Estabishment mechanisms of Azospirillum associaitve nitrogen fixing bacteria on plant roots.

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We investigated mechanisms of how inoculated Azospirillum establishe theirself on plant roots. Following results were obtained.(1)Adhesion capability of bacteria to plant roots was markedly different in bacterial species or plant species used. Bacterial adhesion may be an important process in establishment. However,a direct evidence to support host specificity could not be obtained.(2)Growth characteristics of bacteria absorbed on maize roots showed that increase of bacterial numbers on roots was independent on numbers of adsorbed cells. Growth characteristics was more important factor than bacterial adhesion in estabishment mechanisms.(3)We found bacterial interactions between bacteria coinoculated to maize such as growth stimulation or inhibition. We assume that the interaction is very important mechanisms of the esteblishment ofbacteria on maizee roots.(4)Nitrogen fixation of Azospirillum was not influenced by the mixed inoculation with non-nitrogen fixing bacteria but repressed by combined nitrogen.(5) Carbohydrates in exudate from maize roots was composed of about 85% sugars and 15% organic acids. Glucose was dominantly contained in sugar fraction.(6)Glucose and glyoxylate were function as attractant,although A.brasilense could not assimilate them. Nitrogen source repressed mobility of Azospirillum.(7)Utilization of carbon sources was determined with strains used. It is suggested that the nature of assimilation of carbon surces and competition in uptake of carbon surces among bacteria play an important role in the mechanism of establishment.