Root colonization by arbuscular mycorrhizal fungi is affected by the salicylic acid content of the plant

Wild type, transgenic NahG tobacco plants with reduced levels of salicylic acid (SA) and transgenic CSA (constitutive SA biosynthesis) tobacco plants with enhanced SA levels were inoculated with the arbuscular mycorrhizal fungi (AMF) Glomus mosseae or Glomus intraradices. In a time course study the effect of SA content on root colonization by the fungal symbiont was determined. Throughout the experiment in NahG plants an enhanced root colonization level could be detected, whereas in CSA plants mycorrhization was reduced. At the end of the experiment with Glomus mosseae, root colonization was similar in wild type and in transgenic plants (NahG and CSA plants), indicating that enhanced SA levels in plants can have an effect on delay AMF root colonization, but do not affect the symbiotic potential of plants in terms of changes in maximal threshold of root colonization. Compared to non-mycorrhizal plants, in mycorrhizal wild type and NahG the SA concentration was reduced. The role of SA in the regulation of mycorrhization is discussed. (C) 2003 Elsevier Science B.V. All rights reserved.