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.     

Plant Growth in Relation to the Supply and Uptake of NO3-: A Comparison Between Relative Addition Rate and External Concentration as Driving Variables

Two approaches to quantifying relationships between nutrientsupply and plant growth were compared with respect to growth,partitioning, uptake and assimilation of NO₃^– by non-nodulatedpea (Pisum sativum L. cv. Marma). Plants grown in flowing solutionculture were supplied with NO₃^– at relative addition rates(RAR) of 0·03, 0·06, 0·12, and 0·18d^–1, or constant external concentrations ([NO₃^–)of 3, 10, 20, and 100 mmol m^–3 over 19 d. Following acclimation,relative growth rates (RGR)approached the corresponding RARbetween 0·03–0.12 d^-1, although growth was notlimited by N supply at RAR =0.18 d^-1. Growth rates showed littlechange with [NO₃–] between 10–100 mmol m^–3(RGR=0·15 –0·16 d^-1). The absence of growthlimitation over this range was suggested by high unit absorptionrates of NO₃^–, accumulation of NO₃^– in tissues andprogressive increases in shoot: root ratio. Rates of net uptakeof NO₃^– from 1 mol m^–3 solutions were assessed relativeto the growth-related requirement for NO₃^–, showing thatthe relative uptake capacity increased with RGR between 0·03–0·06d^–1 , but decreased thereafter to a theoretical minimumvalue at RGR     

Respiratory Efflux of Carbon Dioxide from Mature and Meristematic Tissue of Uniculm Barley During Eighty Hours of Continuous Darkness

Young plants of uniculm barley were grown singly in pots ina growth room at 23/21 °C, and an irradiance of 655 µEm^–2s^–1 during each 12 h photoperiod. At the fifth leaf stage,they were subjected to 80 h of continuous darkness during whichthe rates of CO₂ efflux of vegetative shoot meristems, and maturefully expanded leaves, were separately monitored. Respiratoryefflux from the meristematic tissue was initially high, 12–15mg CO₂ g^–1 h^–1, equivalent to a daily loss in weightof 20–25 per cent. It remained high, or even rose slightly,during what would have been the normal dark period, but thenfell sharply. Even so, it was still three times that of themature tissue at the end of the experimental period. The rateof CO₂ efflux of the mature tissue began low, and fell evenfurther during the first 12 h of darkness. It then levelledoff at a rate of 2·0–2·5 mg CO2 g^–1h^–1, equivalent to a daily loss in weight of about 3 percent. It is suggested that the rate of ‘mature tissue’respiration, established after 12–24 h of darkness, mightbe a useful selection criterion to employ in attempts to increasethe total dry matter yield of the grass crop by breeding. Hordeum vulgare L., barley, respiration, synthetic respiration, maintenance respiration, meristem, mature tissue respiration, simulated sward     

Effects of the fungal endophyte, Neotyphodium lolii, on net photosynthesis and growth rates of perennial ryegrass (Lolium perenne) are independent of In Planta endophyte concentration

• Background and Aims Neotyphodium lolii is a fungal endophyteof perennial ryegrass (Lolium perenne), improving grass fitnessthrough production of bioactive alkaloids. Neotyphodium speciescan also affect growth and physiology of their host grasses(family Poaceae, sub-family Pooideae), but little is known aboutthe mechanisms. This study examined the effect of N. lolii onnet photosynthesis (P_n) and growth rates in ryegrass genotypesdiffering in endophyte concentration in all leaf tissues. • Methods Plants from two ryegrass genotypes, Nui D andNui UIV, infected with N. lolii (E+) differing approx. 2-foldin endophyte concentration or uninfected clones thereof (E–)were grown in a controlled environment. For each genotype xendophyte treatment, plant growth rates were assessed as tilleringand leaf extension rates, and the light response of P_n, darkrespiration and transpiration measured in leaves of young (30–45d old) and old (>90 d old) plants with a single-chamber openinfrared gas-exchange system. • Key Results Neotyphodium lolii affected CO₂-limited ratesof P_n, which were approx. 17 % lower in E+ than E– plants(P < 0·05) in the young plants. Apparent photon yieldand dark respiration were unaffected by the endophyte (P >0·05). Neotyphodium lolii also decreased transpiration(P < 0·05), but only in complete darkness. There wereno endophyte effects on P_n in the old plants (P > 0·05).E+ plants grew faster immediately after replanting (P < 0·05),but had approx. 10 % lower growth rates during mid-log growth(P < 0·05) than E– plants, but there was noeffect on final plant biomass (P > 0·05). The endophyteeffects on P_n and growth tended to be more pronounced in NuiUIV, despite having a lower endophyte concentration than NuiD. • Conclusions Neotyphodium lolii affects CO₂ fixation,but not light interception and photochemistry of P_n. The impactof N. lolii on plant growth and photosynthesis is independentof endophyte concentration in the plant, suggesting that theendophyte mycelium is not simply an energy drain to the plant.However, the endophyte effects on P_n and plant growth are stronglydependent on the plant growth phase.     

