Hori, Shiro

Kawasaki, Toshio

Okayama University Digital Information Repository

THE ROLE OF CALCIUM IN THE SELECTIVE CATION UPTAKE BY PLANT ROOTS I. Effect of Cation Concentrations in Absorption Solution*

Okayama University Scientific Achievement Repository

THE ROLE OF CALCIUM IN THE SELECTIVE CATION UPTAKE BY PLANT ROOTS 1. Effect of Cation Concentrations in Absorption Solution本Tc渇hioKA WASAKI and Shiro HORI帥It is well known that th~ 田l民tive mechanism is involved in the ion uptake prα:es by plant roots. However， ithas been very diffiωlt to explain how living cells discriminate between such similar ions as potassium and sodium. Viets (28) showed that the uptake of potassium and bromide by barley r'∞ts were stimulated in the pre田nceof calcium and other polyvalent伺 tions.The role of calcium in the ion uptake pr'∞回shas been studied by several groups of worker宮町田Viets'report.白1the stimulation of ion uptake by calcium， various explana-tions were p民間ntedin relation to carrier theory (4， 8， 15， L6， 18， 20， 25) or stability of carrier substanc回 (5，9， 23). The importance of calcium on the permeability of cel membran回 wasindicated in記 veralexperiments which were conducted by the u民 ofchelating agents， ribonuclease and ultraviolet radiation (5， 9， 23， 24). Further， ithas been noted that the effect of calcium on the ion transport is not only stim由 tive，but also inhibitory (6， 7， J 2， 17). R悶 ntly，Jacobson et al. (13， 14)， E戸teinet al. (3， 22)組 dWaisel (29) showed that calcium was e蹴 ntialfor integrity of the selective ion transport m配hanism，and that the role of calcium was involved in the regulation of cel permeability for various ions. In the cou白eof studies of such calcium effect， however，回mer，回叫ts∞n-flic也19with the民:portby Viets were shown on the substitution of magn田iumfor calcium (3， 10). On the other hand. there were田mereports in which it was 叩回目制thatthe calcium effect d蹴 ribedabove was not caused by回lcium，but caused by ac∞mpanying anions，白戸到c:iallychloride (21， 26). The pre記ntinv田ti-gation was initiated in order to clarify th田econflicting and obscure r，回ults.More-over， an approach was attempted to obtain further informations on the role of calcium in the selective uptake pr∞ess of rubidium and sodium. MATERIALS AND METHODS Preparation 01 Root Materials Excised r'∞ts of barlay (Hordeum vulgare L.， variety Akashinriki) were used in this inv白tigation. The me出odof culturing was similar to that d舵 ribedby Epstein et al. (1， 2). Seeds of barley we回 allowedto germinate for 24 hours in * Main }:岨rtof this paper was published in Joumal of the Science of sc元1and Manure， Ja戸n，Vol. 39， p.433-438 (1968)， inJapanese. 特Depar回阻tof Applied Biology， Radiation Center of 0担 knPrefecture. 124 T.Kaw乱saki& S. Hori aerated water in the dark at 250C. The germinating s伺 dswere sp回adon a layer of plastic screen about one centimeter above the surface of O. 1 mM calcium sulfate solution. The as記mbly(figure 1) was placed in the dark at 250C. Theω，lution ~Air Fig. 1. Culture assembly for y'∞ng barley plants. was aerated continuously， and renewed 3 days after the start of the growth 戸n吋s.When the plants were 5 days old， the roots we民 excisedjust below the scr，田n，thoroughly washed with demineralized water， and centrifuged for 5 minut回 atabout 65 x 9 to remove the adhering water (14， 18， 19). Absorpt;on Exper;ments In orderωmv田tigatethe sel配 tiveuptake betw田nrubidium and s吋ium，equimolar mixtur，田ofrubidium chloride and sodium chloride we回 employedas absorption solutions with or without addition of calcium chloride or magn回i田nchloride. Initial pH of 油田rptionsolutions was adjusぬdt05.5:t0.1. Forthe up匂kemeasurements of rubidium or回dium，the