The Geoelectric Effect in Plant Shoots: II. SENSITIVITY OF CONCENTRATION CHAIN ELECTRODES TO REORIENTATION

A concentration chain, static-drop electrode system has beenused by several investigators to measure the geoelectric effectin plant shoots. This paper describes investigations of theinherent sensitivity of this electrode system to reorientationwith respect to gravity. When the gelatine plug of the electrodeis made up with distilled water, and the contact solution is0.1 mM KCl, a potential difference develops immediately afterelectrodes in direct contact are rotated through 90° intothe vertical plane. A similar response is found when the contactsolution is 5 mM CaCl₂. Increasing the concentration of thecontact solution, or incorporating KCl, K₂SO₄, or ZnSO₄ intothe gelatine plug, drastically reduces the potential differencedeveloped after reorientation. The potential difference acrosselectrodes in direct contact decreases as the electrodes age.The potential difference measured with these electrodes acrossa decapitated, horizontally placed, hypocotyl of Helianthusarmuus also decreases as the electrodes age. The polarity ofthe charge is reversed as compared with that found when theelectrodes are in direct contact. The kinetic characteristicsof the geoelectric potential difference developed across a non-decapitated,horizontal coleoptile of Zea mays change as the electrodes age.With fresh electrodes the potential develops immediately afterreorientation and continues to increase with time. With 4-day-oldelectrodes, however, no potential difference develops until9 min after the moment of reorientation, but then it increaseswith time. The characteristics of the geoelectric potentialdifference developed with the aged concentration-chain, static-dropelectrodes are similar to those found with several other typesof electrodes which do not themselves have an inherent sensitivityto reorientation with respect to gravity. The results supportour earlier suggestion that the potential difference which apparentlydevelops with the static-drop electrode system, immediatelyafter a shoot is turned through 90° in reality developsin the electrode system itself and not in the plant tissue.The geoelectric effect which arises in the living plant shootbegins to develop approximately 10 min after reorientation.     

Regulation of Free Calcium Concentration in the Pitchers of the Carnivorous Plant Sarracenia purpurea: A Model for Calcium in the Higher Plant Apoplast?

The pitcher of the carnivorous plant Sarracenia purpurea L.contains an entrapped body of liquid within which its prey isdigested. Free calcium in the pitcher is derived from eitherthe pitcher walls or from prey falling into the pitcher; inthe absence of exogenous (prey-derived) calcium it will dependon the active and passive calcium regulatory properties of thepitcher walls and may to some extent therefore mimic calciumin the apoplast of plant cells. Using a calcium-specific electrode,the free calcium concentration of the pitchers of Sarraceniaplants was investigated and the effect of adding a variety ofconcentrations of calcium in water determined. The mean pitcherfree calcium concentration in vivo was 2.3 x 10^–5 M±2.5x 10^–5 M; when pitchers were washed and filled with watercontaining lower calcium concentrations, the concentration inthe pitcher water rose to 1–5 x 10^–5 M. When highercalcium concentrations (up to 1 x 10^–4 M) were added,the pitcher calcium concentration declined to 1–7 x 10^–5M. Concentrations of calcium above 1 x 10^–4 M were alsoreduced, but to a lesser extent. Metabolic inhibition of activeion transport, while inhibiting pitcher acidification, did notinhibit regulation of pitcher free calcium, suggested that itoccurs as a result of calcium exchange sites in the pitcherwalls. The data are discussed in relation to the physiologyof Sarracenia pitchers and to the usefulness of the pitcheras a model for free calcium in the higher plant apoplast. Sarracenia purpurea L., carnivorous plant, pitcher, free calcium, plant apoplast     

Cyclic Nucleotides and In Vitro Plant Cultures: I. INDUCTION OF ORGANOGENESIS IN TOBACCO (NICOTIANA TABACUM CALLUS CULTURES

