Substrate-dependent modulation of ATPase activity by Na('+) and K('+) in roots of Plantago species [Ion uptake, Plantago maritima, Plantago coronopus]
1980
Erdei, L. | Kuiper, P.J.C. (Rijksuniversiteit Groningen (Netherlands). Dept of Plant Physiology, Biological Centre)
The separate and combined effects of Na('+) and K('+) on ATPase activity of microsomal fractions from the roots of the halophytic Plantago maritima and the less salt-tolerant Plantago cornopus were investigated in the presence of Mg + ATP or Ca + ATP (at equimolar ratios) as substrate. The ATPase activity in the presence of Mg + ATP was stimulated by Na('+) and by K('+) when they were added separately, but their combination reduced the enzyme activity. In the presence of Ca + ATP, however, the enzyme activity was stimulated by the combined addition of Na('+) + K('+) as well, and their action was qualitatively additive, but experimentally lower. The two complexes as substrate probably served as allosteric effectors and induced different types of enzyme responses to monovalent cations. The Na('+)-stimulation and K('+)-stimulation of the ATPase activity could be separated by growing the plants under saline conditions. The Na('+)-stimulation of the ATPase was lowered while the K('+)-stimulation remained unchanged. The corresponding Na('+) influx of the roots could also be blocked without influencing K('+) influx of the roots. This kind of separation of ion fluxes and ATPases presumes a transport system model which possesses several units and which is accessible for regulation by hormones, lipids and divalent cations
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