THIOLS OF CU-TREATED MAIZE PLANTS INOCULATED WITH THE ARBUSCULAR-MYCORRHIZAL FUNGUS GLOMUS INTRARADICES

Mycorrhizal colonization of roots. fresh weight, content of cysteine, gamma-glutamylcysteine (gamma EC), glutathione (GSH), thiol groups in Cu-binding peptides (CuBP), and the uptake of Cu were measured in roots and shoots of maize (Zea mays L., cv. Honeycomb F-1) grown in quartz sand, with Cu at 0, 4.5, 9, 15 and 30 mu g g(-1) added with or without inoculum of the arbuscular-mycorrhizal fungus (AMF) Glomus intraradices. In control plants (no Cu added) AMF significantly reduced shoot growth, but did not affect root growth. At an external Cu supply of 9 mu g (g quartz sand)(-1) or higher, both mycorrhizal colonization and growth of roots and shoots of mycorrhizal and nonmycorrhizal plants were significantly reduced. With up to 9 mu g Cu g(-1), mycorrhizal colonization increased the content of cysteine, gamma EC and GSH in the roots. However, the amount of thiols in CuBPs was not increased by mycorrhizal colonization in Cu-treated plants and no differences in Cu uptake were detected between non-mycorrhizal and mycorrhizal plants. A CuBP-complex with a relative molecular mass of 7 300 and a SH:Cu ratio of 1.77:1 was separated on a Sephadex G-50 column from both non-inoculated and inoculated roots of Cu-treated plants. HPLC chromatography of the CuBPs of both non-inoculated and inoculated roots resulted in a similar peak pattern, indicating that no additional CuBPs were formed by the fungus. In conclusion, our results do not support the idea that AMF protects maize from Cu-toxicity.