Mangat, B. S. and Janjua, S. 1987. Cyclic nucleotides and invitro plant cultures. I. Induction of organogenesis in tobacco(Nicotiana tabacum) callus cultures.—J. exp. Bot. 38:2059–2067. The possibility that cyclic nucleotides have a mediatory rolesimilar to cytokinins in plant tissue cultures was examined.Calli obtained from tobacco pith tissue were incubated on growthmedia supplemented with either cyclic AMP, cyclic GMP, adenosineor guanosine, in concentrations ranging from (mg dm^–3)0 to 2·0 together with 2·0 mg dm^–3 of IAA.Results were compared with identical calli grown on media containingcomparable amounts of kinetin and IAA. Increase in callus growthwas observed on all media containing cyclic AMP, cyclic GMP,adenosine, guanosine or kinetin. Adenosine or guanosine didnot promote organogenesis. Low concentrations (0·02 and0·05 mg dm^–3) of kinetin stimulated extensive rootdevelopment. Some root formation was also elicited with higheramounts of cyclic AMP (0·1 and 0·2 mg dm^–3)or cyclic GMP (0·2 and 0·5 mg dm^–3). Bothkinetin and cyclic GMP promoted shoot differentiation. However,in contrast to kinetin, cyclic GMP induced organogenesis atlower concentrations (0·02 and 0·1 mg dm^–3).The addition of 2·0 mg dm ^–3 of cyclic AM P toIAA-free growth media elicited shoot differentiation. This wasalso the case with a similar concentration of kinetin or cyclicGMP. Results suggest cytokinin activity for the two cyclic nucleotides. Key words: Tobacco, Nicotiana tabacum, tissue culture, cyclic nucleotides, cyclic AMP, cyclic GMP organogenesis     

Making heads from tails: Development of a reversed anterior-posterior axis during budding in an acoel

The anterior-posterior axis is a key feature of the bilaterian body plan. Although axis specification during embryogenesis has been studied extensively, virtually nothing is known about how this axis can be established post-embryonically, as occurs in budding animals. We investigated bud formation in the acoel Convolutriloba retrogemma, which reproduces by a remarkable process involving the formation of animals with linked but completely opposite body axes. Reverse axes are established anew during each round of budding and manifestations of the bud's new axis develop gradually, with regionalization of axial patterning genes (Hox and otx) and the establishment of organized musculature occurring secondarily, after bud initiation. A swath of tissue at the parent-bud boundary has no regenerative potential and appears devoid of inherent axial polarity. GSK-3 inhibitor trials suggest that Wnt/β-catenin or Hedgehog signalling may mediate the establishment of this unpolarized zone. Formation of unpolarized tissue may provide a buffer between opposing polarity cues and be a general mechanism by which budding animals establish and maintain linked body axes. In addition to elucidating the developmental basis of budding in a bilaterian, this study provides insight into convergence in animal budding mechanisms, redeployment of embryonic gene expression during budding, and Hox gene evolution.     

Energetic basis of the light-induced chloroplast shrinkage in vivo

A light-induced chloroplast shrinkage occurring in vivo wasmeasured with a Coulter counter and a packed weight techniqueusing chloroplasts isolated within two minutes of harvestingpea plants. Introduction of the photosynthetic inhibitor DCMU(5 µM) into the plant either by bathing the cut stem orinjection through a fine hypodermic needle decreased the light-inducedchloroplast shrinkage in vivo 11 to 20%. The uncoupler tri-Fl-CCP(5 µM) inhibited the light-induced shrinkage 80 % , whilenigericin (0.5 µM) completely abolished it. An actionspectrum for the chloroplast volume decrease in vivo had a shoulderat 700-715 mµ. These results are considered in terms ofthe various forms of energy available during photosynthesis.A consistent interpretation is that the lightinduced chloroplastshrinkage in vivo depends either on a high energy state createdby electron flow or on ATP. This chloroplast volume change uponillumination of the plants may increase the photosynthetic efficiency. (Received April 15, 1968; )     

Relationship Between the Development and Growth of Rye (Secale cereale L.) and the Potassium Concentration in Solution

