Effect of Metabolic Inhibitors and Temperature on Uptake and Translocation of ⁴⁵Ca and ⁴²K by Intact Bean Plants

Abstract

The dependence of Ca uptake and translocation by intact roots of Phaseolus vulgaris on concurrent root metabolism was investigated using 'Ca-labeled Hoagland solutions at one-half and one-twentieth strength (2.5 and 0.25 mM Ca'). Adsorbed and absorbed "5Ca fractions in the roots were distinguished on the basis of the time course of exchange with the outer solution. Uptake of '2K, of which the characteristics are better known, was measured for comparison. The absorbed 'Ca fraction showed a markedly nonlinear increase with time in contrast to the near linear increase in 'K. Exposure of roots to cyanide, arsenate, 2,4-dinitrophenol, or low temperatures caused only slight reductions in '5Ca absorption by roots, but significant reductions of 'K. In all treatments involving inhibitors and low temperatures, the translocation to shoots of both 'Ca and 'K was strongly inhibited. The conclusion that much of the absorbed "Ca fraction in the root tissue is taken up by processes which are not rate-limited by metabolism is discussed.The convention of dividing cations bound by roots into two fractions, adsorbed and absorbed, on the basis of the time course of uptake and exchange has proved convenient for the monovalent cations (4,9,24). The adsorbed fraction characteristically reaches equilibrium with the bathing solution within minutes and is independent of metabolic processes. This process is considered to represent a simple nonspecific ion exchange within cell wall surfaces. The absorbed fraction is characterized by a slower rate of increase which continues for many hours. It is not readily exchangeable with the outer solution and is dependent on concurrent metabolism. The absorbed fraction may represent a net increase in ion content of the tissue or, for roots which have reached dynamic equilibrium with the outer solution, may represent tracer influx. It is implicit that the absorbed ions are retained within protoplasts, although precise localization of the two fractions has rarely been attempted.The characterization of uptake and retention of Ca and other divalent cations has shown less uniformity than that for the monovalent cations. Although some studies have indicated a constant rate of absorption of Ca (9,14,19,25) Measurements of uptake of Ca and other divalent cations by plant tissues is often complicated by the relatively large fraction held on adsorption-exchange sites in cell walls (5,8,9,36). In experiments with labeled ions the usual procedure for displaying this has been to immerse the root tissue at the end of a 'Ca uptake period in an excess of unlabeled solution for 30 min to remove the fraction designated as adsorbed; the amount retained by the root has been considered metabolically absorbed by the root cells (8, 9). For the sake of comparing the present results with previous studies the above terminology and methods have been retained.In this paper we present observations on the uptake of 45Ca by intact bean plants under conditions similar to those used to display, by microautoradiography, the lo...

Evidence for Symplastic Involvement in the Radial Movement of Calcium in Onion Roots

“…In support of this idea, there are some reports that Ca 21 movement to the shoot is not correlated with the speed of the transpiration stream (Atkinson et al, 1992;Jarvis and House, 1970). Drew and Biddulph (1971) found that the passage of Ca 21 into the transpiration stream of bean (Phaseolus vulgaris) was reduced by cold temperatures and several metabolic inhibitors. Also, when the bathing solution contained a relatively low concentration of Ca 21 , the ion was concentrated in the transpiration stream.…”

“…In this study, when 45 Ca 21 was eluted from either intact or dissected segments, three compartments were distinguished. The fastest eluting of these was identified as the cell wall based on a comparison of its half-time (about 1 min) with literature data (Drew and Biddulph, 1971;Maclon, 1975;Rygiewicz et al, 1984;Peterson, 1987;Rauser, 1987;White et al, 1992;DiTomaso et al, 1993;Devienne et al, 1994;Kronzucker et al, 1995aKronzucker et al, , 1995b and its lack of change during elution at cold temperature. A surface film, which would have eluted more rapidly than the wall compartment, was not evident.…”

The kinetics of calcium and magnesium entry into mycorrhizal spruce roots

“…Therefore, a strong temperature dependence would be a good indication of a symplasmic transport of the ion under study. There are several examples where ion uptake and transport into roots were reported to be temperature-dependent (see Johnson and Jackson 1964;Drew and Biddulph 1971;Schimansky 1981). In the kinetics of Mg and Ca, we ®nd no such eect, with the exception of the small initial increment already discussed above.…”

The Accumulation and Transport of Calcium in Barley Roots

“…1965). The movement of Ca from roots to shoots was inhibited by DNP and low-temperature treatments applied to roots (Drew and Biddulph 1971). These results suggested that a metabolic process was responsible for the movement of Ca.…”