Active Transport of Ions across the Root of Ricinus communis

The electrical potential difference between the exuding sapof detopped castor oil plants and the external I mM KC1 bathingsolution has been measured, together with the concentrationsof potassium and chloride. A typical value for the electricalpotential of the sap with respect to the external solution was—56 mV, while the sap concentrations of potassium andchloride were 8 mM and 3.5 mM respectively. The total cationconcentration, made up of K, Na, Ca, and Mg, was about Io m.equiv.1.;the anion deficit is made up by SO₄, NO₃, and PO₄. A comparisonof the measured potential difference with the Nernst potentialsfor potassium and chloride suggests that the movement of potassiuminto the sap is a passive process while the movement of chlorideis an active process against the electrochemical potential gradient.It is suggested that the potassium and chloride ions pass throughthe diffusion barrier at which active transport takes placebefore they exchange with the other ions which appear in thesap. On the basis of this assumption it is shown that potassiumis close to passive equilibrium while chloride is accumulatedagainst an electrochemical potential difference of 110 mV or2, 500 cal.mole^–1.     

Electrical Potentials and Na, K, and Cl Concentrations in the Vacuole and Cytoplasm of Nitella translucens

The potential differences across the tonoplast and plasmalemmamembranes have been measured in the single cells of Nitellatranslucens, the cells being immersed in an artificial pondwater (composition: NaCl _1.0 mM., KC1 _0.1 mM., CaCl₂, _0.1 mM.).The potential of the cytoplasm is –138 m V with respectto the bathing medium and –18 mV with respect to the vacuole.The concentrations of Na, K, and Cl have been measured in thetwo cell fractions. The concentrations in the flowing cytoplasmare: Na 14 mM., K 119 mM., and Cl 65 mM.; the vacuolar concentrationsare: Na 65 mM., K 75 mM.,and Cl 160 mM. The observed potential differences across the two membranesare compared with the Nernst potentials for all three ions.This analysis shows that all three ions are actively transportedat the plasmalemma: Na is pumped outwards while K and Cl arepumped inwards. At the tonoplast Na is pumped into the vacuolewhile K and Cl are close to electrochemical equilibrium. The inhibitor, ouabain, has no effect on the cell resting potential.     

Asymmetrical neural cross-adaptation of hamster chorda tympani responses to sodium and chloride salts

Cross-adaptation has occurred when exposure to an adapting chemicalstimulus (A) reduces the response to a subsequent test stimulus(B). The degree of cross-adaptation between two stimuli is thoughtto reflect the overlap of their ‘neural activation processes’.We measured self- (A—A) and reciprocal crossadaptation(A—B, B—A) of the response of the hamster chordatympani nerve with lingual presentations of stimuli elicitingequal unadapted transient responses. Adapting and test stimuliwere 0.1 M NaCl, 0.1 M NaNO₃, 0.1 M NaBr, 0.4 M Na acetate (NaAc),0.09 M LiCl and 0.4 M NH₄Cl. Nearly complete and symmetricalcross-adaptation was seen for NaCl, NaNO₃ and NaBr. Those Nasalts paired with LiCl showed strong but asymmetrical cross-adaptation.Exposure to sodium completely eliminated the response to LiClbut not vice versa, suggesting that lithium and sodium are notcompletely interchangeable taste stimuli for the hamster chordatympani. Relatively little cross-adaptation between NH₄Cl andother salts suggested relatively separate neural activationprocesses. Strongly asymmetrical cross-adaptation was foundbetween NaAc and the other sodium salts. Responses to NaCl,NaNO₃ or NaBr were eliminated after adaptation to NaAc whereasthe response to NaAc during the reciprocal cross was strong.Asymmetries are discussed in reference to sensitivities of singlenerve fibers for the chorda tympani, effects of adaptation andthe concept of anion inhibition.     

