INFLUENCE OF TEMPERATURE ON PROTON SECRETION AND HEXACYANOFERRATE(III) REDUCTION OF ZEA-MAYS L ROOTS

Responses of potassium hexacyanoferrate (III) [HCF(III)] reduction and net proton secretion by Zea mays L. cv Goldprinz roots to changes in ambient temperature were investigated. Arrhenius plots of proton secretion and redox activity showed a constant slope between 5 and 20-degrees-C, indicating that reaction kinetics do not change. Proton secretion without HCF(III) was strongly temperature dependent. This dependence was not altered when H+ efflux was stimulated by fusicoccin or by increased K+ concentration. The temperature coefficient for HCF(III) reduction was low, indicating that the velocity of this reaction was limited by apoplastic diffusion of the ferric complex. In the presence of HCF(III) but not hexacyanoferrate (II), temperature dependence of proton efflux markedly declined, indicating fundamental changes in the process(es) contributing to net proton secretion. It is concluded that HCF(III) establishes a proton extrusion path that is directly linked with the reduction reaction.