Absorption of Magnesium and Chloride by Excised Corn Root

Abstract

Leggett and Gilbert (8,9), and Johnson and Jackson (5) show that excised roots of barley, soybeans, and wheat, respectively, all actively accumulate Mg2" but accumulate very little Ca2`.Nevertheless, Ca2+ may markedly affect the absorption of Mg'+.Without being absorbed itself, CaY+ greatly inhibits the uptake of Mg2" by barley roots (7,15). However, this effect does not appear to be universal, as CaY+ reduces Mg'+ uptake only slightly in soybean roots (9). These divergent effects of CaY+ certainly warrant further study. Furthermore, the nature of the interaction between CaW+ and Mg2" might be better understood if studied with a species that absorbs both CaY+ and Mg". One species that meets these requirements is corn. Unlike the plant tissues mentioned above, excised corn roots actively absorb CaW+ (3, 10), as well as Mg'+. This study was undertaken to characterize the general features of Mg2`and Cl-uptake by this tissue and to determine the effects of Ca2+ under various treatment conditions. MATERIALS AND METHODSExperiments were conducted with 6-cm apical segments of primary corn roots (Zea mays, cv. DeKalb 441). The roots were obtained from 5-day-old seedlings that were dark-grown in 0.2 mi CaSO, according to the procedure described previously (10). The preparation and treatment of the roots are also indicated therein, except for the following minor modifications: (a) to minimize leaching of the excised roots prior to treatment, the roots were held between several layers of damp cheesecloth rather than in distilled water and (b) both growth and treatment temperatures were maintained at 30 C, except when temperature was a variable. A root to solution ratio of 1 g/liter was used in all treatments except when MgCl, concentrations were less than 0.1 meq/liter in which case a ratio of 1 g/4 liters was used. The absorption solutions were aerated continuously and the pH was controlled within +0.2 unit with acids or bases corresponding to the ions in the solutions.Treatments were terminated by removing the roots from the absorption solution and rinsing them for 30 sec in 1 liter of distilled-deionized water. Chloride was extracted from the fresh roots with four successive 10-ml aliquots of boiling water and was determined by automatic coulometric-amperometric titration (1). The hot water extracts and titrated solutions were then recombined quantitatively with the root samples, taken to dryness, and digested in nitric and perchloric acids. Cations were determined by atomic absorption spectroscopy. Initial contents of Mg2', Ca2 , Cl1, and K+ were about 4, 6, 6, and 28 ,ueq/g fresh weight, respectively. With the exception of the time course experiment, all the absorption data were obtained from two treatment times of 1 and 5 hr and are expressed as absorption rates (/eq/g fresh roots per hr Figure 1, steady state rates prevailed from time zero up to 6 hr and decreased appreciably thereafter. At the pH employed, 5.6, Mg`uptake exceeded that of Cl-at both concentrations. The relative rates of Mg2+ and Cl-absorpti...

Competitive Al3+ Inhibition of Net Mg2+ Uptake by Intact Lolium multiflorum Roots

“…Experiments with KCN added to the nutrient solution ofthe depletion experiment gave the results that were essentially the same as those obtained with CCCP (data not shown). Energy dependence of Mg2' uptake has been shown earlier in work with excised roots (19,21). In addition, a nonactive component of Mg2' uptake that was not transpiration dependent is suggested in the present study (Fig.…”

“…Net Mg2" uptake ( Fig. 1) appeared to show characteristics ofdiscontinuous, saturable carrier-mediated transport, as was also shown earlier for net Mg2" uptake (14,19,21) as well as for Mg2' influx (13).…”

“…of net Mg2' uptake, indicating noncompetitive inhibition. A decrease in Mg2+ uptake due to low solution pH has been previously observed (13,19,21).…”

Mg and K effects on cation uptake and dry matter accumulation in tall fescue (Festuca arundinacea)

“…Maas and Ogata (1971) reported Mg absorption rates in corn (Zea mays L.) roots in the range of 560 to 830 nmol kg −1 s −1 . These higher Mg inflow rates in wheat and corn may be due to their higher transpiration rates.…”

Transport of magnesium ions in the phloem of Ricinus communis L. seedlings

“…The uptake of magnesium by roots is strongly suppressed by some cations (Moore et al 1961;Maas and Ogata 1971 ;Claassen and Barber 1977;Heenan and Campbell 1981;Marschner 1986). We therefore tested whether cations also affect phloem loading of magnesium.…”