Phloem and Xylem Transport in the Supply of Minerals to a Developing Legume (Lupinus albus L.) Fruit

The economy of carbon, nitrogen, water and mineral elementsin fruits of Lupinus albus L. was studied by measuring accumulationof these quantities in the developing fruit and estimating itstranspirational losses and CO₂ exchanges. Combining this informationwith data on levels of mineral elements in the xylem sap andphloem sap supplying the fruit, it was possible to test whethertransport based on mass inflow through xylem and phloem wouldaccount for the observed intake of elements. A model of transportbased on water and carbon intake suggested that vascular intakeduring the fruit's life matched the recorded increment for mineralsto within ± 15 per cent for N, Na, Zn, Fe and Cu, andto within ± 23 per cent for P, K and S. However, estimatedvascular intake of Ca, Mg and Mn accounted for less than one–thirdof the recorded intake by the fruit, inadequacy of vascularintake being especially great early in growth. Transport inphloem accounted for more than 80 per cent of the fruit's vascularintake of C, N and S, and 70–80 per cent of its P, K,Mg and Zn. Xylem contributed 68 per cent of the vascular inputof Ca, 59 per cent of the Na, and 34–38 per cent of theFe, Mn and Cu. Enclosure and darkening of fruits reduced levelsof Ca and Fe but increased levels of N, P, K and Zn in fruitdry matter relative to unenclosed, illuminated fruits. Resultswere related to previous observations on fruit functioning. Lupinus albus, legume fruit, mineral supply, phloem, xylem     

Mineral nutrition, of cultured chlorophyllous cells of tobacco VII. Effects of the NH4/NO3 ratio and of Cl in the media on the growth and ionic balance of cells

NG, a strain of cultured tobacco cells of Nicotiana glutinosahad high growth rates and carboxylate contents (C—A) of100 to 130 meq/100 g of dry cells on media containing 42 meqNO₃/liter as the sole N source. (C—A) is the amount ofinorganic cations minus inorganic anions in meq per 100 g ofdry cells. NG, cultured on media containing NH₄ 10+NO₃ 42 in meq/liter,had lower growth rates and lower (C—A) values as comparedwith NG on media containing NO₃ as the sole N source. NG, cultured on media containing NH₄ 30+NO₃ 42 in meq/liter,had high growth rates and (A—C) values of 22 to 53 meq/100gof dry cells. In this case, the (A—C) content may correspondto organic cations, basic organic N compounds such as free asprotein-bound basic amino acids. The easily absorbed Cl mayhave been required maintain good growth conditions such as ionicbalance and a favorable pH in the cells. Thus cultured cells of Nicotiana glutinosa may have physiologicaladaptability against variations in a relatively wide range of|C—A| contents [|C—A| being the absolute valuesof (C—A)]. (Received May 15, 1980; )     

Major Element Composition of Epidermal and Mesophyll Tissues2Commelina Communis L. and Vicia Faba L.: Some Further Considerations of the Role of Ions in Stomatal Functioning

Epidermal and mesophyll tissues of Commelina communis L. andVicia faba L. were analysed by atomic absorption spectrometryfor the major plant inorganic cations and anions (K, Na, Ca,Mg, P, NO₃-N, Cl) when stomata of the leaf were open and closed.Water-soluble and residual levels of the elements were estimatedand a charge balance of the soluble fraction made. The major portion of K, Na, Cl, and P was extracted in the water-solublefraction of the epidermal and mesophyll tissues of both species.In both species the bulk of Ca remained in the insoluble residueof the epidermis whereas in mesophyll tissue it was equallydistributed be-between the two fractions in C. communis butmainly in the insoluble residue in V. faba. Magnesium was predominantlyfound in the water-soluble fraction of V. faba mesophyll tissueand distributed approximately equally between the two fractionsin the epidermal tissue. In C. communis Mg was slightly moreabundant in the water-soluble fraction of both mesophyll andepidermis. In both species no statistically significant differences inthe levels of the elements could be detected between epidermaland mesophyll tissues from leaves with open stomata and thesame tissues from leaves with closed stomata, suggesting thatthere was no major flux of ions between mesophyll and epidermisduring stomatal movements. Regardless of whether the stomata were open or closed, therewere considerably more water-soluble inorganic cations thananions present in all tissues of both species with K being themajor cation and Cl being the major anion. In V.faba and C-communis epidermis there was 49–53 per cent and 56%68per cent excess cation respectively. In the mesophyll tissuethe excess cation was 63–75 per cent and 75%78 per centin V.faba and C. communis respectively. When the partitioning of the levels of the elements betweenepidermis and mesophyll of a leaf is considered, except forNO₃-N in both species and Na in V. faba, 20 per cent or lessof each element was present in the epidermis.     

