Response of pollen germination and tube growth to cadmium with special reference to low concentration exposure

Cadmium is one of the most important heavy metal pollutants highly hazardou s to plants. Pollen is considered to be more sensitive to pollutants than a re vegetative parts of the plants. Five herb species were tested for respon ses in pollen germination and tube growth to Cd exposure in vitro. Pollen g ermination of all the species was inhibited at Cd concentrations of 2.51 mu g/mL and higher, and tube growth was inhibited at concentrations of 1.58 mu g/ml and higher. Cadmium, at low concentrations, stimulated pollen tube gro wth. The pollen response to Cd stress exhibited interspecies differences. V icia angustifolia and V. tetrasperma were sensitive to Cd, and were inhibit ed in either pollen germination or tube growth by Cd at 0.01 mug/mL. Planta go depressa was less sensitive; pollen germination and tube growth were not inhibited until the Cd concentration reached 2.51 and 1.58 mug/mL, respect ively, and its tube growth displayed two stimulatory peaks; the one that ap peared at 1.00 mug/mL showed the highest tube length in all species tested. These results suggest that Cd, even at low concentrations, may adversely a ffect plant reproduction by inhibiting pollen germination and tube growth. (C) 2001 Academic Press.