Transport of Mg²⁺ and Ca²⁺, and Mg²⁺‐stimulated adenosine triphosphatase activity in oat roots as affected by mineral nutrition

Abstract

Mg2+‐ and Ca2+‐uptake was measured in dark‐grown oat seedlings (Avena sativa L. cv. Brighton) cultivated at two levels of mineral nutrition. In addition the stimulation of the ATPase activity of the microsomal fraction of the roots by Mg2+ was measured. Ca2+‐uptake by the roots was mainly passive. Mg2+‐uptake mainly active; the passive component of Mg2+‐uptake was accompanied by Ca2+‐efflux up to 60% of the Ca2+ present in the roots. In general Mg2+ ‐uptake of oat roots was biphasic. The affinity of the second phase correspond well with that of the Mg2+‐stimulation of the ATPase activity, in low‐salt roots as well as in high‐salt roots and in roots of plants switched to the other nutritional condition. Linear relationships were observed when [phase 2] Mg2+‐uptake was plotted against Mg2+‐stimulation of the ATPase activity of the microsomal fraction of the roots. In 5 days old high‐salt plants 1 ATP (hydrolysed in the presence of Mg2+ J corresponded with active uptake of a single Mg2+ ion, but in older high‐salt roots and in low‐salt roots more ATP was hydrolysed per net uptake of a Mg2+ ion. The results are discussed against the background of regulation of the Mg2+‐level of the cytoplasm of root cells by transport of Mg2+ by a Mg2+‐ATPase to the vacuole, to the xylem vessels, and possibly outwards.

A mechanism for multiphasic uptake of solutes in plants

“…Several lines of evidence indicate that ATPases are implicated in active ion uptake (Hodges 1976, Stok et al 1981. In accordance with the mechanism proposed here, an ATPase reaction could be associated to each reaction leading from a P, form to the following Pj+, form of the carrier.…”

“…In fact experimental data are complex (Hodges 1976), but some of them appear relevant to us. Thus in oat roots, within some phases, a linear relation is found between Mg^' *' uptake and ATP hydrolysis by Mg^'^-stimulated ATPase (Stok et al 1981). Still more relevant in respect to our model is the finding in the same system (Stok et al 1981) that high Mg" concentrations sometimes inhibit ATPase.…”

Experimental determination of magnesium isotope fractionation during higher plant growth

“…Several studies show that all the Mg taken up by plants was initially physically adsorbed on the negative charges located at the root surface (Komaï, 1962;Stok et al, 1981;Kelly and Barber, 1991). Magnesium adsorption on root surfaces may therefore play a key role in the "heavy" isotope composition of plants.…”

Phosphate Interaction with Uptake and Leaf Concentration of Magnesium, Calcium, and Potassium in Winter Wheat Seedlings

“…High levels of K and/or NH 4 -N decrease Mg and Ca uptake (Claassen and Wilcox, 1974) and K depresses the translocation of Mg and Ca from roots to shoots (Ohno and Grunes, 1985). Some studies on Mg and Ca uptake indicate that influx is passive, but that both elements are actively eftluxed (Macklon, 1975;Mack-Ion and Sim, 1976;Stok et al, 1981). Minotti et al (1969) treated intact wheat seedlings for 24 h with N0 3 -N salt solutions containing various cations as counterions plus CaS0 4 and found that Mg was the only cation eftluxed from the roots.…”