Lead toxicity in germination and growth of Parkinsonia aculeata L. seedlings

Abstract

The high lead (Pb) concentrations in the ground limit the establishment of plants, which makes it necessary to identify tolerant species. The objective of this study was to determine the effect of PbCl₂ and Pb(NO₃)₂ on the germination and early growth of Parkinsonia aculeata seedlings. In the laboratory, the seeds were soaked in solutions of PbCl₂ and Pb(NO₃)₂ at concentrations of 0.0, 0.1, 0.2, 0.5, 1.0 and 2.0 mM. The seeds were weighed at the beginning and at the end (48 h); later, they were incubated and watered with their respective solutions (7 days). In the greenhouse, the seeds were sown in sand and watered (15 days) to determine the germination percentage (laboratory) and emergence (greenhouse): stem length, radicle and dry weight (both conditions). In the laboratory, PbCl₂ and Pb(NO₃)₂ did not affect imbibition, but by increasing their concentrations, they significantly reduced germination by 18 and 26 %, respectively, as well as the dry weight of the stem (40 and 49 %), and radicle (40 and 57 %). In the greenhouse, the Pb compounds reduce emergence little, and did inhibit radicle growth; while Pb(NO₃)₂ inhibited in greater proportion the dry weight. The effect of Pb may differ depending on the Pb compound used, with Pb(NO₃)₂ presenting greater toxicity.