Signal effects of the lectin from the associative nitrogen-fixing bacterium Azospirillum brasilense Sp7 in bacterial-plant root interactions

Azospirillum brasilense, which has the potential to stimulate plant growth, belongs to the group of plant growth-promoting bacteria. The lectin found on the surface of A. brasilense strain Sp7 has the ability to bind specific carbohydrates and ensures adhesion of the bacteria to the root surface. The aim of this work was to investigate possible inductive effects of the Sp7 lectin on the plant cell signal systems. Enzyme-linked immunosorbent assay, spectrophotometry, and thin-layer and gas-liquid chromatography were used to determine the content of signal intermediates in the cells of wheat root seedlings. Laser scanning confocal microscopy was used to examine the localization of fluorescently labeled lectin on the plant cell. The Sp7 lectin acted on the signal system components in wheat seedling roots by regulating the contents of cAMP, nitric oxide, diacylglycerol, and salicylic acid, as well as by modifying the activities of superoxide dismutase and lipoxygenase. The revealed cell membrane localization of the lectin is of deciding importance for its signal function. The results of the study suggest that the A. brasilense Sp7 lectin acts as a signal molecule involved in the interaction of growth-promoting rhizobacteria with plant roots.