A comparative study on the role of conventional, chemical, and nanopriming for better salt tolerance during seed germination of direct seeding rice

Salinity is one of the most significant risks to crop production and food security as it harms plant physiology and biochemistry. The salt stress during the rice emergence stages severely hampers the seed germination and seedling growth of direct-seeded rice. Recently, nanoparticles (NPs) have been reported to be effectively involved in many plant physiological processes, particularly under abiotic stresses. To our knowledge, no comparative studies have been performed to study the efficiency of conventional, chemical, and seed nanopriming for better plant stress tolerance. Therefore, we conducted growth chamber and field experiments with different salinity levels (0, 1.5, and 3‰), two rice varieties (CY1000 and LLY506), and different priming techniques such as hydropriming, chemical priming (ascorbic acid, salicylic acid, and γ-aminobutyric acid), and nanopriming (zinc oxide nanoparticles). Salt stress inhibited rice seed germination, germination index, vigor index, and seedling growth. Also, salt stress increased the over accumulation of reactive oxygen species (H2O2 and O2-·) and malondialdehyde (MDA) contents. Furthermore, salt-stressed seedlings accumulated higher sodium (Na+) ions and significantly lower potassium (K+) ions. Moreover, the findings of our study demonstrated that, among the different priming techniques, seed nanopriming with zinc oxide nanoparticles (NanoZnO) significantly contributed to rice salt tolerance. ZnO nanopriming improved rice seed germination and seedling growth in the pot and field experiments under salt stress. The possible mechanism behind ZnO nanopriming improved rice salt tolerance included higher contents of α-amylase, soluble sugar, and soluble protein and higher activities of antioxidant enzymes to sustain better seed germination and seedling growth. Moreover, another mechanism of ZnO nanopriming induced rice salt tolerance was associated with better maintenance of K+ ions content. Our research concluded that NanoZnO could promote plant salt tolerance and be adopted as a practical nanopriming technique, promoting global crop production in salt-affected agricultural lands.