Responses of Pinus massoniana seedlings to lead stress

To investigate the biochemical and physiological responses of Masson pine (Pinus massoniana Lamb.) seedlings to lead stress, needles, stems, and roots of two-year-old seedlings were treated with (PbCO3)-Pb-207 for 33 d and then analyzed 1 and 7 d after the treatment was completed. Chlorophyll (Chl) b responded more sensitively than Chl a to needle Pb treatment, and the Chl content in the needles significantly decreased after Pb application to roots. The malondialdehyde and proline content remained almost unchanged, but superoxide dismutase and catalase activities increased on day 1 after all ways of Pb application. The reduced glutathione (GSH) content and GSH/oxidized glutathione ratio increased on day 1 after Pb application to stem or needles compared to the controls. At 7 d after the Pb application, the increase in dehydroascorbate (DHA) content and the decrease in the ascorbate (AsA)/DHA ratio implied a decreased antioxidant capacity of AsA. The results indicated that the antioxidants were sensitive to the Pb treatments and might be involved in the Masson pine tolerance to Pb stress.