Comparison of the Respiratory Metabolism of Plantago lanceolata L. and Plantago major L.

Bryce, J. H. and ap Rees, T. 1985. Comparison of the respiratorymetabolism of Plantago lanceolata L. and Plantago major L.—J.exp. Bot. 36 1559–1565. The aim of this work was to discover if the respiratory metabolismof the roots of Plantago lanceolata L. differed from that ofthe roots of Plantago major L. Measurements of oxygen uptakeand dry weight of excised root systems during growth of seedlingsprovided evidence that the two species differed in the amountof respiration needed to support a given increase in dry weight.Excised root systems were given a 6-h pulse in [U-¹⁴C]sucrosefollowed by a 16.5-h chase in sucrose. The detailed distributionof ¹⁴C amongst the major components of the roots at the endof the pulse and the chase revealed no significant differencebetween the two species. Patterns of ¹⁴CO₂ production from [1-¹⁴C],[2-¹⁴C], [3,4-¹⁴C], and [6-¹⁴C]glucose of excised root systemsfrom plants of three ages were similar for the two species.It is suggested that there is no conclusive evidence for anysignificant inherent difference in the respiratory metabolismof the roots of the two species. Key words: ¹⁴C sugar metabolism, respiration, roots, Plantago     

Total Uptake and Incorporation into DNA of 3H-Thymidine, 3H-Deoxyuridine, and 3H-Thymine in the Primary Root of Vicia faba L.: II. EXCISED ROOTS

Total uptake of ³H-thymidine, ³H-thymine, and ³H-deoxyuridineand incorporation of these substances into DNA have been investigatedin excised roots in Vicia faba. Total uptake was found to behigher in excised roots than in intact ones. This was a consequenceof exogenous ³H-DNA precursors entering the excised roots throughthe cut surface. Where the cut surface was not immersed in the³H-thymidine solution ³H uptake was also higher than in intactroots. In this case ³H uptake scemed to be correlated with water-lossfrom the cut surface. Incorporation of ³H-thymidine, ³H-thymine,and ³H-deoxyuridine into DNA was found to be higher in excisedroots than in intact ones, probably as a result of a decreasein the size of the relevant endogenous precursor pools. It issuggested that this decrease resulted from the cessation ofthe supply of DNA precursors to these roots from the cotyledons.     

The Relationship between the Cell Electrical Potential Difference and Salt Uptake in the Roots of Helianthus annuus

The effect of ringing the stem on the electrical potential difference(PD) in the root cortical cells of H. annuus was studied. PDand salt transport were followed simultaneously. By ringingit was possible to separate the PD from K⁺, , and Cl^– uptake and H⁺ efflux. The uptake of phosphatehowever was found to be closely connected with a component ofthe PD. It was concluded that there is an electrogenic pumpfor phosphate in these roots which generates 60–80 mV.     

Field Estimates of Root and Xylem Resistances in Pinus contorta using Root Excision

A root excision technique was used to estimate the proportionof total resistance to water flux residing in the soil, theroot, and the xylem of lodgepole pine (Pinus contorta Douglex. Loud.) trees in the field. Root excision at mid-day alwaysresulted in rapid recovery of leaf water potential when waterwas supplied to the cut stem, suggesting a high soil-root resistance.Transpiration was unaffected if leaf water potential beforecutting was not limiting leaf conductance. By mid-June wateruptake by the excised stem always exceeded calculated crowntranspiration indicating recharge of internal sapwood storage.Predawn leaf water potential before root excision was highlycorrelated with total soil-plant resistance (r² = 0·89)and calculated root water uptake (r² = 0·92).     

