of competing interest

The authors declare that they have no any competing interest. Author Lixiao Nie (Editorial Board member) was not involved in the journal's review or decisions related to this manuscript.

Acknowledgments

This work was supported by earmarked fund for HNARS (HINARS-04-G03) and Hainan Major Science and Technology Projects (ZDKJ202001). The authors would also like to express their appreciation to all the students and staff for their contributions to the development of this research.

Appendix A. Supplementary data

Supplementary data to this article can be found online at https://doi.org/10.1016/j.crope.2025.03.004.