Zinc oxide nanoparticles (ZnO NPs) stabilized by phytocellulose derived biopolymer and their bipartite interaction studies with agriculturally important microbes/Raphanus sativus (L.) seeds

Abstract

Zinc oxide nanoparticles (ZnO NPs) are one of the most studied metal oxide NPs (MONPs) owing to their unique physiochemical properties. The last few years have witnessed a growing interest among researchers in adopting the green chemistry approach to fabricate MONPs. We herein report the synthesis of ZnO NPs stabilized by carboxymethyl cellulose (CMC) derived from noxious aquatic weed, i.e., Eichhornia crassipes biomass (EC-CMC). The UV–Vis spectra showed maximum absorbance at ∼380 nm, and the XRD crystallite size of EC-CMC capped ZnO NPs (c-ZnO NPs) (∼26 nm) was smaller as compared to virgin ZnO NPs (v-ZnO NPs) (∼29 nm). The value of apparent strain (εA x 10−3), root mean square strain (ERMS x 10−3), stress (MPa), and energy density (KJm−3) for c-ZnO NPs obtained from the SSP plot was ∼0.893, ∼0.173, ∼116 and ∼51.83 respectively. The study also examined the differential effects of c-ZnO NPs treatment on the growth of two plant growth-promoting rhizobacteria (PGPR), i.e., Pseudomonas fluorescens (Gram -ve), and Bacillus subtilis (Gram +ve). The findings revealed that P. fluorescens (PFL) was more susceptible to c-ZnO NPs than B. subtilis (BST). Furthermore, R. sativus seeds treated with c-ZnO NPs (10–50 ppm) exhibited notable improvements in plumule length, radicle length, vigor index, and biomass content over other treatments and control. The biopriming of R. sativus seeds with PFL and BST showed synergistic effects with 10-ppm c-ZnO NPs treatment and promoted overall seedling growth. The bacterial kinetics and seed germination studies manifest that the c-ZnO NPs at lower doses have growth-promoting effects. The combination of PFL + BST+10-ppm c-ZnO NPs showed substantial improvements in the germination indices of R. sativus. The present work has demonstrated the potential of utilizing positive bipartite interaction of PGPRs and bio-stabilized ZnO NPs to develop nanoformulations promoting plant growth management.