Sulphate supply and its regulation of transport in roots of a tropical legume Macroptilium atropurpureum cv. Sirato

During a period of sulphate deprivation, roots of Macroptiliumatropurpureum responded by increasing their uptake capacityat the plasma membrane. This effect was apparent both in intactplants and in tissues excised prior to uptake. In experiments using excised root systems previousy labelledwith ³⁵SO₄^2- the rate of tracer transport to the xylem was muchgreater in roots subsequently deprived of external sulphatethan in those supplied with unlabelled sulphate. Removing theexternal sulphate to the external solution. Additionally, compartmentalanalysis of tracer exchange kinetics showed that the flux ofsulphate from the cytoplasm to the xylem(     

Uptake and Physiological Effects of Cadmium in Sugar Beet (Beta vulgaris) Related to Mineral Provision

Sugar beet seedlings (Beta vulgaris L. cv. Monohill) were grownfor 14 d on a nutrient solution based on the nutrient proportionsin healthy plants. Nutrients were supplied either once at relativelyhigh concentrations, or in small amounts with a daily incrementalincrease of 0?15 or 0?20 in accordance with an exponential growthrate. Cadmium (0, 0?6, 2?3, 50 or 20?0 µmol) was introducedeither by a single addition or in daily increments of 0?15 or0?20. Cadmium uptake, expressed as a percentage of total Cd²⁺supplied, decreased with increasing total C^d2+ content and withdecreasing availability of nutrients. With a daily supply ofcadmium, net uptake, transport and content per unit of dry weightin roots and shoots were related to the total Cd²⁺ supplied.Cadmium caused growth retardation, increased root/whole-plantratio, and decreased root-tip respiration and photosynthesis.At high initial nutrient concentrations, Cd²⁺ decreased thecontents of sucrose, glucose, fructose, and starch per unitof dry weight. The opposite was found if nutrients were addeddaily. In the latter case, the dry weight/fresh weight ratioalso increased. The effects of cadmium were related to [Cd²⁺]in proportion both to the root absorption area and to the nutrientconcentration. Key words: Sugar beet, mineral provision, cadmium uptake, sugar formation, growth     

Role of sugars in nitrate utilization by roots of dwarf bean

Nitrate uptake and in vivo, nitrate reductase activity (NRA) in roots of Phaseolus vulgaris, L. cv. Witte Krombek were measured in nitrogen-depleted plants of varying sugar status, Variation in sugar status was achieved at the start of nitrate nutrition by excision, ringing, darkness or administration of sugars to the root medium. The shape of the apparent induction pattern of nitrate uptake was not influenced by the sugar status of the absorbing tissue. When measured after 6 h of nitrate nutrition (0.1 mol m^?3), steady state nitrate uptake and root NRA were in the order intact>dark>ringed>excised. Exogenous sucrose restored NRA in excised roots to the level of intact plants. The nitrate uptake rate of excised roots, however, was not fully restored by sucrose (0.03–300 mol m^?3). When plants were decapitated after an 18 h NO₃^? pretreatment, the net uptake rate declined gradually to become negative after three hours. This decline was slowed down by exogenous fructose, whilst glucose rapidly (sometimes within 5 min) stimulated NG^?₃ uptake. Presumably due to a difference in NO₃^? due to a difference in NO₃^? uptake, the NRA of excised roots was also higher in the presence of glucose than in the presence of fructose after 6 h of nitrate nutrition. The sugar-stimulation of, oxygen consumption as well as the release of ¹⁴CO₂ from freshly absorbed (U-¹⁴C) sugar was the same for glucose and fructose. Therefore, we propose a glucose-specific effect on NO₃^? uptake that is due to the presence of glucose rather than to its utilization in root respiration. A differential glucose-fructose effect on nitrate reductase activity independent of the effect on NO₃^? uptake was not indicated. A constant level of NRA occurred in roots of NO₃^? induced plants. Removal of nutrient nitrate from these plants caused an exponential NRA decay with an approximate half-life of 12 h in intact plants and 5.5 h in excised roots. The latter value was also found in roots that were excised in the presence of nitrate, indicating that the sugar status primarily determines the apparent rate of nitrate reductase decay in excised roots.     

