Changes in carbon partitioning in pearl millet (Pennisetum glaucum) and clusterbean (Cyamopsis tetragonoloba) in response to ZnO nanoparticle application

Abstract

There is growing interest to study the effect of nano-particles to break productivity barriers of agricultural and horticultural crops. But variations in the response of plants to nano-particles have been reported in the literature. The effects of nanomaterials on the plant growth and development were dependent upon the type of nanoparticles, concentration and plant species besides specific conditions of experiments (Gao et al. 2006, Hong et al. 2005, Ma et al. 2010). Nano-ZnO is being extensively used because of its ultraviolet scattering ability in cosmetics industries besides being used in semiconductors. So chances of its release in environment during industrial processing or dumping are high wherein nano-particles predominantly may get incorporated into sewage sludge and are subsequently applied to agricultural field. Both negative (Lin and Xing 2008) and positive (Adhikari et al. 2010) effects of ZnO nano-particles on roots have been reported. However, studies so far have focused on plant growth but there is no study to our best knowledge that describes the effect on carbon partitioning with emphasis on root exudates. We have therefore studied the effect of nano-ZnO solution as foliar spray on root exudates of important crop plants. Plants were raised in 3 cm diameter glass columns filled with acid washed sand to 40 cm length having G-0 disc at the lower end and fitted with tap at the bottom. Outer surface of the column was covered with black paper followed by aluminum foil to prevent algal growth and to provide dark zone for normal root growth. Columns were vertically arranged on an iron stand as depicted in Fig 1. Columns were initially leached with one-fourth strength of Hoagland solution (Hoagland and Arnon 1950). Two visibly uniform size pearl millet seeds [Pennisetum glaucum (L.) R. Br. emend Stuntz var CZP 9803] surface sterilized with 0.1% mercuric chloride and then soaked in double distilled water for 12 hours were placed at 2 cm depth from surface in the column and covered with moist sand. After seedling emergence, for first seven days, 50 mL Hoagland solution of one-fourth strength was added every day. The leachates were collected in a 100 mL capacity beaker placed at bottom of the column embedded in ice. The tap of the column was kept open. After seven days 50 mL Hoagland solution of complete strength was added and leachates collected every day. Leachates were kept in the deep freeze till analysis. Two weeks after emergence when the plants were at 5-6 leaf stage, 10 mL aqueous solution of 100 mg spherical nano-ZnO/L (prepared and characterized by IIT Mumbai of size range 16-30 nm) was sprayed under pressure in an illuminated enclosure to completely drench. The spray was repeated for 1 Principal Scientist (Plant Physiology) (e mail: uburman@cazri.res.in) Division of Integrated Land Use Farming System, 2 National Fellow 3 Principal Scientist (Nematology) Division of Plant improvement, Propagation and Pest Management, 4 & 5 SRF, NAIP project on Nanotechnology, 6 Principal Scientist (Soil Fertility) Division of Natural Resources and Environment