Reduced arbuscular mycorrhizal root colonization in Tropaeolum majus and Carica papaya after jasmonic acid application can not be attributed to increased glucosinolate levels

The plant signal compounds jasmonic acid or salicylic acid were applied as abiotic elicitors to leaves of glucosinolate-containing members of the Tropaeolaceae (Tropaeolum majus) and Caricaceae (Carica papaya) and to leaves of the glucosinolate-free plant cucumber. Both compounds are known to induce the accumulation of glucosinolates in Brassica plants. In roots of glucosinolate-containing plants the two compounds enhanced glucosinolate levels or new glucosinolates were accumulated. In all plants treated with jasmonic acid a reduction of root colonization by the arbuscular mycorrhizal fungus Glomus mosseae was observed. No such effect occurred after the salicylic acid treatment. In addition, members of the glucosinolate-containing Tropaeolaceae family were inoculated with the arbuscular mycorrhizal fungus (AMF), and later on the glucosinolate content was determined in roots of mycorrhizal and in roots of non-mycorrhizal plants. Root colonization by the AMF resulted in a large increase of the glucosinolate content, however, the glucosinolate levels in mycorrhizal and in non-mycorrhizal plants showed no effect on root colonization by the AMF. From our results we concluded that the glucosinolate levels can not generally be linked to the non-host status of glucosinolate-containing plants, however, a role of specific glucosinolates in the expression of the non-host status of glucosinolate-containing plants can not be excluded. Moreover, we found that the application of jasmonic acid highly suppresses mycorrhization and this suppression is not a glucosinolate-dependent mechanism.