Glucose Induced H+ Influx and Transient Currents in Excised Roots: particularly those of Zea mays

The application of D-glucose to solutions bathing excised maize,wheat, pea and bean roots causes a rapid depolarization of theelectrical potentials between the cut tops of the roots andthe bathing solutions. Similar effects are observed for theplasma membrane potentials of maize lateral roots. A flow cell apparatus was used to demonstrate qualitative andquantitative relations between glucose induced H⁺ influx andthe transient decrease in current through the root. The currentchanges appear to be due entirely to H⁺ fluxes. Current andH⁺ fluxes are strongly influenced by external pH, the optimumpH for glucose induced current change being about 4.0. A similarpH optimum was found for 3-O-methyl-D-glucopyranoside but 1-O-methyl--D-glucopyranosidedid not significantly affect the trans-root potential at anypH, suggesting a significant role for the anomeric hydroxylgroup of glucose. Compounds which depolarize the trans-root potential also inhibitthe glucose induced depolarization. Surface -SH groups are probablynot involved in the glucose/H⁺ cotransport. Eadie-Hofstee plots relating the depolarization of trans-rootpotential to the concentrations of D-glucose or 3-O-methyl-D-glucopyranosidehave shown that K_m values increase with increasing monosaccharideconcentration and are very similar to reported values of 3-O-methyl-D-glucopyranosideuptake in maize root segments. K_m values for a similar rangeof D-glucose concentrations do not vary significantly with pHor with membrane depolarization due to a 10-fold increase ofKCl concentration. However, V_max is lowered by an increase inexternal pH or a decrease in trans-root potential. It appearsthat both proton and electrical gradients can affect glucoseinduced H⁺ influx. The auxin herbicide, 2, 4-dichlorophenoxyethanoic acid (0.01mM) stimulates the glucose induced depolarizations in a mannerconsistent with an increase in cytoplasmic pH. This is discussedin relation to the reported action of indole-3-acetic acid andfusicoccin on maize root tissue.     

A Relationship between Phosphate Uptake and Membrane Electrical Potential in Excised Roots of Helianthus annuus

Phosphate uptake by excised roots of sunflower (Helianthus annuus)was determined by the disappearance of phosphate from the externalsolution and by the accumulation of phosphate labelled with³²P. Over a 24 h period it was observed that net phosphate uptakedeclined to zero whilst uptake of ³²P continued unabated. Theelectrical PD of the cortical cell membranes declined in parallelwith net phosphate uptake and it was found that both could berestored by creating a pH gradient across the plasmalemma. Itwas concluded that net phosphate uptake was responsible fora component of the membrane PD of the root cortical cells. Key words: Roots, Phosphate, Membranes     

Ion Absorption and Allocation of Carbon Resources in Excised Pea Roots Grown in Liquid Medium in Absence or Presence of NaCl

Freshly excised pea roots (Pisum sativum cv. Alaska) when transferredto growth medium (130 mOsm) or growth medium containing salt( 370 mOsm) suffer an initial osmotic shock and lose water.Contol roots tended to accumulate potassium, particularly inthe apical zone, while those exposed to NaCl accumulated mainlysodium, potassium accumulation being depressed. Exposure tosalinity for 6 d caused increases in root protein, cellulose,uronic acid and lignin content per cell. In roots supplied with¹⁴C-glucose for 24 h immediately after excision there was littledifference in uptake of glucose and in its use in respirationbetween control and salt treated roots. However, there werenoticeable differences in incorporation of labelled carbon intoseveral cell fractions, and particularly into the cellulosefraction in the upper parts of the root. When roots were grownfor six days in culture before being supplied with [¹⁴C]glucose,uptake per root was greater in the 120 mM NaCl treatment, andthe fraction diverted to respiration was decreased by salinity.On a per cell basis incorporation into soluble starch, uronicacid and cellulose fractions was increased in the salt treatedroots. The data obtained are in accord with the previous findingsand are suggestive of increased synthesis of cell wall materials.No conclusion could be drawn as to whether the changes describedare of adaptive value. Pisum sativum L. cv. Alaska, root culture, salinity, osmoregulation, cell wall     

Site, Scale and Time-course for Adjustments in Lateral Root Initiation in Wheat Following Changes in C and N Supply

