Stimulation of border cell production in response to increased carbon dioxide levels

Field soil atmospheres have higher CO2 and lower O-2 concentrations compare d with ambient atmosphere, but little is known about the impact of such con ditions on root exudation patterns. We used altered levels of CO2 and O-2 r elative to ambient conditions to examine the influence of the atmosphere on the production of root border cells by pea (Pisum sativum) root tips. Duri ng germination, atmospheres with high CO2 and low O-2, inhibited root devel opment and border cell separation in pea seedlings. Later in development, t he same atmospheric composition stimulated border cell separation without s ignificantly influencing root growth. increased CO2, not low O-2, was respo nsible for the observed stimulation of border cell number. High CO2 apparen tly can override endogenous signals that regulate the number of border cell s released from pea roots into the rhizosphere. The same conditions that st imulated border cell production in pea had no such effect in alfalfa (Medic ago sativa).