absorption solutions were labeled with radi伺 ctiverubidium (88Rb) or radioactive sodium e別a).In al experiments， 0.5gofr∞ts were u田din 500ml of 油田rpiI>∞solution.Absorption period was 60 minutes， and the solutions were∞ntinuously aerated and kept at 25土0.10Cor 2:t 0.5 oC during this time. At the end of the absorption period， the r∞ts were separated from the solution with a nylon mesh filter. For removing adheringωlution， the 1∞ts were blotted with filter paper， shaken for 30 seconds in 30 ml of demineralized water， and this washing operation of r∞ts was re戸atedonce more. Radioactive Assay The r，∞t回mpl田 weredried， and ashed at 450oC. One ml of dilute hydr。125 chloricacid鉛，lutionwas added to the ash and the回mpl田 we問 driedunder infrared lamp. Then， the阻mpl田 were∞untedwith a Geiger-Muller ∞unter. Role of Calcium in Selective Cation Uptake RESULτ's Effect 01 Dillerent Concentrations 01 Monovalent Cations in Absortトtion Solution The uptake of rubidium and S(対iumby excised barley 1'(沿tswe問 investigatedunder wide∞n田ntrationrange of monovalent cations in ab釦 rptionsolution. The lowest concentration of monovalent cations was 0.0001 m M and the highest was 10.0 mM. Two levels of divalent cations we民 u鈴dat 0.05 and 0.5 mM. The rate of rubidium uptake at 0.05 m M of divalent cations is shown泊fi思ue2， and the rate of sodium uptake in figure 3. Besides， the rate of rubidium uptake at 0.5 mM ofdivalent cations is shown in figure 4， and the rate of sodium uptake in fi肝問5. Both the ordinate and the absci掛 valu回 infigu詑s2to5arelogarithmic. As shown in figur回 2and 4， the rate of rubidium uptake represented the curv回 whichwere characterized by st田pslope at lower concentration range followed by gentle slope at higher ∞ncentrati∞range， at both 25 and 20C; in other words， the rate of rubidium uptake was linear with increasing concentrations 25・c10.0 1.0 0.1 2・c0.01 No addition CaCl2 MgC12 。• 0.001 ?????? ? ??? ?? ???'‘ 0.0001 External concen位置tionof monov直l阻 tcations， mM Fig. 2. Rubidium uptake in relation to external∞n国 ltrationof monovalent cations in the absence and pre世nceof 0.05 mM of divalent回 tio田 .10.0 1.0 0.1 0.01 0.001 0.0001 T.Kaw醐 ki& S.Hori 10.0 0.01 1.0 0.1 ????????????????126 0.001 宙線 MgCI20.0001 0.001 0.01 0.1 1.0 10.0 Extemal ∞n倒 ltrationof monovalent cati，∞5， mM Fig. 3. Sodium uptake in relation to位同nal悶 lcentrationof monovalentωtions in也eabsence and pr間 nceof 0.05 mM ofdivalent αtions. 0.0001 ? ? ? ? ?? ? ??? ? ?10.0 1.0 0.1 2.'C No addition CaCb MgCh 。• ??????? ? ???』?? ? ???0.01 0.001 lC 0.0001 0.001 0.01 0.1 1.0 10.0 Ext，位nal∞ncentmtionof monovalent cations， mM Fig. 4. Rubidium uptake in re凶 onωextemal問問n回 tionof monovalent伺 tionsin the absence and pr'白田ceof 0.5 mM ofdivalent cations. 0.0001 127 Rale of Calcium in Selective Cation Uptake ????????10.0 1.0 0.01 0.001 0.1 ??????????? ? ???0.0001 0.001 O.QI 0.1 1.0 10.0 Extemal側四n岡山nof monovalent catiOll8， mM Fig. 5. 50:対iumuptake泊 relationto externalαmcentration of monovalent αtions in the al班 nceand pr間 nceof 0.5 mM ofdivalent ca出ns.0.0001 of monovalent cations at lower range， and then remained plateau at higher range. Hence， it was considered that rubidium uptake was dependent on the concentration h油田中tionsolution at lower range and relatively independent at higher range. By contrast， fig1.江田 3and 5 showed that the rate of反対iumuptake represented the curv田 whichwere characterized by steep slope over al concentration range u田din this experiment at both 25 and 20C， i.e.， 双対iumuptake was dependent on the concentration in absorption田.lutionover al concentration range. As can be seen through figures 2 to 5， the rate of rubidium uptake was decreased in the pr'白 enceof divalent cations at lower concentration r釦 geof monovalent cations. Similarly， the rate of反対iumuptake was d配r田島din the pr.