The arbuscular mycorrhizal fungus Glomus intraradices induces intracellular calcium changes in soybean cells.

Calcium has been largely hypothesized to be involved in the arbuscular mycorrhizal (AM) signal transduction. A transient elevation in cytosolic Ca2+ concentration is considered one of the earliest responses detected in plant cells challenged with different stimuli. In this paper the detection of Ca2+ transients was selected as a tool to analyse whether plant cells perceive diffusible molecules released by the AM fungus Glomus intraradices. An aequorin-transformed line of soybean cells was used as experimental system. When cells were treated with the medium in which Gl. intraradices spores germinated, a rapid and significant increase in cytosolic Ca2+ level was induced and dissipated within 30 min. The medium did not induce either intracellular accumulation of reactive oxygen species or cell death. A detectable Ca2+ elevation was triggered also by the medium of fungal extraradical mycelium, associated to mycorrhizal hairy roots of carrot. These results indicate that Gl. intraradices releases diffusible molecules that are sensed by host plant cells through a Ca2+-mediated signalling during different steps of its life cycle. Key words: aequorin method, arbuscular mycorrhizal symbiosis, calcium signalling, Glomus intraradices, plant cell cultures.