The Seed Germination Test as a Valuable Tool for the Short-Term Phytotoxicity Screening of Water-Soluble Polyamidoamines

Six differently charged amphoteric polyamidoamines, synthesized by the polyaddition of <i>N</i>,<i>N</i>'-methylenebisacrylamide to alanine, leucine, serine, arginine (M-ARG), glutamic acid (M-GLU) and a glycine/cystine mixture, were screened for their short-term phytotoxicity using a seed germination test. <i>Lepidium sativum</i> L. seeds were incubated in polyamidoamine water solutions with concentrations ranging from 0.156 to 2.5 mg mL^-1 at 25 ± 1 °C for 120 h. The seed germination percentage (<i>SG</i>%), an indicator of acute toxicity, and both root and shoot elongation, related to plant maturation, were the considered endpoints. The germination index (<i>GI</i>) was calculated as the product of relative seed germination times relative radical growth. The <i>SG</i>% values were in all cases comparable to those obtained in water, indicating no detectable acute phytotoxicity of the polyamidoamines. In the short term, the predominantly positively charged M-ARG proved to be phytotoxic at all concentrations (<i>GI</i> < 0.8), whereas the predominantly negatively charged M-GLU proved to be biostimulating at intermediate concentrations (<i>GI</i> > 1) and slightly inhibitory at 2.5 mg mL^-1 (0.8 < <i>GI</i> < 1). Overall, polyamidoamine phytotoxicity could be correlated to charge distribution, demonstrating the potential of the test for predicting and interpreting the eco-toxicological behavior of water-soluble polyelectrolytes.