The pattern of lateral root initiation in seminal roots of wheat(Triticum aestivumL. cv. Alexandria) and the location, scaleand time-course for adjustments in initiation were studied afterchanges in C and N supply. Macroscopically visible primordiaappeared in a non-acropetal sequence with the frequency (numberper unit length) increasing with distance behind the main rootapex to a maximum at 40–50 mm behind the root tip. Pruningthe root system to a single seminal axis increased the primordiafrequency by 23% within 15 h. After longer periods, the effectof root-pruning was greater. The enhanced primordia frequencywas first observed in tissue located 0–10 mm behind theapex at the start of treatment. Feeding glucose (50 mM) alsoincreased primordia frequency within 15 h, but to a greaterextent, and here additional primordia were initiated in tissuelocated 0–10and10–20 mm behind the apex at the startof treatment. Withdrawing NO₃^-from one part of a split-rootsystem, whilst maintaining the supply to the other, reducedprimordia frequency in the non-fed roots and, in some cases,a compensatory increase in the NO₃^--fed roots was observed.The location and scale of the adjustments were similar to thosefound with root-pruning and glucose-feeding, but were slightlyslower to appear. In spite of some differences in detail, therewas a broad similarity in site, scale and time-course for adjustmentsin lateral root initiation with these treatments, which is consistentwith the operation of a common mechanism. Whenever an increasein primordia frequency was observed, it was associated withan increase in the ethanol-soluble sugar content of the tissue.However, the reduction in frequency in NO₃^--deprived roots wasalso accompanied by an increase in sugar content. There wasno consistent relationship between total N content of the tissueand primordia frequency, but there was between primordia frequencyand the rate of net NO₃^-uptake. The possible mechanisms controllinglateral root initiation are discussed. Compensatory growth; correlative growth; glucose; initiation; lateral root; nitrate; primordium; split-root; Triticum aestivum; wheat     

Sagebrush (Artemisia tridentata Nutt.) roots maintain nutrient uptake capacity under water stress

Phosphorus and nitrogen uptake capacities were assessed during36–58 d drying cycles to determine whether the abilityof sagebrush (Artemisia tridentata Nutt.) to absorb these nutrientschanged as the roots were subjected to increasing levels ofwater stress. Water was withheld from mature plants in large(6 I) containers and the uptake capacity of excised roots insolution was determined as soil water potentials decreased from–0.03 MPa to –5.0 MPa. Phosphorus uptake rates of excised roots at given substrateconcentrations increased as preharvest soil water potentialsdecreased to –5.0 MPa. V_max and K_m also increased as soilwater potentials declined. Declining soil water potentials depressednitrogen uptake at set substrate concentrations, but uptakecapacity, calculated as the sum V_max for both NH⁺₄+NO^–₃,did not change significantly with drying. The sum V_max correlatedwith root nitrogen concentration. Root uptake capacity for nitrogen and phosphorus was extremelystable under severe water stress in this aridland shrub. Maintenanceof uptake capacity, coupled with a previously demonstrated abilityto conduct hydraulic lift, may enable A. tridentata better tomaintain nitrogen and phosphorus uptake as soil water availabilitydeclines. These mechanisms may be important in the ability ofA. tridentata to maintain growth, complete reproduction, andgain an advantage against competitors late in the season whenthe soil layers with higher nutrient availability are dry. Key words: Kinetics, nitrogen, phosphorus, roots, water stress     

Lateral Root Anlage Development in Excised Roots of Vicia faba L., Pisum sativum L., Zea mays L. and Phaseolus vulgaris L.

The development of lateral root primordia has been investigatedin excised roots of Vicia faba, Pisum sativum, Zea mays andPhaseolus vulgaris cultured in White's medium supplemented with2 per cent sucrose and compared with previously published dataon such development in primaries of the corresponding intactplants (control roots). Primordia were produced in each batchof excised roots over the 6 day culture period but at a lowerrate (number day^–1) than in the controls. Such primordia in cultured roots of Zea and Phaseolus completedtheir development and grew out as lateral roots over a periodsimilar in length to that found in the controls, but with acell number of only about 33 per cent of that attained at thetime of secondary emergence in the primaries of the latter roots.These lower cell numbers were at least partly a reflection ofincreases in mean cell doubling time over the period of anlagedevelopment investigated in the excised roots relative to thecorresponding values found in the controls. Primordia initiated in excised roots of Pisum and Vicia didnot complete their development in culture, i.e. no lateral rootsemerged and arrest took place with cell numbers of only 37 (Pisum)and 17 (Vicia) per cent of the numbers determined at the timeof secondary root emergence in the controls. Such arrested primordiahad few nuclei in S and none in mitosis. Moreover, at leastin Pisum, the frequency distribution of the relative DNA contentof the nuclei in the latter primordia approximated that foundin the apical meristem of primary roots following the establishmentof the stationary phase under conditions of carbohydrate starvation. It has also been demonstrated in the course of these investigationsthat lateral root primordium development in all four speciesis at least biphasic and possibly triphasic. Vicia faba L., broad bean, Pisum sativum L., garden pea, Zea mays L., maize, Phaseolus vulgaris L., dwarf bean, root primordia, anlage, cell doubling time, lateral root emergence     