Nitrogen Utilization in N-limited Barley During Vegetative and Generative Growth: III. POST-ANTHESIS KINETICS OF NET NITRATE UPTAKE AND THE ROLE OF THE RELATIVE ROOT SIZE IN DETERMINING THE CAPACITY FOR NITRATE ACQUISITION

Barley (Hordeum vulgare L., cvs Golf, Mette, and Laevigatum)was grown under nitrogen limitation in solution culture untilnear maturity. Three different nitrogen addition regimes wereused: in the ‘HN’ culture the relative rate of nitrate-Naddition (RA) was 0·08 d^–1 until day 48 and thendecreased stepwise to, finally, 0·005 d^–1 duringgrain-filling; the ‘LN’ culture received 45% ofthe nitrogen added in HN; the ‘CN’ culture was maintainedat RA 0·0375 d^–1 throughout. Kinetics of net nitrateuptake were measured during ontogeny at 30 to 150 mmol m^–3external nitrate. V_max (which is argued to reflect the maximuminflux rate in these plants) declined with age in both HN andLN cultures. A pronounced transient drop was observed just beforeanthesis, which correlated in time with a peak in root nitrateconcentration. Similar, but less pronounced, trends were observedin CN. The relative V_max (unit nitrogen taken up per unit nitrogenin plants and day) in all three cultures declined from 1·3–2·3d^–1 during vegetative growth to 0·1–0·7d^–1 during generative growth. These values are in HN andLN cultures 15- to more than 100-fold in excess of the demandset by growth rates throughout ontogeny. Predicted balancingnitrate concentrations (defined as the nitrate concentrationrequired to support the observed rate of growth) were below6·0 mmol m^–3 in HN and LN cultures before anthesisand then decreased during ontogeny. In CN cultures the balancingnitrate concentration increased during grain-filling. Apartfrom the transient decline during anthesis, most of the effectof ageing on relative V_max can be explained in terms of reducedcontribution of roots to total biomass (R:T). The loss in uptakeper unit root weight is largely compensated for by the declinewith time in average tissue nitrogen concentrations. The quantitativerelationships between relative V_max and R:T in ageing plantsare similar to those observed for vegetative plants culturedat different RAs. The data support the contention that the capacity for nitrateacquisition in N-limited plants is under general growth control,rather than controlled by specific regulation of the biochemicalpathway of nitrate assimilation. Key words: Barley, nitrogen concentration, root: total plant biomass ratio, V_max     

The Carbon Economy of Rubus chamaemorus L. II. Respiration

Respiratory activity and seasonal changes in carbohydrate contentof the storage organs of Rubus chamaemorus L. have been investigated.Leaf dark respiration rate increases in a non-linear mannerfrom 0·7 mg CO₂ evolved dm^–2 h^–1 at 0 °Cto 4·6 rng CO₂ evolved dm^–2 hh^–1 at 30 °C.Root and rhizome respiration rates increase from 1 µ1O₂ uptake g^–1 fresh weight h^–1 at 0.7 ° C to10 µ10, uptake g^–1 f. wt h^–1 at 20 °C.Rhizome carbohydrate reserves decline from a September peakof 33 per cent alcohol insoluble d. wt to 16 per cent in May. The circumpolar distribution of R. chamaemorus is discussedin relation to the evidence presented here and in the precedingpaper of the series.     

