CuO NP Effects on Lignification in Wheat Seedlings in the Presence of Beneficial Pseudomonad.

Wheat production decreases due to stresses such as drought, high wind, nutrient deficiencies, etc. Preliminary studies demonstrated increased drought tolerance in weed seedlings grown in the presence of CuO NPs and root colonization by Pseudomonas chlororaphis O6 (PcO6). After 5 days of simulated drought conditions the wheat shoots grown with PcO6 and CuO NPs were more rigid than shoots grown without either treatment. The current study investigates whether the rigidity in the shoots was due to lignification as well as higher water content. Surface-sterilized wheat seeds were inoculated with PcO6, and planted into sterile sand amended with 0, 10, and 300 mg Cu/kg from CuO NPs. The wheat seedlings were grown for 7 days. Root and shoot lengths of the harvested plants were measured, tissue was analyzed for moisture, Cu, and lignin contents. Lignin was also analyzed using Toluidine Blue O and phloroglucinol stains, and by FTIR. Results indicated increased lignificationation in vascular bundles and sclerenchyma cells at 10 mg/kg Cu with minimal root shortening relative to the control. The increased lignification may explain the observed increased stiffness of wheat shoots grown in the presence of CuO NPS.