The development and growth of rye (Secale cereale L. cv. Rheidol)was studied in seedlings grown hydroponically in complete nutrientsolutions containing between 10 and 600 µM K⁺. The phyllochron(defined as the interval between the appearance of successiveleaves) was used as a developmental timescale to compare plants.The pattern of both shoot and root development was strictlyordered on a phyllochron basis and was unaffected by solutionK⁺ concentration, with the exception that tillers in plantsgrown at the lowest K⁺ concentrations were occasionally eithernot initiated or aborted at an early stage of development. However,both the rate of leaf appearance on the main stem and successivetillers and the rate of tiller appearance were slower in plantsgrown at lower K⁺ concentrations. The rate of leaf appearanceon the main stem was reduced to below 90% of its maximal valueat solution concentrations below about 50 µM K⁺. Plantrelative growth rate (RGR) was also reduced by lowering theK⁺ concentration of the nutrient solution and fell to below90% of its maximal value at solution concentrations below about200 µM K⁺. There was a complex relationship between tissueK⁺ concentration and the K⁺ concentration of the nutrient solution,which differed between leaves and root. Leaf K⁺ concentrationincreased steadily from about 50 µmol g^-1 f. wt to about200 µmol g^-1 f. wt as solution K⁺ concentration was increasedfrom 10 to 400 µM. In contrast, root K⁺ concentrationexhibited a sigmoidal dependence on solution K⁺ concentration,maintaining a minimal value of approximately 20 µmol g^-1f. wt at concentration below 100 µM K⁺, then increasingprogressively to about 120 µmol g^-1 f. wt at a solutionconcentration of 600 µM K⁺. The 'critical' leaf K⁺ concentration,i.e. the concentration at which either plant RGR or plant developmentwas reduced 90% of its maximal value, was 86 µmol g^-1f. wt for plant RGR and 150 µmol g^-1 f. wt for plant development.The 'critical' root K⁺ concentration was 24 µmol g^-1 f.wt K⁺ for both RGR and development. A decline in tissue K⁺ concentrationbelow these thresholds reduced plant growth considerably. RootK⁺ concentration was a sensitive indicator of the K⁺ statusof the plant with respect to potential growth since plant growthdeclined abruptly as root K⁺ concentration approached its 'critical'value, whereas plant growth showed a less defined relationshipwith shoot K⁺ concentration.Copyright 1993, 1999 Academic Press Critical K⁺ concentration, development, potassium, relative growth rate (RGR), rye, Secale cereale L. cv. Rheidol     

The Uptake and Utilization of Phosphorus and Nitrogen by Diploid, Tetraploid and Hexaploid Wheats (Triticum spp.)

Twenty genotypes of Triticum and Aegilops wheats including diploid,tetraploid and hexaploid types, were grown under contrastingphosphorus (P) regimes (control and low P) at 15 °C by dayand 10 °C at night. Dry-matter production and phosphorusand nitrogen uptake and distribution were measured on matureplants. Phosphorus efficiency (PE) was considered in terms of yieldper unit of P in the main shoot and concentration of phosphorusin grain (per cent P). In the low-P set, PE, which ranged from110 to 715 mg grain mg^–1 P, increased as the yield perculm and dry-matter partitioning (harvest index) increased,with hexaploid > tetraploid > diploid. In both the controland low-P plants percentage P in grain decreased in the orderdiploids > tetraploids > hexaploid wheats. Grain phosphoruswas highly negatively correlated with the log of grain yield(r = –0.74; –0.88) and the log of harvest index(r = –0.80 and –0.88) for control and low-P plants,respectively. This suggests that future gains in plant harvestindex will cause smaller reductions in grain phosphorus concentrations.But, within either a high or low phosphorus supply, wheats witha given grain harvest index have significantly different grainphosphorus concentrations, and conscious selection for thischaracter is feasible. Low-P plants had similar grain nitrogen concentrations but lowernitrogen harvest indexes than control plants. Aegilops spp., Triticum spp., wheat, yield components, harvest index, polyploidy, evolution, phosphorus efficiency     

Seasonal Water Acquisition and Redistribution in the Australian Woody Phreatophyte, Banksia prionotes