A Finite-element Model of Radial and Axial Conductivities for Individual Roots: Development and Validation for Two Desert Succulents

A morphologically explicit numerical model for analysing wateruptake by individual roots was developed based on a conductornetwork, with specific conductors representing axial or radialconductivities for discrete root segments. Hydraulic conductivity(L_p; m s^–1 MPa^–1) was measured for roots of Agavedeserti Engelm. and Opuntia ficus-indica (L.) Miller by applyinga partial vacuum to the proximal ends of excised roots in solution.L_p was also measured for 40- to 80-mm segments along a root,followed by measurements of axial conductivity and calculationof radial conductivity. Predicted values of L_p for entire rootsbased on two to ten segments per root averaged 1.04±0.07(mean±s.e. mean for n = 3) of the measured L_p for A.deserti and 1.06±0.10 for O. ficus-indica. The modelalso closely predicted the drop in water potential along theroot xylem (^xylem); when a tension of 50 kPa was applied tothe proximal ends of 0.2 m-long roots of A. deserti and O. ficus-indica,the measured ^xylem to midroot averaged 30 kPa compared witha predicted decrease of 36 kPa. Such steep gradients in ^xylemsuggest that the driving force for water movement from the soilto young distal roots may be relatively small. The model, whichagreed with an analytical solution for a simple hypotheticalsituation, can quantify situations without analytical solutions,such as when root and soil properties vary arbitrarily alonga root. Agave deserti, electrical circuit analog, hydraulic conductivity, Opuntia ficus-indica, water potential     

Unidirectional Ca2+ Fluxes in Roots of Rye (Secale cereale L). A Comparison of Excised Roots with Roots of Intact Plants

The unidirectional Ca²⁺ fluxes across the plasma membrane andtonoplast were determined in both excised roots and roots ofintact seedlings of rye (Secale cereale L. cv. Rheidol). Theunidirectional Ca²⁺ fluxes across the plasma membrane and tonoplastmeasured in excised roots were of a similar order of magnitudeto those determined in roots of intact plants. Influx and effluxof Ca²⁺ across the root plasma membrane were similar (estimatedto be between 0·7 and 3·4 µmol g     

The Effect of Combined Nitrogen on the Growth and Nodulation of Excised Roots of Phaseolus vulgaris L.

Isolated roots of Phaseolus vulgaris were grown in aseptic cultureusing a modified Raggio technique in which the organic nutrientsare fed to the cut (basal) end of the excised root while theroot tip grows into a mineral-salt solution inoculated withRhizobium. Treatments were applied to investigate the effectsof varying the level of sucrose in the organic medium and ofadding combined nitrogen as nitrate and urea to both media. There was a marked effect of sucrose on the growth and nodulationof the roots. Increasing the concentration increased the numberof nodules both per root and per unit fresh weight of tissue. The growth of the roots was not affected by the level of combinednitrogen. Nitrate in the mineral-salt solution markedly reducednodule numbers but in the agar medium it had only a slight delayingeffect on nodulation. Urea in either the mineral-salt solutionor the organic medium reduced nodule numbers though to a lesserextent than nitrate in the mineral-salt solution. The number of nodules formed was inversely correlated with thelevels of soluble and inorganic nitrogen compounds in the tissues. It is suggested that the adverse effect of combined nitrogenon nodulation is due to the accumulation of unsequestered nitrogencompounds and a depletion of carbohydrates generally withinthe root tissues rather than the local effect of any particularnitrogen compound.     