Components of Growth and Dark Respiration of Kikuyu (Pennisetum clandestinum Chiov.) at Various Temperatures

Growth and dark respiration were measured in dense, miniatureswards of kikuyu grass grown at constant temperatures of 15,20, 25 and 30 °C. Total respiration over the first 12 hof darkness was very high and CO² efflux per unit surface areavaried from 2.4 to 3.9 g CO₂ m^–2 h^–1 at 15 and 30°C respectively. Such rates were consistent with the correspondinglyhigh net growth rates of 24 and 63 g d. wt m^–2 d^–1and the heavy yields of herbage. When plants were kept in thedark, CO₂ efflux subsequently declined rapidly to a lower, constantrate which was taken to be the maintenance respiration rate.The half-life of the declining phase of respiration averaged10.9 and 6.0 h at 15 and 30 °C respectively, and was curvilinearlyrelated to the specific maintenance respiration rate (m). Therapid decline in respiration was consistent with the low concentrationsof total soluble carbohydrate and starch in the herbage. Valuesof m for lamina and top growth increased with temperature witha Q₁₀ of 2.6 and 1.42 respectively, but m of stems alone wasnot affected by temperature. Using results from this study forkikuyu and from McCree (1974) for sorghum and white clover,it was noted that all three species have similar m when grownat temperatures which are near their respective optimums forgrowth. Kikuyu, Pennisetum clandestinum, growth, respiration, temperature     

Estimating the Bioenergetic Cost of a Developing Kiwifruit Berry and its Growth and Maintenance Respiration Components

A response surface was developed by regression analysis to quantifythe seasonal respiratory losses by a kiwifruit [Actinidia deliciosa(A. Chev.) C. F. Liang et A. R. Ferguson var. deliciosa cv.Hayward] berry growing in Fresno, CA. The equation of the surfacewas LNRESP = 1·622 + 0·0697 x TEMP –0·0472x DAY + 0·000165 x DAYSQ, where LNRESP is the naturallogarithm of the respiration rate (nmol CO₂ g d. wt^–1s^–1), TEMP is fruit temperature (°C), DAY is the numberof days after flowering, and DAYSQ is the square of the numberof days after flowering. Respiratory losses for a fruit witha final dry mass of 18·5 g were calculated to be 5·57and 5·92 g glucose per fruit per season in 1985 and 1986,respectively. Maintenance respiration was estimated to be 2·84and 3·19 g glucose per fruit per season for 1985 and1986, respectively. The total calculated bioenergetic cost ofkiwifruit berry growth and respiration was 25·25 and25·60 g glucose per fruit per season for 1985 and 1986,respectively. Respiratory losses, expressed as a proportionof the total carbohydrate required for fruit growth, were significant(mean 22·6%). The cost of fruit growth was estimatedto be very similar for two cooler sites (Davis and Watsonville)but estimates of maintenance respiration based on Fresno fruitrespiration data were unrealistically low for the Watsonvillesite. Actinidia deliciosa (A. Chev.) C. F. Liang et A. R. Ferguson var. deliciosa cv. Hayward, kiwifruit, growth respiration, maintenance respiration, bioenergetic costs, model     

Carbohydrate Metabolism of Rice Seedlings Grown in Oxygen Deficient Solution

Atwell, B. J. and Greenway, H. 1987. Carbohydrate metabolismof rice seedlings grown in oxygen deficient solution.—J.exp. Bot. 38: 466–478. Rice seedlings (Oryza sativa L.) were grown in the dark forup to 4 d in solutions containing various concentrations ofO₂. The rate of depletion of the endosperm was most rapid inaerated solution (0·25 mol O₂ m^–3), largely dueto the inhibition of growth of seedlings at very low O₂ concentrations.Earlier suggestions that there is a deficit of sugars for growthand energy generation in O₂ deficient coleoptiles were tested. Coleoptiles, shaking in aerated solution, respired about one-thirdof the endogenous sugars to CO₂ and incorporated the rest intostructural compounds. In contrast, the proportion of carbonwhich went to growth in anoxia was very low. Consistent withthese results, endogenous sugar levels were generally highestat low O₂ concentrations. Even so, coleoptiles grown and testedas low as 0·03 mol O₂ m^–3 showed appreciable metabolismof exogenous ¹⁴C-glucose to CO₂, soluble and insoluble compounds,suggesting that a minimal O₂ supply was sufficient to sustainsome growth. Furthermore, glucose feeding caused little or norise in O₂ uptake or tissue sugar levels. Similarly, the specificactivity of the evolved CO₂ was not markedly different in coleoptilesgrowing at 0·03 and 0·25 mol O₂ m^–3 Further evidence was obtained to show that endogenous substrateswere adequate for growth and respiration at both low and highO₂ concentrations. Exogenous glucose and malate did not stimulateO₂ uptake at any stage of growth in aerated coleoptiles. Therewas sufficient endogenous substrate to sustain a 35–45%rise in O₂ uptake induced by uncoupling and enrichment withO₂. Exogenous glucose did not stimulate growth of intact seedlingsat any O₂ concentration. Key words: Rice seedlings, carbohydrate metabolism, oxygen deficient solution     

