Fluorescent Properties and Bifenthrin Binding Behavior of Maize (Zea mays L.)

Bifenthrin is one of the widely used pyrethroid pesticides in agriculture, public health, homes and gardens. It is the most persistent synthetic pyrethroid in soil with its half-life ranging from 122 to 345 days. Bifenthrin is frequently detected in the soil and sediment. Now, bifenthrin pollution of soil is a growing environmental concern.

Plant root can persistently exude large amount of organic substances, which are composed of amino acids, carbohydrates, mucilage and low molecular weight secondary metabolites. Root exudates can bind metals in soil and enhance the availability of heavy metals and organic pollutants to plant. The binding parameters of root exudates for organic pollutants are important for understanding the mechanisms involved in phytoavailability and phytoremediation. However, quantitative information about organic pollutant binding to root exudates is lacking.

The fluorescence excitation emission matrix (EEM) spectrometry is a rapid and sensitive technique that can quantitatively characterize the interaction of fluorescent organic matter and pollutants. Because proteins show fluorescent properties and are also key components of root exudates, EEM fluorescence spectroscopy should be a powerful technology for studying the fluorescent components in root exudates and their interactions with pollutants.

In order to quantify the binding behavior of plant root exudates for bifenthrin under various pH conditions using EEM fluorescence spectroscopy, Prof. PAN Xiangliang and other researchers investigated fluorescent properties and bifenthrin (insecticide) binding behavior of root exudates from maize (Zea mays L.) seedlings. The result showed that the protein-like fluorophores in root exudates from Z. mays L. are strong complexing ligands for bifenthrin, with logK_a in the range of 3.6-5.7. Two protein-like fluorescence peaks were identified in the EEM spectrum of root exudates and fluorescence of both peaks could be quenched by bifenthrin. The protein-like substances in root exudates had larger binding capacity for bifenthrin under acidic condition than under neutral and basic condition. The conditional stability constants were also higher in acidic solution than in the neutral or basic solution. Similarly, more fluorescence is accessible for bifenthrin at acidic pH. More than one binding sites are needed in root exudates for binding one bifenthrin molecule. The result indicated that more attention should be paid to the effects of root exudates on adsorption, transport and fate of pesticides in environments.

The result has been published on European Journal of Soil Biology, 2012, 50: 106-108. The paper is also archived at http://www.sciencedirect.com/science/article/pii/S1164556312000027.