Sap flows in the xylem of plant roots in response to gradientsin water potential, either between soil and atmosphere (transpiration)or soil layers of different moisture content (termed hydraulicredistribution). The latter has the potential to influence waterbudgets and species interactions, but we lack information forall but a few plant communities. We combined heat pulse measurementsof sap flow with dye and isotope tracing techniques to gaugethe movement of xylem sap within, and exudation from, rootsof Banksia prionotes (Lindley). We demonstrated ‘ hydrauliclift’ during the dry season and provide some evidencethat extremely dry soils limit hydraulic lift. In addition wereport difficulties posed by spiralled xylem tissue in rootsfor the application of heat pulse techniques. Copyright 2000Annals of Botany Company Banksia prionotes, sap flow, hydraulic lift, heat ratio method, deuterium, stable isotopes, root architecture.     

Pea Root Regeneration After Tip Excisions at Different Levels: Polarity of New Growth

The roots of light-grown pea seedlings (Pisum sativum L. cv.Alaska) were excised at 250, 500 or 1500 µm from the body/capjuncture. Tips were sampled for 7 d after excision to monitorthe polarity and structure of the regeneration response. Inroots excised at 250 µm a new single apex regeneratedwithout swelling or any sign of repair. The new root cap appearedidentical to the control. After the 500 µm excision tworesponses occurred. In 45% of the roots examined, a single newapex regenerated, in 55% two or three new apices regeneratedto form a dichotomized or trichotomized root in the same longitudinalaxis as the primary root. In roots excised at 1500 µm,one, two or three lateral roots formed adjacent to the xylemat right angles to the primary root axis. In most instancesthe new roots developed triarch xylem. The discussion concentrateson the relationship of the differentiation state of the vascularcylinder and the pericycle, at the excision site, to the regenerationresponse. Root regeneration, Pisum sativum, Pericycle, Root apex     

Plant allometry, leaf nitrogen and phosphorus stoichiometry, and interspecific trends in annual growth rates

• Background Life forms as diverse as unicellular algae,zooplankton, vascular plants, and mammals appear to obey quarter-powerscaling rules. Among the most famous of these rules is Kleiber's(i.e. basal metabolic rates scale as the three-quarters powerof body mass), which has a botanical analogue (i.e. annual plantgrowth rates scale as the three-quarters power of total bodymass). Numerous theories have tried to explain why these rulesexist, but each has been heavily criticized either on conceptualor empirical grounds. • N,P-Stoichiometry Recent models predicting growth rateson the basis of how total cell, tissue, or organism nitrogenand phosphorus are allocated, respectively, to protein and rRNAcontents may provide the answer, particularly in light of theobservation that annual plant growth rates scale linearly withrespect to standing leaf mass and that total leaf mass scalesisometrically with respect to nitrogen but as the three-quarterspower of leaf phosphorus. For example, when these relationshipsare juxtaposed with other allometric trends, a simple N,P-stoichiometricmodel successfully predicts the relative growth rates of 131diverse C₃ and C₄ species. • Conclusions The melding of allometric and N,P-stoichiometrictheoretical insights provides a robust modelling approach thatconceptually links the subcellular ‘machinery’ ofprotein/ribosomal metabolism to observed growth rates of uni-and multicellular organisms. Because the operation of this ‘machinery’is basic to the biology of all life forms, its allometry mayprovide a mechanistic explanation for the apparent ubiquityof quarter-power scaling rules.     

Rapid Shoot Propagation from Micro-Cross Sections of Kiwifruit (<Emphasis Type="Italic">Actinidia deliciosa</Emphasis> cv. ‘Hayward’)

Kiwifruit shoots can be rapidly propagated through a micro-cross section (MCS) system we established here. Optimal culture conditions were determined for different expiant types, section sizes, and concentrations of inorganic salts and plant growth regulators. Rates of survival and callus formation were higher in half-strength MS salts than in full-strength MS media. Similar performance (i.e., survival and callus formation) was achieved with section sizes of either 800 μm or 1200 μm. Proliferation efficiency was greatest when expiants from stem tissue were cultured on 1/2 MS supplemented with 4.5x10^-3 μM 2,4-dichlo-rophenoxyacetic acid and 4.6x10^-1 μM zeatin. The number of shoots averaged 2.61 per expiant, representing an efficiency of 94%. RAPD analysis revealed that the regenerated plants from our MCS system were genetically stable. These results show that the culturing of micro-cross sections from stem tissue is a powerful method for kiwifruit propagation.     

