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 root s 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 withou t inoculum of the arbuscular-mycorrhizal fungus (AMF) Glomus intraradi ces. In control plants (no Cu added) AMF significantly reduced shoot g rowth, but did not affect root growth. At an external Cu supply of 9 m u g (g quartz sand)(-1) or higher, both mycorrhizal colonization and g rowth of roots and shoots of mycorrhizal and nonmycorrhizal plants wer e significantly reduced. With up to 9 mu g Cu g(-1), mycorrhizal colon ization increased the content of cysteine, gamma EC and GSH in the roo ts. However, the amount of thiols in CuBPs was not increased by mycorr hizal colonization in Cu-treated plants and no differences in Cu uptak e 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-inoculate d and inoculated roots of Cu-treated plants. HPLC chromatography of th e CuBPs of both non-inoculated and inoculated roots resulted in a simi lar peak pattern, indicating that no additional CuBPs were formed by t he fungus. In conclusion, our results do not support the idea that AMF protects maize from Cu-toxicity.