Stimulation of the ionic transport system in Brassica napus by a plant growth-promoting rhizobacterium (Achromobacter sp.)

A plant growth-promoting rhizobacterium belonging to the genus Achromobacte r was isolated from the oilseed-rape (Brassica napus) root. Growth promotio n bioassays were performed with oilseed rape seedlings in a growth chamber in test tubes containing attapulgite and mineral nutrient solution, contain ing NO3- as N source. The presence of this Achromobacter strain increased s hoot and root dry weight by 22-33% and 6-21%, respectively. Inoculation of young seedlings with the Achromobacter bacteria induced a 100% improvement in NO3- uptake by the whole root system. Observations on the seminal root o f seedlings 20 h after inoculation showed that there was an enhancement of both the number and the length of root hairs, compared to non-inoculated se edlings. Electrophysiological measurements of NO3- net flux with ion-select ive microelectrodes showed that inoculation resulted in a specific increase of net nitrate flux in a root zone morphologically similar in inoculated a nd non-inoculated plants. The root area increased due to root hair stimulat ion by the Achromobacter bacteria, which might have contributed to the impr ovement of NO3- uptake by the whole root system, together with the enhancem ent of specific NO3- uptake rate. Moreover, inoculated plants showed increa sed potassium net influx and proton net efflux. Overall, the data presented suggest that the inoculation of oilseed-rape with the bacteria Achromobact er affects the mineral uptake.