Characteristics of distribution and chemical forms of Pb in tea plant varieties

A hydroponics experiment combined with subcellular fractionation and sequential extraction was conducted to study the Pb concentration in different organs of two tea plant varieties (Longjing 43 and Yingshuang) and the Pb subcellular distribution and chemical forms in the roots of the varieties. Under Pb stress, the root system of the two varieties had different features in morphology. With the increasing concentration of Pb in culture solution, the Pb concentration in Longjing 43 young leaves increased, but that in Yingshuang' s had no significant variation. A marked difference was observed in the Pb subcellular distribution and its chemical forms in roots between the two varieties under Pb stress. In Longjing 43 roots, all subcellular fractions except soluble ones had a lower Pb concentration at low Pb stress, and all the subcellular fractions except cell wall ones had a higher Pb concentration at higher Pb stress, compared with those in Yingshuang's. In Longjing 43 roots, the HAc-extractable Pb occupied the greatest proportion, followed by NaCl-extractable Pb, HCl- and H2O- extractable Pb, and ethanol-extractable Pb; while in Yingshuang's, NaCl-extractable Pb had the greatest proportion, followed by HAc-extractable Pb, HCl- and H2O-extractable Pb, and ethanol-extractable Pb. Based on these findings, tea plant variety Yingshuang was likely to possess a higher tolerance to Pb than Longjing 43 did.