Water Influx Characteristics and Hydraulic Conductivity for Roots of Agave deserti Engelm.

Various plant and environmental factors influence the hydraulicproperties for roots, which were examined using negative hydrostaticpressures applied to the proximal ends of individual excisedroots of a common succulent perennial from the Sonoran Desert,Agave deserti Engelm. The root hydraulic conductivity, L^p, increasedsubstantially with temperature, the approximately 4-fold increasefrom 0.5°C to 40°C representing a Q¹⁰ of 1.45. Suchvariations in L_p with temperature must be taken into accountwhen modelling water uptake, as soil temperatures in the rootzone of such a shallow-rooted species vary substantially bothdaily and seasonally. At 20°C, L_p was 2.3 x 10^–7 ms^{macron}1MPa^{macron}1for 3-week-old roots, decreasing to abouthalf this value at 10 weeks and then becoming approximatelyhalved again at 6 months. For a given root age, L_p for rainroots that are induced by watering as lateral branches on theestablished roots (which arise from the stem base) was aboutthe same as L_p for established roots. Hence, the conventionalbelief that rain roots have a higher L_p than do establishedroots is more a reflection of root age, as the rain roots tendto be shed following drought and thus on average are much youngerthan are established roots. Unlike previous measurements onroot respiration, lowering the gas-phase oxygen concentrationfrom 21% to 0% or raising the carbon dioxide concentration from0.1% to 2% had no detectable effect on L_p for rain roots andestablished roots. L_p for rain roots and established roots wasdecreased by an average of 11% and 35% by lowering the soilwater potential from wet conditions (_soil=0 kPa) to {macron}40kPa and {macron}80 kPa, respectively. Such decreases in L_p mayreflect reduced water contact between soil particles and theroot surface and should be taken into account when predictingwater uptake by A. deserti. Key words: Gas phase, rain roots, root age, soil, temperature, water potential     

Studies on the Growth and Respiration of Roots: I. THE EFFECTS OF STIMULATORY AND INHIBITORY CONCENTRATIONS OF {beta}-INDOLYLACETIC ACID ON ROOT SECTIONS OF PISUM SATIVUM

Simultaneous observations on extension growth and respirationrate (oxygen consumption) of 2-mm. sections excised from theextension zone of roots of pea (Pisum sativum) growing in distilledwater and 0·5 per cent. sucrose have yielded resultsclosely similar to those of Brown and Sutcliffe (1950). Respirationrate is not obviously correlated with growth rate either inwater or in sucrose, but it is strongly correlated with sectionlength. Respiration rate per unit section length (¬per unitfresh weight) shows a marked downward drift during extensionand is affected little by growth conditions. Tentative suggestionsare advanced to account for the small differences between driftsin o·5 per cent. sucrose and those in distilled water. Medium agitation produces an immediate and sustained stimulationof growth but no stimulation of oxygen uptake until the latergrowth stages. Thus respiration per unit section length is unaffectedby agitation at any stage. A typical growth response to ß-indolylacetic acid(IAA) was obtained, with a maximum stimulation (of about 35per cent.) at 1 part in 10¹¹ and inhibitions increasing progressivelywith concentration beyond the threshold of about i part in 10⁹.Both percentage stimulation and percentage inhibition of growthwere independent of the presence of sucrose. Respiratory responses to ß-indolylacetic acid werecomplex. In water no immediate response could be detected witheither a growth-stimulatory (10^–11) or a growth-inhibitory(10^–-8) concentration, while in 0·5 per cent. sucrosethe inhibitory concentration prevented the small immediate respiratoryrise due to the sucrose, probably by impeding sugar entry. Duringthe subsequent period of rapid growth (up to 36 hours) the smallrespiratory responses observed closely followed the small growthresponses to both concentrations of IAA, suggesting that theformer are the direct result of the differences in section lengthinduced by the auxin. When growth ceases (at 48 hours) sectionswhich have grown considerably in sucrose show respiratory ratesstill closely correlated with section length, whereas in waterboth concentrations of auxin induce marked depressions in respirationrate. It is concluded that ß-indolylacetic acid in bothgrowth-stimulatory and growth- inhibitory concentrations hasno direct effect on the activity of the respiratory enzyme systemof growing root cells. The small respiratory responses are bestexplained as resulting from differential changes in sectionsize and correlated changes in the enzyme complements of thegrowing cell.     

