The role of wheat germ agglutinin in plant-bacteria interactions: A hypothesis and the evidence in its support

Wheat plants are known to develop the associative symbiosis with the rhizob acterium Azospirillum brasilense. We studied the interaction of a lectin, w heat germ agglutinin (WGA), which is also found in wheat roots, with A. bra silense, strain sp245. When added to the azospirillum culture to the final concentration of 10(-8) to 10(-9) M, WGA enhanced IAA production, dinitroge n fixation, and ammonium excretion by bacterial cells. WGA. also promoted t he synthesis of proteins, both new and those already present in bacterial c ells. The hypothesis that WGA is a signal molecule rerouting the bacterial metabolism in the direction favorable for the growth and development of the host plant has been put forward. It is suggested that signal properties of WGA are the basis for one of the functions of this lectin and essential fo r the effective associative symbiosis.