NADH or NADPH ?
Using the method of enzymic cycling, the dynamics of pyridine nucleotide concentrations in maize roots and cultured carrot cells after various treatments were studied. The changes were related to transplasmamembrane electron- and proton- transfer rates measured by a pH — redoxstat.
Ethanol increased H+— efflux and, if plants were pretreated with IAA, electron transfer was enhanced too. It has been proposed that this effect is caused by a rise of NADH content due to the action of ADH. In fact, NADH level increased after ethanol treatment. These results would favour NADH as electron donor for the redox system.
In carrot cells, HCF III treatment decreased both NADH and NADPH levels within five minutes. In maize roots, however, the content of NADH was not affected, but a significant decline of NADPH concentration occured after 30 seconds. Similar results could be obtained with the new electron acceptor hexachloroiridate (IV) in maize roots.
In all these experiments, (NADPH + NADP+] and [NADH + NAD+] remained constant. This indicates that the changes in the contents of the reduced forms really reflect their oxidation rather than alterations of the nucleotide synthesis of the plant. Our results also indicate that NAD-kinase which could link the ATP level with the concentrations of the pyridine nucleotides, does not play a significant role in the nucleotide turnover and in the regulation of the redox pump.
Comparing NAD(P)H concentrations with the rates of electron transfer we conclude that there must be a rapid mechanism for back-regulation of the nucleotide content. Otherwise, the whole pool of reduced nucleotides would be completely oxidized within seconds.
KeywordsMaize Root Pyridine Nucleotide Carrot Cell NADPH Level Enzymic Cycling
- HCF III
- HCI IV
Unable to display preview. Download preview PDF.
- Bienfait, 1988: in: Nato ASI Series, this issueGoogle Scholar
- Böttger, M.; Hilgendorf, F., 1988: Hormone influenced e-- and H+- efflux, Plant Physiol. 86, in pressGoogle Scholar
- Craig, T.A.; Crane, F.L., 1981: Evidence for a transplasma membrane electron transport system in plant cells, Proc. Indiana Acad. Sci. 90: 150–155Google Scholar
- Federico, R.; Giartosio, C.E., 1983: A transplasmamembrane electron transport system in maize roots, Plant Physiol. 38: 642–648Google Scholar
- Hampp, R.; Goller, M.; Füligraf, H.; Eberle, I., 1985: Pyridine and adenine nucleotide status and pool sizes of a range of metabolites in choroplasts, mitochondria, and the cytosol/vacuole of Avena mesophyll protoplasts during dark/light transition: effect of pyridoxal phosphate, Plant Cell Physiol. 26 (1): 99–108Google Scholar
- Lüthen H.; Böttger, M., 1988: Hexachloroiridate IV as an electron acceptor for a plasmalemma redox system in maize roots, Plant Physiol. 86, in pressGoogle Scholar
- Monéger, R,; Vermeersch, J.; Lechevallier, D.; Richard, D., 1977: Micro-analyse du NADP et du NAD réduits et oxydés dans les tissus foliaires et dans les plastes isolés de spirodèle et de blé. 1. Problèmes posés par le dosage séparé du extraits végétaux, Physiol. Vég. 15: 29–62Google Scholar
- Peterson, C.A., 1987: The significance of the exodermal casparian band for ion uptake and transport in roots In: X IV. Botanical Congress, Berlin (West), Germany, Ed.: Grenta, W.; Zimmer, B., Benke, H.-D.Google Scholar
- Qiu Z.S.; Rubinstein,B.; Stern, A.I., 1985: Evidence for electron transport across the plasma membrane of Zea mays root cells, Planta 165: 383–391Google Scholar
- Römheld, R.; Marschner, H., 1983: Mechanism of iron uptake by peanut plants. I. FeIII reduction, chelate splitting, and release of phenolics, Plant Physiol. 71: 949–954 16.Google Scholar