The Carbohydrate Nutrition of Tomato Roots: V. The Promotion and Inhibition of Excised Root Growth by Various Sugars and Sugar Alcohols

Iron is only consistently present in an available form in White'sroot culture medium if the inorganic salts are autoclaved withthe sugar. The substitution of ferric ethylenediamine-tetra-acetatefor the inorganic ferric salt of White's medium ensures ironavailability when the carbon source of the medium is renderedsterile by ether treatment and subsequently added to the remainderof the constituents which have been sterilized by autoclaving. The biological activity of sugars, and particularly of dextroseand laevulose, is altered by autoclaving them in presence ofthe inorganic salt solution of White's medium. The only sugar which supports a considerable growth of excisedtomato roots is sucrose. The activity of this sugar is not affectedby alcohol-precipitation nor is it dependent upon the simultaneouspresence of traces of its constituent mono-saccharides. Dextrose or laevulose or a mixture of the two sugars supporta low but sustained level of excised-root growth. All othersugars and sugar alcohols tested were inactive as carbon sources. The addition of sucrose at low concentration (0–2 percent.) to a medium containing dextrose as the main carbon compounddoes not make possible a level of growth comparable with thatobtained with an adequate sucrose supply. It has not been possibleto enhance the growth-rate of excised roots supplied with dextroseby previous presentation of this sugar under conditions permittingactive growth. Using media containing 'etherized' sucrose anddextrose, no evidence was obtained of any competitive inhibitionof sucrose utilization by dextrose. Certain sugars when added to a medium, containing the optimumconcentration of sucrose₁, markedly inhibited excised root growth.Thus l-sorbose, l- and d-arabinose, and d-xylose caused notless than 80 per cent, inhibition at a concentration of 0-5per cent. d-mannose and d-galactose completely inhibited growthat o-1 per cent. The oligosaccharides, dextrose, laevulose,and the sugar alcohols tested had, by contrast, very low inhibitoryactivity.     

Effects of NO2 and O3 Alone or in Combination on Kidney Bean Plants (Phaseolus vulgaris L.): Growth, Partitioning of Assimilates and Root Activities

Ten-day old kidney bean plants (Phaseolus vulgaris L. cv. Shin-edogawa)were exposed to 2.0 and 4–0 parts 10^–6 NO2, and0.1, 0.2, and 0.4 parts 10^–6 O3 alone or in combinationfor 2, 4, and 7 d. The effects of these air pollutants wereexamined with respect to the growth, partitioning of assimilates,nitrogen uptake, soluble sugar content, and root respiration. Decreased dry matter production was significant with all treatmentsexcept 2.0 parts 10^–6 NO₂ and 0.1 parts 10^–6 O₃.Exposure to mixtures of the gases produced more severe suppressionof growth than exposure to the single gases. Root/shoot ratiowas significantly lowered at 7 d by the gas treatments otherthan 2.0 parts 10^–6 NO₂ and 0.1 parts 10^–6 O₃. Thetotal nitrogen content of plants was increased by all treatments;the higher percent of nitrogen found with O₃ exposure will resultfrom the growth retardation which increases the concentrationof nitrogen in the plants because the absorption of nitrogenby roots was unaffected. The combination of O₃ with NO₂ significantlydecreased the assimilation of NO₂ by the plants. The concentration of soluble sugars in roots was decreased bythe gas treatments. There was a strong positive correlationbetween soluble sugar content and dry weight of the roots harvestedat 7 d. Root respiration was relatively unchanged until 5 dand then decreased significantly at 7 d by 2.0 parts 10^–6NO₂ and 0–2 parts 10^–6 O₃. Retarded growth of theroots and the decreased root respiration may be due to diminishedtranslocation of sugars from leaves to roots caused by exposureto air pollutants. The uptake of soil nitrogen was not closelyrelated with root respiration in the case of O₃ exposure. Key words: NO₂, O₃, Phaseolus vulgaris, Growth, Sugars, Root respiration