Lead-induced changes in germination behavior, growth and inhibition of -aminolevulinic acid dehydratase activity in Raphanus sativus L.

The seed germination test under lead (Pb) stress could be a quick test to understand plant tolerance to this heavy metal. The aim of this study was to compare the germination behavior of Raphanus sativus L. germinated in solution with different increasing concentration of lead, also to assess its accumulation and toxicity. The test was carried out in an incubator at 25 ± 1°C for 7 days and in a greenhouse for 11 weeks. Lead caused significant germination behavioral disturbances by changing the velocity coefficient and germination kinetics, with reducing the rate of early and final germination, however, the duration of germination was lengthened. Pb reduced the levels of the chlorophyll, delta-aminolevulinic acid dehydratase (ALAD) activity and growth. It increased lipid peroxidation and induced a significant accumulation of proline, positively correlated with Pb accumulation. Pb has a depressive effect on germination and causes disruptive disturbances of R..  sativus L. revealed by changes in non-enzymatic antioxidants, ALAD activity and growth. Radish has a capacity to accumulate Pb. The present results provide a model for detecting natural compounds able to improve seed germination of radish and counteract the harmful effects of lead.   Key words: Radish, concentration, rate, accumulation, proline, lipid peroxidation, chlorophyll.