ABSTRACT.
Synthesis and characterization of silica nanoparticles from rice husk and their effects on physiology of rice under salt stress

Preeyanuch Larkunthod1, Jakkree Boonlakhorn2, Payu Pansarakham3, Paweena Pongdontri3, Prasit Thongbai2, and Piyada Theerakulpisut1*
 
Silicon (Si) is considered a beneficial element for rice (Oryza sativa L.) The objective of this work was to investigate the effects of Si in the form of nanoparticles on growth and physiology of rice under salt stress. Silica nanoparticles (SNPs) were synthesized from rice husk by sol-gel method. The prepared SNPs powders were agglomerated in semi-spherical nano-sized particles with diameters in the range of 60-135 nm. Three rice cultivars namely 'Pokkali', 'KDML105' and 'IR29' were grown for 30 d in plastic pots, and then divided into four groups i.e., control, SNPs, NaCl and NaCl + SNPs. Foliar spray of 120 mg L-1 SNPs was given to the SNPs and NaCl + SNPs groups for 4 d. After that the plants in NaCl and NaCl + SNPs groups were exposed to 150 mM NaCl for 17 d. The salt-stressed plants suffered significant reductions in biomass, net photosynthesis rate (PN), and maximal quantum efficiency of photosystem II (PSII) photochemistry (Fv/Fm) while three stress indicators (malondialdehyde, hydrogen peroxide [H2O2] and proline) considerably increased. The SNPs mitigated the adverse effects of salt stress by increasing PN (18% to 116% increase) and lowering H2O2 (8% to 31% reduction) in all cultivars, compared with the values under salt stress, while proline was reduced by 7% in 'KDML105' and 19% in 'IR29'. The H2O2 content was regulated by the increased activities of antioxidant enzymes, notably catalase, peroxidase and ascorbate peroxidase. The application method and concentrations of SNPs used for rice plants under stress should be further optimized for the highest benefit of growth and yield in the field conditions.
Keywords: Antioxidant enzymes, efficiency of PSII, malondialdehyde, net photosynthesis rate, Oryza sativa, proline, rice, salt stress, silica nanoparticles.
1Khon Kaen University, Salt-Tolerant Rice Research Group, Faculty of Science, Department of Biology, Mittraphap Road, Khon Kaen 40002, Thailand.*Corresponding author (piythe@kku.ac.th). 2Khon Kaen University, Faculty of Science, Department of Physics, Mittraphap Road, Khon Kaen 40002, Thailand.3Khon Kaen University, Faculty of Science, Department of Biochemistry, Mittraphap Road, Khon Kaen 40002, Thailand.