ISHS Acta Horticulturae 179: V International Symposium on Growth Regulators in Fruit Production
PROTON TRANSLOCATION SYSTEMS AT THE PLASMALEMMA AND ITS POSSIBLE REGULATION BY AUXIN |
| Author: | M. Böttger |
| Abstract:
Nonelectrolytes like sugars and amino acids are transported uphill into sieve tubes and fruits due to a cotransport of protons, which are flowing downhill due to a proton motive force extending through the outer membrane. This uphill transport thus depends on pH gradient between plasmalemma and apoplast and is influenced by auxin and fusicoccin. The pH-gradient is thought to be maintained by a H + pumping ATPase, because H+ efflux can be reduced by "specific" ATPase inhibitors like vanadate, DCCD and DES. Beside this generally accepted ATPase system, exsists in young expanding tissue a second, hormone directed proton transporting systems. This system is highly sensitive against reduced oxygen level and mainly responsable for the maintainance of the pH gradient of two units between plasma and apoplast. A model of this "non ATPase" redox chain will be described. The energy source is NADH, which is oxidized by a plasmalemma localized enzyme transporting electrons and protons across the membrane. This system has a high Km to oxygen, is stimulated by artificial electron acceptors like ferricyanide and is present in apple fruits. Its possible role in auxin and fusicoccin stimulated sugar uptake will be discussed. | |
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