Heterotic behaviour of the transmembrane electric potential difference in some maize hybrid-parents combination

In three hybrid-parents combinations the transmembrane (vacuole-exterior) electric potential difference (PD) of cortical cells of maize root is significantly (approx. 15%) higher in the hybrids than in their parental inbreds. To investigate the nature of this PD difference the PD of cortical cells of subapical maize root segments from the inbreds Mo17 and B73 and their hybrid was measured under the following conditions: (1) inhibition of glycolytic and mitochondrial ATP synthesis by AsO43-; (2) inhibition of mitochondrial ATP synthesis and permeabilization of the plasmalemma to H+ by carbonylcyanid-p-trifluorometoxyphenylhydrazon (FCCP); (3) activation of active electrogenic H+ extrusion by fusicoccin. The results show that: (I) The inhibition of the active PD component by either AsO43- or FCCP lowers the PD-values more in the hybrid than in the inbreds, so that after 30-60 min of treatment no difference is observed any more between the three lines. This suggests that the higher PD of the hybrid depends on a higher rate of operation of the active electrogenic mechanism. (II) The treatment with fusicoccin (FC) increases the PD-values of the three maize lines, but more so in the inbreds than in their hybrid. This may suggest that the potentiality of the electrogenic H+ extrusion mechanism is more efficiently expressed in the hybrid.