間 n伺 ofdivalent cations over al concentration range of monovalent cations. on the other hand， at higher ∞ncentration range of monovalent cations， itwas likely出atthe rate of rubidium uptake was increased in血epresence of calcium chloride at 250C， while the rate of rubidium u開法ew田 d配 r回 sed白血epr蹴 nぽof divalent cations at 20C. Such eH配 tsof calcium and magn白lum回ltson the uptake of monovalent cations were larger at 0.5 mM ofextemal concentration than at 0.05 mM. Further investigation w出 undertakenon the effect of divalent cations on rubidium and反泊iumuptake. T.Kawa叫d& S.Hon Effect of Different Concentrations of Divalent Cations in Absorttion Solution 128 The uptake of rubidium and sodium were inv白tigatedat various concentra-tions of divalent cations. Two levels of monovalent cations were used at 0.001 and 1.0 mM. The rate of rubidium uptake at 0.001 and 1.0 mM ofconcentra-tions of monovalent cations is shown白戸rcentageto the ∞ntrol without addition of divalent伺 tionsin figt江田 6and 7， r田pectively.The rate of sodium uptake at 0.001 and 1.0 mM ofconcentrations of monovalent cations is shown in the回 memanner in figt江田8and 9， r四戸当ctively.All experiments in this part were carried out at 250C. Figur，回 6and 7 showed that， as the ∞ncentration of divalent cations in-crea田d，the rate of rubidium uptake was d配 r聞記dat 0.001 mM ofmonovalent 伺 tions，but the rate of rubidium uptake w田 increasedat 1.0 mM ofmonovalent cations. The increase of rubidium uptake was larger in the presen白 ofcalcium % 100 50 ??』??????0.05 0.1 0.5 1.o .0.05 0.1 0.5 1.0 CaClz MgClz A剖itionof divalent cati岨s，mM Fig. 6. Effect of various con閣官叫onsof divalent ca出，nson ru凶 iumuptake from ab抱'rptionsolutions c阻組iningO.∞1 mM of mono羽 lentcatio凶， at 250C. 。r-% 100 u ，国呈ロA E同 50 o 005 0.1 0.5 1o 0.05 0.1 0.5 』ー 目ー ーー 『ーー -CaClz MgCl2 Addition of divalent catiOl:l， mM Fig. 7. Effect of vanous倒 lcen回 tionsof div芭lentcations on rubidium uptake from absorpti∞ぬ，lutionsωntai凶ng1. 0 mM ofmono咽 lentca白幽， at 250C. 1.0 Role of Calcium in Selective Cation U戸akei % 100 岩 50o 005 0.1 0.5 1.0 0.5 0.1 0.5 1.0 CaCI% MaCl Addi出nof divalent cations， mM Fig. 8. Effect of various αmce泊trati∞Sof divalent cations on sodium uptake from absorptionぬ，lutionscontaining 0.001 mM of monovalentαtions， at250C. 也..>1 g 0. ロ咽% 100 Z 50 o 0.05 0.1 0.5 1.0 0.5 0.1 0.5 1.0 CaCI2 MgCI2 Addition of divalent cations， m M Fig. 9. Effect of various concentrations of divalent cations on sodium uptake from absorption solutions∞n凶ning1. 0 mM ofmonovalentαtions， at250C. 129 chloride白血 inthe pr蹴 nceof magn回iumchloride at the回meconcentration. Figt江田 8and 9 showed that， as the concentration of divalent cations increased， the rate of釦 diumuptake was d配 r伺 sedat bo出 0.001and 1.0 mM ofmonovalent catlons. DISCUSSION Overstreet et a1. (20) showed出atcalcium exerted both depr，鰯ingand stimu-lating eff配 ton the 油田rptionof potassium and that the effects were rela鈴dto the ∞n叩 ntrationof potassium in absorption釦 lution. Here， itwas evident that the rubidium uptake was stimulated in the pre舘 nceof divalent cations at higher concentration of monovalent cations (figure 7). On the other hand， the rubidium uptake was inhibited in the pr鵠enceof divalent cations at lower concentration of monovalent cations (fi伊 re6). The sodium uptake was inhibited in the pr田enぽof divalent cations at both higher and lower concentrations of monovalent cations (figures 8 and 9). Thus， the ∞ncentration range in which the uptake of both 130 T.Kawa銘記&S.Hori rubidium and sodium were inhibited in the pre記nceof divalent cations ∞incided