Changes in net proton release by roots of intact maize plants after local nutrient supply in a split root system

The effect of local nutrient supply to maize roots (Zen mays L. cv. Blizzar d) on net proton release was studied using the split root technique (SRNS, SRCa) to compare plants that were cultivated with their roots completely in either nutrient solution (NS) or 0.1 mM CaSO4 (Ca). Roots in NS released m ore protons than roots in Ca. This higher net proton release was associated with significantly higher ATP concentrations in the root tissue. Higher ne t proton release and ATP concentrations were also observed after a 4 h lag phase when 20 mu M abscisic acid were exogenously applied to roots in 0.1 m M CaSO4. It is suggested that higher metabolic activity in roots supplied w ith nutrients increased ATP concentrations and thus the substrate supply of the plasma membrane H+ ATPase. When only half of the root system was suppl ied with nutrient solution with the other half bathed in 0.1 mM CaSO4, the roots in the SRNS compartment released significantly higher amounts of prot ons relative to the NS control plants. Conversely, roots in the SRCa compar tment showed net proton uptake in contrast to the roots of control plants i n 0.1 mM CaSO4 which significantly acidified the root medium. These differe nces in proton release by roots in the split root system and control roots could not be explained in terms of differences in ATP concentrations. It is therefore suggested that an internal signal may lead to a modification of the plasma membrane H+ ATPase as :shown earlier during plant adaptation to low pH in the root medium.