Ion Distribution in Salt-stressed Mature Zea mays Roots in Relation to Ultrastructure and Retention of Sodium

Ultrastructural features and the distribution of soluble ionshave been examined in mature roots of Zea mays plants grownin both NaCl and Na₂SO₄ salinities. When the plants were grown in either salt, the Na concentrationincreased proximally along the root with a concomitant declinein the K concentration. Both trends were reversed in the shoot. X-ray microanalysis of deep-frozen, fully hydrated specimensshowed that in salt-treated roots Na, and Cl, or S were distributedabout stoichiometrically in the cortex and endodermis. Na wasusually less concentrated than the anion in the lumens of thevessels, but was concentrated markedly relative to either Clor S in the adjoining xylem parenchyma cells. In the older, proximal parts of seminal roots of plants grownboth without salt (controls) and in the presence of either NaClor Na₂SO₄, wall developments occurred in xylem parenchyma cellsat the half-bordered pits in which the cell wall became markedlythicker and possessed a loosely packed fibrillar structure.These structures were not comparable with the transfer-celltype of protuberances reported in the roots of other species. In the xylem parenchyma of plants grown in the presence of Na₂SO₄there were dramatic increases in the quantities of rough endoplasmicreticulum, ribosomes, and mitochondria relative both to controlsand NaCl treatments. The results are discussed in relation to the possible functionof the xylem parenchyma of the mature root in the reabsorptionof Na from the xylem sap, which may mitigate adverse effectsof salinity in salt-sensitive glycophytes.     

Cation distributions across the larval and pupal midgut of the lepidopteran, Hyalophora cecropia, in vivo.

1. The levels of potassium, sodium, magnesium and calcium in leaves, midgut contents, midgut tissue, and blood were analysed in seven developmental stages between feeding, fourth-instar larvae and new pupae of the Cecropia silkworm. 2. Three dramatic changes in cation levels were found: the K level in the contents drops from 284 /+- 51 mEquiv./1 tissue water in the fifth-instar larva to 51 +/- 6 mEquiv./1 in the new pupa; the Mg level in the midgut tissue increases from 28 +/- 3 mEquiv./1 at the time of gut evacuation to 1093 +/- 104 mEquiv./1 in the new pupa; and the Ca level in the contents drops temporarily from 56 +/- 12 mEquiv./1 in the feeding fourth instar larva to 17 +/- 5 mEquiv./1 in the new fifth instar larva. The Na level was nerve higher than 2.8 +/- 0.5 mEquiv./1. 3. The relative levels of the four cations were different for each tissue studied, but each tissue maintained the same relative levels during the developmental stages studied. The sequences are: leaf, Ca greater than K GREATEr than Mg greater than Na; midgut contents, K greater than Ca greater than Mg greater than Na; midgut tissue, K GREATEr than Mg greater than Ca greater than Na; and blood, Mg greater than K greater than Ca greater than Na. 4. There were three large concentration gradients across the midgut; the K level in the midgut contents is approximately 10 times the level in blood; the Mg level in contents is one-half to one-sixth the level in blood; and the Ca level in contents is 3-4 times the level in blood. The K gradient and the Ca gradient are opposed and the Mg gradient is favoured by the electrical gradient across the larval midgut, the contents being 100 mV positive with respect to the blood. The K gradient and the electrical gradient are not present across the pupal midgut while the Mg gradient and the Ca gradient persist. 5. The K gradient is presumably maintained by the midgut K pump, the Mg gradient is aided by the midgut Mg pump, and the Ca gradient suggests that the midgut may possess a Ca pump.     

Learned aversions and taste qualities in hamsters

Interralations among taste perceptions in gloden hamsters (Mesocricetusauratus) were examined using generalizaions of learned tasteaversions. If stimulus A is avoided given a taste aversion hasbeen established to stimulus B, and vice versa, A and B ‘cross-generalize’.Stimuli within five groups cross-generalized. The groups ofcompounds were (i) sweeteners (fructose, saccharin, sucrose);(ii) sodium salts (NaCl, NaNO₃, Na₂SO₄): (iii) non-sodium salts(KCl, MgSO₄ NH₄Cl) plus quinine HCl; (iv) acids (acetic, hydrochloric,citric); and (v) urea. Only two pairs of stimuli from differentgroups cross-generalized (HCl—NH₄Cl. quinine HCl—urea).Neural patterns of response recorded form chorda tympam nervefibers in hamsters suggest that taste receptors on the anteriortongue distinguish among three groups of taste stimuli: sweeteners,sodium salts, and a group including non-sodium salts, acids,quinine HCl and urea. Neurons innervating other taste fieldsare likely to provide the information that hamsters use to discriminateamong the tastes of non-sodium-salt and non-sweetener stimuli.     

