Development of buckwheat root border cells and their impact on Al3+ toxicity after being detached

Root border cells,formerly termed sloughed root cap cells,are defined as cells separated from each other(the apex) and loosely associated with the root so that they disperse into suspension upon immersion of the root tip into water.In the past,border cells have largely been overlooked as a structural and functional component of root systems,but the recently discovered cellular responses of border cells to nematodes,aluminum and fungi suggested novel mechanisms by which border cells might function to protect the root tip from biotic and abiotic stress.To our knowledge,the possible role of root border cells in Altolerance mechanisms has been largely ignored.This study was designed to test the production and development of border cells in buckwheat,and the defense response of border cells in vitro on Al3+ toxicity.The results indicated that most root border cells have a slender claval shape,and few of them have a bend claval shape.Border cells can be observed in roots of 1mm long,and the viability of border cells reached maximum(about 94%) when the root length was 25mm.PME activity increased with emergence of the radicle(1mm) and remained the highest when the root was 5mm in length,at which time PME levels decreased and remained low through 35mm.The increase in exposure time to 50 mol/L Al3+ significantly decreased the survival percentage of border cells in vitro,and dropped to 5% after 48 h treatment.