Relative Toxicity of Heavy Metals to Red Pine Pollen Germination and Germ Tube Elongation

Abstract

AbstractHeavy metals are known to affect vegetative growth of plants, but little is known concerning the effects of these environmental pollutants on reproductive processes. Hence, the effects of Cd2+, Hg2+, Pb2+, Cu2+, Zn2+, and Ba2+ on red pine (Pinus resinosa Ait.) pollen germination and germ tube elongation were determined in vitro in a series of nine aqueous solutions with concentrations that ranged from 0.56 µmol L−1 to 71.16 µmol L−1 for each cation. Large differences among metals in inhibition of the two growth parameters were found. Based on the lowest concentration significantly inhibiting germination, Cd2+ was the most toxic ion followed by Cu2+ > Hg2+ > Pb2+ ≫ Zn2+ > Ba2+. Similarly, the order for metal inhibition of tube elongation was Cd2+ > Pb2+ > Hg2+ = Cu2+ ≫ Zn2+ > Ba2+. Compared with the other ions, Zn2+ and Ba2+ were relatively nontoxic. The concentration (effective dose) of each metal necessary to produce a 10% reduction of germination and tube elongation (ED10) was calculated from linear regression equations. The ED10 for germination for Cd2+ was 0.27 µmol L−1 and was 2.2, 2.5, and 19.0 times less than the ED10 for Hg2+, Cu2+, and Pb2+, respectively. In comparison, the Cd2+ ED10 for germ tube growth was 1.00 µmol L−1. Although the concentrations of Cd2+, Hg2+, and Pb2+ that produced inhibitory effects in vitro occur in the environment, extrapolation of these results to in vivo conditions is cautioned.