Ionic Interactions of Petiole and Lamina During the Life of a Leaf of Castor Bean (Ricinus communis L.) Under Moderately Saline Conditions

Ion (K⁺, Na⁺, Mg²⁺, Ca²⁺ and Cl) flows and partitioning in thepetiole and lamina of leaf 6 of castor bean {Ricinus communisL.) plants growing in the presence of a mean of 71 mol m^–3NaCl were described by an empirical modelling technique. Thiscombined data on changes in ion contents of petiole and lamina,ion: carbon molar ratios of phloem bleeding sap and pressure-inducedxylem exudates of the leaf with previously described informationon the economies of C and N in identical leaf material. Datawere expressed as daily exchanges of ions in xylem and phloem,or depicted as models of ion balance and transport activityof petiole and lamina during four consecutive phases of leaflife. The early import phase was characterized by high intakeof K and Mg through phloem, and of Ca mainly through xylem,but only limited intake of Na and Cl. The next phase up to fullleaf expansion showed similar relative differences in xylemintake between ions and the onset of rapid phloem export fromthe lamina of K and Mg, some export of Na and Cl but scarcelyany of Ca. The next mature phase, marked by maximal photosynthesisand transpiration by the leaf, showed high xylem intake of allions in xylem. This was more than matched by phloem export ofMg and K, but by only fractional re-export of Na and Cl andagain very limited cycling through the leaf of Ca. The finalpre-senescence phase exhibited similar behaviour, but with generallygreater contribution to phloem transport from mobilization ofion reserves of the lamina. The petiole retained particularlylarge amounts of Na and Cl in its early growth, thereby protectingthe lamina from excessive entry of salt, but these petiolarpools, together with those or other nutrient ions, were laterpartially mobilized to the lamina via the xylem stream. Datawere discussed in relation to the relatively high salt toleranceexhibited by the species. Key words: Ricinus communis, xylem and phloem transport, ion balance, K+ economy, Na+ exclusion, NaCl-stress, salt tolerance, leaf development     

Airway surface fluid volume and Cl content in cystic fibrosis and normal bronchial xenografts

We describe theuse of an in vivo human bronchial xenograft model of cystic fibrosis(CF) and non-CF airways to investigate pathophysiological alterationsin airway surface fluid (ASF) volume (V_s) and Cl content.V_s was calculated based on thedilution of an impermeable marker,[³H]inulin, duringharvesting of ASF from xenografts with an isosmotic Cl-free solution.These calculations demonstrated thatV_s in CF xenographs (28 ± 3.0 µl/cm²;n = 17) was significantly less thanthat of non-CF xenografts (35 ± 2.4 µl/cm²;n = 30). The Cl concentration of ASF([Cl]_s) wasdetermined using a solid-state AgCl electrode and adjusted for dilutionduring harvesting using the impermeable[³H]inulin marker.Cumulative results demonstrate small but significant elevations(P < 0.045) in[Cl]_s in CF (125 ± 4 mM; n = 27) compared with non-CF(114 ± 4 mM; n = 48) xenografts.To investigate potential mechanisms by which CF airways may facilitatea higher level of fluid absorption yet retain slightly elevated levelsof Cl, we sought to evaluate the capacity of CF and non-CF airways toabsorb both ²²Na and³⁶Cl. Two consistent findings wereevident from these studies. First, in both CF and non-CF xenografts,²²Na and³⁶Cl were always absorbed in anequal molar ratio. Second, CF xenografts hyperabsorbed (~1.5-foldhigher) both ²²Na and³⁶Cl compared with non-CFxenografts. These results substantiate previously documented findingsof elevated Na absorption in CF airways and also suggest that theslightly elevated[Cl]_s found in thisstudy of CF xenograft epithelia does not occur through a mechanism ofdecreased apical permeability to Cl.     