Leaf Growth in Cotton (Gossypium hirsutum L.) 1. Growth in Area of Main-stem and Sympodial Leaves

A model is presented for growth of individual and successivemain-stem leaves of cotton, based on a series of indoor experimentsand data sets from the literature. Three variable parametersare used to describe individual leaf growth: relative growthrate of meristematic tissue (R¹), relative rate of approachof final area (R₂) and a ‘position parameter’ (t_0.5)which governs the transition from meristematic to extensiongrowth. Final area of a leaf does not occur in the model asa deterministic quantity but it is a result of the processesduring growth. The model generates successive mainstem leavesand sympodial leaves as an integrated system. Assimilate shortagesoccurring in the plant operate on R₁ leading to the characteristicchange of final leaf area along the mainstem. Gossypium hirsutumL., cotton, leaf growth, relative growth rate, meristematic tissue, extension growth, mathematical model     

Effects of elevated carbon dioxide on three montane grass species: I. Growth and dry matter partitioning

Upland grasslands are a major component of natural vegetationwithin the UK. Such grasslands support slow growing relativelystable plant communities. The response of native montane grassspecies to elevated atmospheric carbon dioxide concentrationshas received little attention to date. Of such studies, mosthave only focused on short-term (days to weeks) responses, oftenunder favourable controlled environment conditions. In thisstudy Agrostis caplllaris L.⁵, Festuca vivipara L. and Poa alpinaL. were grown under semi-natural conditions in outdoor open-topchambers at either ambient (340µmol mol^–1) or elevated(680µmol mol^–1) concentrations of atmospheric carbondioxide (CO₂ for periods from 79 to 189 d, with a nutrient availabilitysimilar to that of montane Agrostis-Fescue grassland in Snowdonia,N. Wales. Whole plant dry weight was increased for A. capillarisand P. alpina, but decreased for F. vivipara, at elevated CO₂.Major components of relative growth rate (RGR) contributingto this change at elevated CO₂ were transient changes in specificleaf area (SLA) and leaf area ratio (LAR). Despite changes ingrowth rate at 680 µmol mol^–1 CO₂, partitioningof dry weight between shoot and root in plants of A. capillarisand P. alpina was unaltered. There was a significant decreasein shoot relative to root growth at elevated CO₂ in F. viviparawhich also showed marked discoloration of the leaves and increasedsenescence of the foliage. Key words: Allometry, growth analysis, elevated CO₂, grasses     

Influence of Endophyte and Water Regime Upon Tall Fescue Accessions. II. Pyrrolizidine and Ergopeptine Alkaloids

Alkaloids, along with specific environmental conditions, havebeen associated with both detrimental and beneficial aspectsof endophyte (Acremonium coenophialum Morgan-Jones et Gams)infected tall fescue (Festuca arundinacea Schreb.) associations.Benefits to the plant accrue through reduced herbivory, whereasdetriment to the animal occurs as altered grazing behaviourand reduced productivity. A controlled environment study wasconducted to examine pyrrolizidine and ergopeptine alkaloidconcentration of four tall fescue accessions as influenced byendophyte status and water regime. Endophyte-free plants weredevoid of ergopeptine alkaloid and contained little, if any,pyrrolizidine alkaloid. Leaf blade tissue of endophyte-infectedisolines contained a range of both ergopeptine (256 to 1633ng g^–1) and pyrrolizidine (92 to 450 µg g^–1)alkaloid concentrations. Water deficit generally increased alkaloidconcentration. Alkaloid yield, based upon concentration andtissue d. wt, showed that significant increase in ergopeptineand pyrrolizidine alkaloid in leaf tissue was associated withwater deficit and was due to actual increased synthesis andnot simply decreased phytomass. Leaf and pseudostem (leaf sheathand stem base) tissue alkaloid concentrations indicated differentaccumulation patterns for ergopeptine and pyrrolizidine alkaloids.Ergopeptine alkaloid yield increased in water-stressed pseudostem,whereas pyrrolizidine alkaloid yield decreased in some, butnot all accessions. The range of host genotype/endophyte biotyperesponse offers the possibility to select associations whichproduce few deleterious effects in animals yet maintain highforage productivity and persistence. Festuca arundinacea, Acremonium coenophialum, tall fescue genotypes, water stress, N-formyl and N-acetyl loline, ergovaline     

