Expression of isoenyzmes altered by both Glomus intraradices colonization and formononetin application in corn (Zea mays L.) roots

We searched for and found alterations in isoenzymes that were characteristic of the establishment of the Zea mays-Glomus intraradices symbiosis. Isoenzyme activities for NAD-dependent malate dehydrogenase, esterase, and total peroxidase were examined in corn (Zea mays L. cv. Great Lakes-hybrid 582) roots or mycorrhizas during the first 3 weeks of growth. Soil was either inoculated with the vesicular-arbuscular mycorrhizal (YAM) fungus Glomus intraradices Schenck and Smith or was left uninoculated. Plants were also grown in the presence or absence of formononetin. At 2 weeks of growth, there was an 80% relative increase in colonization in plants that received both formononetin and Glomus as compared to plants inoculated with the mycorrhizal fungus alone. One of the malate dehydrogenase isozyme was differentially expressed in VAM roots at 3 weeks. The activity of this isozyme was further enhanced in the presence of formononetin. At 2 and 3 weeks, four esterase isozymes showed higher activity in mycorrhizas than in non-mycorrhizal roots. Formononetin enhanced the activities of these four esterases following fungal colonization. At 2 weeks of growth. mycorrhizal roots had the highest total peroxidase activity compared to formononetin-treated or control roots. In the presence of formononetin, peroxidase activity was reduced below the amounts of untreated controls. According to these results, the differential expression of certain malate dehydrogenase and esterase isozymes, and the change in total peroxidase activity indicate very early physiological alterations in roots during the establishment of a VAM symbiosis. Furthermore, by examining the shifts in isoenyme activity, the effect of exogenously-applied formononetin on root colonization could be detected at the earliest stages of the Zea-Glomus symbiosis.