Isoosmotic regulation of cotton and peanut at saline concentrations of k and na

Peanut (Arachis hypogaea L.) and cotton (Gossypium hirsutum) plants were grown for 4 weeks in saline, isoosmotic rooting substrates with different proportions of K and Na. Isoosmotic media did not affect growth (except at the highest external K concentrations) or estimates of intracellular osmotic pressure in expanding leaves (i.e. osmotic pressure of leaf sap and intracellular osmotic pressure as calculated from pressure-volume curves). In expanded leaves, an increase in the proportion of external K increased sap osmotic pressure. The sum of [K+Na+Cl] in the sap of expanding and expanded leaves accounted for the effect of isoosmotic media on the concentration of osmolytes with high electrical conductance, so the difference between sap osmotic pressure and [K+Na+Cl] accounted for the concetration of osmolytes with low conductance. In expanding leaves, an increase in the proportion of external K increased [K+Na+Cl] and decreased the concentration of osmolytes with low conductance. In expanded leaves, an increase in the proportion of external K increased [K+Na+Cl] to approximately the same extent as sap osmotic pressure. Isoosmotic regulation was apparent in expanding leaves but not evident in expanded leaves. This suggests a turgor homeostat which can influence the concentration of organic solutes in expanding leaves but cannot control the import of inorganic solutes from a rooting medium nor the total production of organic solutes in plants with a low sink:source ratio.     

The Control of Na Uptake into Nitella translucens

Movement of Na into cells of Nitella translucens is a ‘downhill’process; the ions move across the plasmalemma down an electrochemicalpotential gradient. Nevertheless, measurements of Na influxesunder a wide range of experimental conditions have shown thatthere must be links between Na uptake and processes controlledby metabolism. When Ca ions are present in the bathing solution,Na influxes are greatly increased by light under conditionswhere photosynthesis can proceed (i.e. when both photosystemsare active). In the presence of Ca, the influx of Na increasesonly slightly when the external Na concentration is raised above1 mM, and the light-promoted Na influx is considerably inhibitedwhen Cl is removed from the bathing solution. When the Cl concentrationis kept constant, the Na influx in light is determined by theconcentrations of other cations present in solution (K, Ca,or NH₄). In the absence of Ca from the cell wall and solution,the influx is stil enhanced by light, but does not saturatewhen the external Na concentration is raised above 1 mM. Itis suggested that the Na influx in light is partly linked tothe inward Cl pump, but there is also a separate (Cl-independent)effect of light on the permeability of the plasmalemma to Na.Links between Na and Cl uptake could be maintained by effectsof Cl on electrochemical driving forces controlling Na entry;alternatively, chemical coupling between the two processes maybe involved.     

IONIC COMPOSITION OF THE CYTOPLASM OF NITELLA FLEXILIS

The K, Na and Cl concentrations of the chloroplast layer andthe flowing cytoplasm of Nitella flexilis have been determinedby applying an internal perfusion technique, which enabled usto avoid contamination of ions from the cell sap. K, Na andCl concentrations of the chloroplast layer are 110, 26 and 136mM and those of the flowing cytoplasm are 125, 5 and 36 mM respectively.The cell sap contains 80 mM K, 28 mM Na and 136 mM Cl. Althoughthere are some variations in these values among samples, theflowing cytoplasm is rich in K and poor in Cl and especiallyin Na. The exchange of K and Na across the tonoplasl occursfairly easily (half-time, a few hours), while that of Cl occursextremely slowly (half-time, a few days). ¹This work was supported by Research Grants from the Ministryof Education of Japan     

Chemical Composition of Bleeding Xylem Sap from Kiwifruit Vines

A study of the chemical composition and charge balance was madeof bleeding xylem sap collected from excised one-year-old extensionshoots of healthy, Mn-deficient, Mn-toxic and Zn-deficient kiwifruitvines (Actinidia deliciosa (A. Chev.) C. F. Liang et A. R. Ferguson)immediately prior to leafburst. The exudates were analysed formacronutrient cations and anions, trace elements, amino acids,organic acids and sugars. Major charged species measured wereCa (13.3 mM), K (8.9 mM), Mg (5.6 mM), malate (12.5 mM) andphosphate (5.8 mM). Glutamine (12 mM) was the predominant Ncarrier identified, accounting for 58 per cent of the totalN followed by NO₂^–-N (4.5 per cent), NH₄⁺-N (3.5 per cent)and arginine-N (2.9 per cent). Approximately 22 per cent ofthe N was in a hydrolysable proteinaceous fraction comprisingmainly glutamine and glutamate. Eighteen free proteinaceousamino acids were idetified in sap, the most abundant being glutamine,glutamic acid, valine, isoleucine and phenylalanine. Computersimulation of the chemical composition predicted that in additionto hydrated cations, ion pairs formed between inorganic components(SO₄^2–, HPO₄^2–, H₂PO₄^–) and cations (Ca²⁺,Mg²⁺, Mn²⁺), plus metal-organic ligand complexes (Ca Malate,Zn Malate, FeCit, CuHis, CuGln) are important species involvedin translocation. The solubility product of hydroxyapatite wasexceeded in all exudates although in vitro precipitation wasnot observed. To achieve electroneutrality with the componentsmeasured, however, formation of precipitate precursors (hydroxyapatitenuclei) had to be assumed. Irregularities in Mn nutrition (butnot Zn) were clearly indicated by the elemental compositionof exudate suggesting the use of sap analysis as a possiblepre-season indicator of nutritional status for this species. Actinidia deliciosa (A. Chev.) C. F. Liang et A. R. Ferguson, kiwifruit, xylem sap composition, trace metals, amino acids, organic acids     