Effects of photon flux density on carbon partitioning and rhizosphere carbon flow of Lolium perenne

The distribution and partitioning of dry matter and photoassimilateof Lolium perenne was investigated under two light regimes providingphotosynthetically active radiation of 350 µmol m^–2s^–1 (low light treatment) or 1000 µmol m^–2s^–1 (high light treatment). Plants were grown at specificgrowth conditions in either soil or sand microcosm units tofollow the subsequent release of carbon into the rhizosphereand its consequent incorporation into the microbial biomass(soil system) or recovery as exudates (sand system). The distributionof recent assimilate between the plant and root released carbonpools was determined using ¹⁴CO₂ pulse-chase methodology atboth light treatments and for both sand- and soil-grown seedlings.A significant (P     

The Uptake of Phosphate by Plants from Flowing Nutrient Solution: I. CONTROL OF PHOSPHATE CONCENTRATION IN SOLUTION

An existing system of flowing solution culture in which pH andthe concentration of several nutrient ions in solution are automaticallymonitored and controlled has been extended to include the monitoringand control of orthophosphate in the range 0.0013 to 0.3 mgP l^–1 (4.2 ? 10^–8–10^–5 M). Continuous-flowcolorimetry is used for the analysis of phosphate and a computeris employed to hold concentrations constant by the operationof nutrient pumps. A brief account is given of the performanceof the system with perennial ryegrass (Lolium perenne L.) asthe experimental plant.     

On the trophic fate of Phaeocystis pouchetii (Harlot). III. Functional responses in grazing demonstrated on juvenile stages of Calanus finmarchicus (Copepoda) fed diatoms and Phaeocystis

The objective of this study was to quantify the functional responsein feeding rate in the various developmental stages of Calanusfinmarchicus to different concentrations of the diatoms Thalassiosiranordenskioeldii and Porosira glacialis, and the haptophyseanPhaeocystis pouchetii. Grazing of copepodite stage I–VC.finmarchicus was measured using two different approaches.Feeding rates were obtained from either incubation experiments,estimating the rate of removal of particles from suspension,or by quantifying the turnover rate of the plant pigments inthe gut. Clearance as a function of algal concentration (1–30µg plant pigment 1^–1) was described in juvenilestages of C.finmarchicus fed the diatoms T.nordenskioeldii [20µm equivalent spherical diameter (ESD)], P.glacialis (40µm ESD), and two size categories (30–100 µmand >100 µm ESD) of the gelatinous alga P.pouchetii.When the copepodite stages were fed T.nordenskioeldii, the gutcontent of plant pigments was in general higher than when fedP.glacialis. Rates obtained were variable when the same copepoditestages were offered the two size categories of P.pouchetii,but within the same order of magnitude as those obtained forthe larger diatom. At unialgal diets, diatoms were more readilyconsumed than the larger size fraction among colonies of P.pouchetiiby copepodite stage I–III C.finmarchicus. But given anappropriate prey size, C.finmarchicus grazed both diatoms andcolonies of gelatinous algae at equal rates. A linear relationshipbetween gut content and food concentrations <10 µgchlorophyll 1^–1 was found. This indicates that the ingestionrate in C.finmarchicus is directly proportional to the ambientfood concentration during the most productive period in Mayand June in high latitudes irrespective of algal species present. ¹Present address: Marine Biological Laboratory, University ofCopenhagen, Strandpromenaden 5, DK-3000 Helsingør, Denmark ²Present address: Greater Copenhagen Council, Gl. KøgeLandevej 1–3, DK-2550 Valby, Denmark     

