Response of lettuce to silver nanoparticles under drought conditions

Nano-fertilization is an emerging technology to improve agricultural productivity under diverse ecosystems. Our study was conducted to investigate the effects of foliar fertilization of silver nanoparticles (AgNPs) on the growth, enzyme activities and water use efficiency (WUE) of lettuce (Lactuca sativa, L.) under drought conditions. A pot culture study with 4 AgNPs rates x 2 stress levels in a factorial combination of randomized complete block (RCB) design was conducted. The AgNPs levels were 0 (control), 25, 50, 75 and 100 mg/L) were imposed on lettuce seedlings under ambient and simulated drought (similar to 50% field moisture capacity of soil) conditions. Lettuce plant height, total yields, leaf relative water content (RWC), chlorophyll content, membrane injury (MII), glutathione S-transferase (GST), glutathione reductase (GR), carboxylesterase (CaE), total phenolics and flavonoids and WUE were determined and/or calculated. The results showed that GST activity reduced in treatments of AgNPs + stress compared to stressed plants. In treatment of 100 mg L-1 AgNPs + stress, GR activity increased in treatments of 25, 50 and 75 mg L-1 AgNPs, but showed a significant decrease in 100 mg L-1 AgNPs + stress. CaE activity enhanced in 100 mg L(-1 )AgNPs + stress (about 1.55-fold) compared to stressed plants. Total flavonoid and phenolic contents were the highest in 50 mg L-1 AgNPs + stress. It was not obtained significant effects in the WUE rates. In 100 mg L-1 AgNPs, MII rates were the highest, and RWC rates were the lowest. Leaf width, plant height and total yield decreased at doses of AgNPs