EFFECT OF SILVER NANOPARTICLE (AgNPs) ON 'KDML 105' RICE Oryza sativa L. SEEDLINGS

Abstract

This research was aimed to study the effects of different sizes 20, 30-70, 70-120 and 150 nm and different concentration 0.1, 1, 10, 100 and 1,000 mg/L of AgNPs on rice Oryza sativa L. seedlings under normal and salt stress conditions based on the hypothesis that AgNPs had affected on rice seedlings growth by possibly inhibition or induction of rice growth, including morphological and physiological changes.The results revealed that under normal and salt stress conditions, all growth parameters, including fresh weight, dry weight, shoot height and root length were decreased relatively to the increasing size and concentration of AgNPs pretreatment by 24 hour-seed soaking prior to germination. The positive result was detected under salt stress condition, when the seeds were soaked with 1 or 10 mg/L of 20 nm AgNPs. The AgNP pretreatment significantly enhanced root fresh weight and root length in comparison with the control and other treatments. Based on the analysis of AgNPs accumulation in plant tissue, the higher uptake was found when the rice seeds were treated with smaller size of AgNPs. However, the high level of 20 nm AgNP uptake was trapped in the root rather than transported to the leaves. Therefore, the smaller size had the less negative effect on seedlings growth than the larger one, 150 nm diameter AgNPs. Cell disruption in the seedling leaves was detected, when the seeds were pretreated with 150 nm AgNPs at the higher concentration (100 mg/L). Moreover, hydrogen peroxide (H2O2) content and anti-oxidative enzyme activities were quantified under normal and salt stress conditions. When seeds pretreated with AgNPs, H2O2 was induced in both normal and salt stress conditions. The level of H2O2 contents in the salt treated plants was higher. The seed pretreatment with the 150 nm AgNPs at concentratin of 100 mg/L significantly increased hydrogen peroxide higher than control, suggesting the higher level of stress was induced by AgNP pretreatment. These supported the growth inhibition effects by AgNPs. Furthermore, 100 mg/L of 150 nm AgNP presoaking enhanced CAT, SOD, APX, GR and GPX activity. The interesting results were detected under salt stress condition when seeds were exposed to 10 mg/L of 20 nm AgNPs. SOD and APX activity in roots of seedlings germinated from the pretreated seeds were higher than the activities detected in no AgNP pretreatment control. This suggested that the appropriate size and concentration of AgNPs can be used as seed- priming agent for salt stress acclimation.