Effects of Chloride Salts at High Concentrations on Glycolysis in vitro

KC1, at 200 mM, decreased rates of glycolysis, in vitro, inthe steady state and also increased the time required to reachthe steady state of CO₂ and ethanol formation after glucoseaddition. KCl at 200 mM increased concentrations of fructose-1,6-diphosphateand decreased concentrations of pyruvate, at all times between3 and 120 min after glucose addition. At early times after glucoseaddition, 200 mM KCl decreased concentrations of triose phosphatesand 3-phos-phoglycerate. However, at later times, concentrationsof these two intermediates became higher at 200 mM KC1 thanat low Cl^–; with triose phosphates this occurred for thefirst time at 20 min and with 3-phosphoglyeerate at 60 min afterglucose addition. These and other experiments, including oneusing the crossover theorem of Chance, strongly suggested thatthe increased concentrations of fructose- 1,6-diphosphate andtriose phosphates alleviated severe KCl inhibitions of enzymescatalysing reactions in the conversion of fructose-l,6-diphosphateto 1,3-diphosphoglycerate. Similar phenomena occurred for otherparts of the pathway. Thus, the glycolytic sequence respondedto high KCl and NaCl concentrations in a manner predicted fromearlier published experiments with single enzymes, in whichKCl and NaCl inhibitions were much smaller at high than at lowsubstrate concentrations. For the steady state, addition of purified enzymes showed thathigh KCl reduced glycolysis, at least partly by persistent inhibitionsof glyceraldehyde-3-phosphate dehydrogenase and/or aldolase. Overall, the data suggest that high KCl and NaCl concentrationshave two main effects: (1) a transient reduction in rate ofglycolysis—this effect disappears when substrates of certainenzymes have increased above the initial low levels; and (2)inhibitions which persist despite high intermediate concentrations,i.e. inhibitions which occur even in the ‘steady state’.The relevance of these in vitro data to in vivo responses athigh salt concentrations is briefly discussed.     

Aluminium and the Hydraulic Conductivity of Quercus rubra L. Root Systems

Two hydroponic experiments were conducted to determine the effectsof brief and prolonged AI³⁺ exposures on the hydraulic conductivity(Lp) of northern red oak (Quercus rubra L.) root systems. RootLp was determined using the pressure chamber method of Fiscus(1977). In the first experiment, 28- to 40-d-old seedlings weretreated for 4 d with complete nutrient solutions containingone of three Al concentrations (0.04, 1.85 or 3.71 mol m^–3)and either 0 or 50 mmol m^–3 P. Neither Lp nor daily transpirationwas affected by treatment. In Experiment II, seedlings were grown for 48–63 d incomplete solutions containing one of three Al concentrations(0, 0.75 or 2.00 mol m^–3) and either 10 or 250 mmol m^–3Ca. Lp and leaf area to root length ratio (LA/RL) were reducedwhen (AI³⁺/ Ca²⁺), the solution activity ratio, was 2.9 andhigher. Lp and LA/RL were also negatively correlated with Alconcentration and Al/Ca concentration ratio in the roots. Lpwas positively correlated with LA/RL in both experiments. Itis unclear whether Lp in the second experiment was reduced directlyby solution and root chemistry or whether Lp changed in responseto altered leaf/root balance. Key words: Al phytotoxicity, Al x Ca interaction, Quercus rubra, root hydraulic conductivity     

The Effect of Morphactin on the Kinetics of Indol-3yl-acetic Acid-2-14C Transport in Zea mays L. Coleoptile Segments

This paper elucidates the effects of chloroflurenol (morphactin,IT 3456) treatment on the kinetics of ¹⁴C-IAA transport throughZea mays L. (cv. Orla-266) coleoptile segments. Maximum inhibitionof transport was achieved when chloroflurenol remained in contactwith the tissue segments for at least 20 min or more. The treatment,without materially affecting the ¹⁴C-IAA-transport polarity,or uptake, significantly reduced the velocity from 20.5 mm h^–1to 8.79 mm h^–1 and also the intensity from 919 (ct/min)h^–1 to 413 (ct/min) h^–1.