THE EFFECT OF LEAD ON SEED IMBIBITION AND GERMINATION IN DIFFERENT PLANT-SPECIES

A study was conducted to determine the extent to which seed coats are a barrier to lead and to what degree germination is affected by this h eavy metal. The study was carried out on 25 species of plants from 12 families, represented by different varieties and populations. In all,: 34 types of seeds were tested. Comparative observations were conducted on the effect of barium nitrate on seed imbibition and germination. S eeds were treated with solutions of the following salts during imbibit ion: 100, 1000, and 10 000 mg dm(-3) Pb2+ from Pb(NO3)(2) and 1000 mg dm(-3) Ba2+ from Ba(NO3)(2). The histochemical rhodizonate method was used to determine the distribution of lead and barium in the seeds. Wa ter uptake and germination dynamics were also studied. It was found th at 28% of the studied plant species had seed coats that were permeable to lead ions, 39% were permeable to barium ions. In both cases these species belonged to three families. Papilionaceae, Crucifereae and Gra minae. Lead delayed germination and lowered the ability of seeds to ge rminate in a dose-dependent manner in the species with highly lead-per meable seed coats. In some other species, germination was delayed only a few hours. In all, a significant effect of lead on germination was found in over half of the studied species. It was shown that lead did not act by inhibiting water uptake during imbibition. It was also show n that seed coat permeability varied during imbibition of seeds with c oats highly permeable to lead. Seed coats were impermeable to lead in the first period of imbibition when water uptake is intense. In the fi nal stages of imbibition, when water uptake is reduced. seed coats bec ame more permeable to lead. The lead that penetrated into the embryos in the final stage of imbibition delayed germination. This shows that seed coats are selectively permeable to lead ions. (C) 1998 Elsevier S cience Ireland Ltd. All rights reserved.