Transfer Cells in Roots of Phaseolus coccineus: Ultrastructure and Possible Function in Exclusion of Sodium from the Shoot

A study was made of ultrastructural aspects and ion distributionin roots of Phaseolus coccineus as affected by NaCl and Na₂SO₄salinity. In the proximal region of the root, xylem parenchymacells are differentiated as transfer cells with well developedwall protuberances adjacent to the half-bordered pits of thevessels. The cytoplasm of these transfer cells contains cisternaeof rough endoplasmic reticulum, the number of which was increasedgreatly when the plants were grown in the presence of NaCl orNa₂SO₄. The cisternae of the endoplasmic reticulum are oftenassociated closely with the plasmalemma and interconnected withit by fibrillar bridges. Wall protuberances occur also in the exodermis and epidermisof the more apical region of the root. Their function is stillunknown. P. coccineus excludes Na, but not Cl, from the leaves by retainingit particularly in the proximal region of the root. X-ray microanalysisof unfixed, frozen, hydrated specimens revealed that the transfercell-type xylem parenchyma cells in salt-treated roots accumulatedNa relative to both the adjoining xylem vessels and the corticalcells and showed very high Na/K and Na/Cl ratios. It is suggestedthat the xylem parenchyma cells can reabsorb Na from the vessels,probably in exchange for K, and that Na exclusion from the shootis at least partly mediated by this process. The implicationof this for regulation of salt transport in salt sensitive glycophytesis discussed.     

Mobilization of Minerals to Developing Seeds of Legumes

The mineral nutrition of fruiting plants of Pisum sativum L.,Lupinus albus L. and Lupinus angustifolius L. is examined insand cultures supplying adequate and balanced amounts of essentialnutrients. Changes in content of specific minerals in leaves,pods, seed coat, and embryo are described. P, N and Zn tendto increase precociously in an organ relative to dry matteraccumulation, other elements more or less parallel with (K,Mn, Cu, Mg and Fe) or significantly behind (Ca and Na) dry weightincrease. Some 60–90 per cent of the N, P and K is lostfrom the leaf, pod and seed coat during senescence, versus 20–60per cent of the Mg, Zn, Mn, Fe and Cu and less than 20 per centof the Na and Ca. Mobilization returns from pods are estimatedto provide 4–39 per cent of the seeds' accumulations ofspecific minerals, compared with 4–27 per cent for testatransfer to the embryo. Endosperm minerals are of only minorsignificance in embryo nutrition. Comparisons of the mineral balance of plant parts of Lupinusspp. with that of stem xylem sap and fruit tip phloem sap supportthe view that leaves and pod are principal recipients of xylem-borneminerals and that export from these organs via phloem is themajor source of minerals to the seeds. Endosperm and embryodiffer substantially in mineral compostition from phloem sap,suggesting that selective uptake occurs from the translocationstream during seed development. Considerable differences are observed between species in mineralcomposition of plant organs and in the effectiveness of transferof specific minerals to the seeds Differences between speciesrelate principally to Ca, Na and certain trace elements.     