with the steep slope range of monovalent伺 tionuptake curve. The uptake of rubidium and釦 diumat st田 pslo戸 rangewere governed by the concentration of monovalent cations in 油田rption田lution. A，∞ordingly， itwas sup伊sedthat divalent伺 tionsinhibited the uptake of rubidium and s吋iumunder such conditions 出atnonmetabolic factor was predominant on the ion uptake proc田s，叩dthat divalent cations stimulated the uptake of rubidium under such conditions that metabolic factor w舗 predominant. A hypo品目isd回cribedabove w部 furtheremphasized by the fact that the stimulating e丘町tof divalent cations on the rubidium uptake w部 temperature-dependent(figure 4). It was thought that the stimulating effect of calcium on rubidium uptake might be located in the metabolic pr民側 ofion uptake. Fu吋leロnore，it was evident出atmagnesium chloride ∞uld be used to substitute for calcium chloride in relation to stimulating on出erubidium uptake (figure 7). However， the stimulating eff配ton the rubidium uptake was clearly larger in血epr'蹴 nceof calcium chloride than in the pre田n田 ofmagn田iumchloride at出esame concentration of absorption solution. As the molar concentra-tion of calcium chloride was equal to the molar concentration of magn田 iumchloride， bo也 t民atmentswi出 calciumchloride and magn白iumchloride were equal in the amount of chloride in absorption田，lution. A，∞ordingly， itw酪 clearthat the stimulating effect of calcium chloride on the rubidium uptake w田 mainlyowing to calcium， but not chloride. SUMMARY The selective 油田rptionof rubidium and sodium from equimolar mixture of rubidium chloride and sodium chloride was studied with relation to addition of calcium chloride or magn回i山nchloride. 1) The rate of rubidium uptake repre記ntedthe curves which were charac-teri詑dby steep slope at lower concentration range followed by gentle slope at higher ∞ncentration range. The rate of sodium uptake repr蹴 ntedthe curves which were characterized by steep slope over a1 concentration range used in this experiment. 2) At lower concentration of monovalent cations in absorption solution， rubidium uptake decreased in the presen白 ofcalcium chloride or magn田iumchloride. Similarly， at lower and higher ∞ncentration of monovalent cations in absorption回 lution，反対iumuptake d配 reasedin the pre記nceof calcium chloride or magn田iumchloride. 白1the other hand， at higher ∞ncentration of monovalent cations in absorp-tion田lution，rubidium uptake increa民din the presen田 ofcalcium chloride or magnesium chloride. The stimulation of rubidium uptake by calcium chloride w酪larger than the stimulation by magnesium chloride. 3) The r，白ultsobtained support that the stimulating e紅白tof calcium chlo-Role of Calcium in Selective Cation Uptake 131 ride on rubidium uptake is caused by calcium， but not by chloride. Then，出estimulating effect of calcium on rubidium uptake could be partially substituted with magnesium chloride. 4) It was su回目tedthat the stimulation of calcium on rubidium uptake might be located in the metabolic process of ion u酔ake.REFERENCES 1. E戸tein，E. and Hagen， C. E. 1952. A kinetic study of the absorption of alkali cations by 凶rleyr∞ts. Plant PhysioI. Zl: 457-474. 2. Epstein， E.and Leggett， J.E. 1954. The absorption of alk且line伺 rthcations by barley r∞ts: Kinetics and mechanism. Am. J. Botany 41: 785-791. 3. E~回tein， E. 1961. The偲sentialrole of calcium in sel舵tive白血n回 nsportby plant cels. Plant Physiol. 36: 437 -444. 4. Fawzy， H.， ov位前向et，R. and Ja∞Ibson， L.1954. 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THE ROLE OF CALCIUM IN THE SELECTIVE CATION UPTAKE BY PLANT ROOTS I. Effect of Cation Concentrations in Absorption Solution*

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