Affiliations: College of Science, Nanjing Agricultural University,
Nanjing 210095, China. E-mail: [email protected] | Department of Biology, Hong Kong Baptist University,
China
Abstract: Agrogyron elongatum were grown in nutrient solution containing
moderate to high amounts of separate heavy metal of Cd, Cu, Ni and Pb in a
greenhouse for a 9-day. Cd, Cu, Ni and Pb generally led to decrease in the
elongation of roots although the length of seedlings exposed to Cd and Pb at
0,05 and 0.5 mg/L showed to be slightly greater than that of controls. Of the
four metals in the experiment, Pb was absorbed and accumulated to the highest
level, with the concentrations of 92754 mg/kg dry weight (DW) in roots and
11683 mg/kg DW in shoots. Cd was moderately accumulated in Agrogyron elongatum,
but the maximum bioaccumulation coefficients (BCs) for rpots and shoots were
observed. The patterns for Cu and Ni uptake and distribution in plants differed
from those of Pb and Cd, as it was showed that the shoot accumulation of Cu and
Ni was significantly higher than in roots. A. elongatum had the highest Ni
concentration in shoots (30261 mg/kg DW)at the external concentration of 250
mg/L. Cu ranked second, with a shoot concentration of 12230 mg/kg DW when 50
mg/L Cu in solution was applied. For the four trace elements tested, the
highest concentrations in shoots decreased by the order of Ni > Cu > Pb
> Cd (mg/kg DW),and those in roots were Pb > Cd > Ni > Cu (mg/kg
DW). Malic, oxalic and citric acids exuded by roots exposed to 1 and 50 mg/L of
the metals were detected. Release of organic acids from plants significantly
differed among the metal treatments. Cu was most effectively in inducing rpot
exudation of the three types of organic acids. Cd, and Ni were also the
inducers of secretion of malic and oxalic acids. With reference of Pb,a small
amounts of malic and oxalic acids were detected in the root exudates, but few
quantities of citric acid were found. However, no orrelation between
alternations in root exudation of organic acids and metal accumulation could be
established.
Keywords: heavy metal, organic acid, Agrogyron elongatum, hyperaecumulation