Variations in the Mineral Composition of Herbarium Plant Species Collected During the Last Three Centuries

Mineral content (dry weight basis) was determined for herbariumspecimens of 12 C₃ plants (trees, shrubs and herbs) collectedduring the last 250 years in N.E. Spain. Present values of Al,Ca, Cu, Sr, Fe, P, Mg, Mn, K, Na, S, and Zn were always lowerthan in any other period of the last three centuries. Only oneC₄ plant was analysed. It presented a similar pattern to theC₃ plants. These results are in accordance with experimentalresults that have shown that the mineral content of plants grownin elevated CO₂ is generally lowered. Increased atmosphericCO₂ and other anthropogenic environmental changes are suggestedas possible causes of the changes in mineral content. Key words: Leaf mineral content, Al, Ca, Cu, Sr, Fe, P, Mg, Mn, K, Na, S, Zn, herbaria, last three centuries     

ROLE OF CALCIUM IN POTASSIUM UPTAKE BY PLANT ROOTS

The effects of EDTA·Mg or GEDTA·Mg on the uptakeof nutrient ions, the release of Ca⁺⁺ and nucleotides into themedium and the nucleic acid contents in rice and red bean rootswere investigated.

1. Both EDTA and EDTA·Mg induced similarly the release ofCa from roots.
2. EDTA·Mg as well as EDTA brought abouta significant repressionin K uptake, but had an insignificantor no effect on P, NH₄and NO₃ uptakes. EDTA·Ca did notrepress K, P, NH₄ andNO₃ uptakes.
3. EDTA or GEDTA acceleratedthe degradation of nucleic acid andthe release of nucleotides,while EDTA·Mg or GEDTA·Mghad no such effect.

These results indicate that the indispensable role of intracellularCa in K uptake does not appear to be directly associated withRNA metabolism. (Received July 29, 1965; )     

Ammonium Nutrition in Ricinus communis: Its Effect on Plant Growth and the Chemical Composition of the Whole Plant, Xylem and Phloem Saps

Allen, S. and Smith, J A. C. 1986. Ammonium nutrition in Ricinuscommunis: its effect on plantgrowth and the chemical compositionof the whole plant, xylem and phloem saps.—J. exp. Bot.37: 1599–1610. The growth and chemical composition of Ricinus communis cultivatedhydroponically on 12 mol m ^{– 3} NO₃^–-N were comparedwith plants raised on a range of NH₄⁺-N concentrations. At NH₄⁺-Nconcentrations between 0·5 and 4·0 mol m^–3,fresh- and dry-weight yields of 62-d-old plants were not significantlydifferent from those of the NO₃^–-N controls. Growth wasreduced at 0·2 mol m^–3 NH₄⁺-N and was associatedwith increased root. shoot and C: organic N ratios, suggestingthat the plants were N-limited. At 8·0 mol m^–3NH₄⁺-N, growth was greatly restricted and the plants exhibitedsymptoms of severe ‘NH₄⁺ toxicity’. Plants growingon NH₄⁺-N showed marked acidification of the rooting medium,this effect being greatest on media supporting the highest growthrates. Shoot carboxylate content per unit dry weight was lower at mostNH₄⁺-N concentrations than in the NO₃^–-N controls, althoughit increased at the lowest NH₄⁺-N levels. Root carboxylate contentwas comparable on the two N sources, but also increased substantiallyat the lowest NH₄⁺-N levels. N source had little effect on inorganic-cationcontent at the whole-plant level, while NO₃^– and carboxylatewere replaced by Cl as the dominant anion in the NH₄⁺-N plants.This was reflected in the ionic composition of the xylem andleaf-cell saps, the latter containing about 100 mol m^–3Cl^– in plants on 8·0 mol m^–3 NH₄⁺. Xylem-saporganic-N concentration increased more than threefold with NH₄⁺-N(with glutamine being the dominant compound irrespective ofN source) while in leaf-cell sap it increased more than 12-foldon NH₄⁺-N media (with arginine becoming the dominant species).In the phloem, N source had little or no effect on inorganic-cation,sucrose or organic-N concentrations or sap pH, but sap fromNH₄⁺-N plants contained high levels of Cl^– and serine. Collectively, the results suggested that the toxic effects ofhigh NH₄⁺ concentrations were not the result of medium acidification,reduced inorganic-cation or carboxylate levels, or restrictedcarbohydrate availability, as is commonly supposed. Rather,NH₄⁺ toxicity in R. communis is probably the result of changesin protein N turnover and impairment of the photorespiratoryN cycle. Key words: Ricinus, ammonium nutrition, nitrate, whole-plant composition, xylem, Phloem, amino acids, carboxylate