Manganese Absorption by Excised Barley Roots

Abstract

Abstract. Short-term absorption studies with 5-day-old excised barley roots revealed that the basic aspects of Mn absorption were similar to those of other metab-olically absorbed cations. Following an initial non-metabolic equilibration with the root, Mn was absorbed for several hours at a slower steady-state rate comparable to that of other inorganic cations. Complete or nearly complete inhibition of the steady-state phase by low temperature, dinitrophenol, and azide provides strong evidence that Mn transport into this tissue was metabolically mediated. Within limits, the rate of transport was strongly dependent upon the concentrations of Mn and the hydrogen ions in the ambient solution. Absorption increased rapidly with increasing concentrations of Mn up to 1 meq per liter. Above this concentration, the rate leveled off, apparently due to a saturation of the transport mechanism. Within the physiologioal pH range in which Mn is soluble (below pH 7), absorption increased greatly with decreasing hydrogen-ion concentration.Altho,ugh numerous investigations of ion uptake by excised root tissue have been conducted, relative:ly 1little attention has been given to Mn. In 1934, Laine (4) studied the absorption of Mn and other ions by decapitated roots of Phaseoluts multiflorus. Analyses of both the exudate and the roots revealed an accumu,lation and retention of Mn by the roots. Using slices of carrolt tissue, Stiles and Skelding (10) found that Mn uptake occurred in 29 distinct phases, a rapid initial uptake followed by a pro,longed slower absorption. This 2-step process, characteristic of the uptake of other cations, was in(terpreted as consi,sting of the usual nonmetabo,lic and metabolic phases, respectively. Su'bsequent experiments with red beet discs cionfirmed this interpretation (9). More recently, Page and Dainty (6) 'have reported -that the uptake of !Mn by excised oat rooits is nonmetabolic. Both the characteristic rapid initial uptake and the folllowing slower steadystate tuptake occturretd independentlly of metabolic .ac-tivity. 6.0 or greater, nylon bags containing analytical grade Bio-Rad AG1-X8 anion exchange resin in the OH-form were dipped into the solution (7). All salts used were chlorides of analyzed reagenit grade.At the end of the absorption periood, the roots were coillected on a nylon screen and washed by pouring 3 4liters of distilled water over them. After drying overnight at 700, the roots were digested in nitric and perchloric acids and diluited to 100 ml. 527 www.plantphysiol.org on May 11, 2018 -Published by Downloaded from

Differential Capacity for High-Affinity Manganese Uptake Contributes to Differences between Barley Genotypes in Tolerance to Low Manganese Availability

“…In our work, genotypic differences were repeatedly and reproducibly obtained within a few weeks when plants were grown at In addition to the HATS system, a LATS system was identified with a K m of 80 to 110 mM (Table II), approximately one-fourth of that observed for excised maize roots by Landi and Fagioli (1983). A similar K m value of 400 mM was reported for excised barley roots by Maas et al (1968). In all cases, the uptake rates facilitated by LATS would, within a few minutes, lead to Mn toxicity (Mn tissue concentration .150 mg Mn g 21 DW) if no system to mediate Mn efflux was present.…”

“…The high-affinity transport system (HATS) operates in the range of the low available Zn concentrations found in most soils and is therefore likely to be the predominant Zn 21 uptake system . Similar information does not exist for Mn influx, where the only kinetic data originate from old studies with excised barley or maize (Zea mays) roots at fairly high and nonphysiological Mn concentrations in incomplete nutrient solutions (Maas et al, 1968;Landi and Fagioli, 1983).…”

Calcium Uptake by Excised Maize Roots and Interactions With Alkali Cations

“…That is, Ca2+ was absorbed most rapidly from salts of rapidly absorbed anions-NO;-> Cl-= Br-> SO42-. The (10,16,19,20), was markedly inhibited by H1 in the pH range from 3 to 5. The uptake of Clwas also depressed in this range, but the effect of (11).…”

Influence of Calcium and Magnesium on Manganese Absorption

“…Trebi) were used in all experiments. The planits were growwn and the roots were prepared and treated as described previously (10). The experimlental temperature was 25 ± 0.50 and the pH was 5.0 ± 0.2 maintained by small additions of 0.1 N HCl.…”

“…In a previous paper (10), evidence was presented for the metabolic transport of Mn into excised barley roots. Absorption was relatively rapid and was affected bv concentration, pH, etc., much as that of other inorganic cations.…”