Normalizing Development of Cultured Triticum aestivum L. Embryos: I. LOW OXYGEN TENSIONS AND EXOGENOUS ABA

Wheat (Triticum aestivum L.) embryos form in dynamically-regulatedovular environments. Our objectives were to improve developmentof cultured immature wheat embryos by simulating, in vitro,abscisic acid (ABA) levels and O₂ tensions as found in wheatovules during zygotic embryogenesis. We characterized from intactwheat kernels embryo respiration, embryo morphology and embryoand endosperm + ABA levels at 13, 19 and 25 d post-anthesis(DPA). Young (13 DPA) embryos were then excised and culturedin vitro, where they were exposed to 0·2 or 2·Ommol m^–3 ±ABA and 2.·1, 2·5 or 7·4mol m^–3 (6, 7 and 21%, respectively) gaseous O₂. At 6and 12 d in culture, + ABA levels, embryo respiration and embryomorphology were characterized by treatment. Thirteen-day-oldembryos from two different plant populations differed by 17-foldin initial ABA content. However, this difference did not affectprecocious germination in vitro, nor did it affect the amountof exogenous ABA required to reduce precocious germination by40%. In this respect, embryos from both populations were equallysensitive to exogenous ABA. Cavity sap O₂ levels (2·1to 2·5 mol m^–3) were much more effective in preventingprecocious germination of cultured embryos than were cavitysap levels of ABA (0·2 to 2·0 mmol m^–3).The combination of physiological levels of both ABA and O₂ largelynormalized DW accumulation and embryo morphology without alteringendogenous + ABA levels. Residual respiration of cultured embryoswas higher than that of embryos grown in situ, and was not influencedby the exogenous O₂ and ABA treatments Key words: Abscisic acid, embryo development, oxygen tensions, respiration, wheat     

Comparisons of the Respiratory Effluxes of Nodules and Roots in Six Temperate Legumes

The specific respiration rates of nodulated root systems, ofnodules and of roots were determined during active nitrogenfixation in soya bean, navy bean, pea, lucerne, red clover andwhite clover, by measurements on whole plants before and afterthe removal of nodule populations. Similar measurements weremade on comparable populations of the six legumes, lacking nodulesbut receiving abundant nitrate-nitrogen, to determine the specificrespiration of their roots. All plants were grown in a controlled-environmentclimate which fostered rapid growth. The specific respiration rates of nodulated root systems ofthe three grain and three forage legumes during a 7–14-dayperiod of vegetative growth varied between 10 and 17 mg CO₂g^–1 (dry weight) h^–1. This mean value consistedof two components: a specific root respiration rate of 6–9mg CO₂ g^–1 h^–1 and a specific nodule respirationrate of 22–46 mg CO₂ g^–1 h^–1. Nodule respirationaccounted for 42–70 per cent of nodulated root respiration;nodule weight accounted for 12–40 per cent of nodulatedroot weight. The specific respiration rates of roots lackingnodules and utilizing nitrate nitrogen were generally 20–30per cent greater than the equivalent rates of roots from nodulatedplants. The measured respiratory effluxes are discussed in thecontext of nitrogen nitrogen fixation, nitrate assimilation. Glycine max, Phaseolus vulgaris, Pisum sativum, Medicago sativa, Trifolium pratense, Trifolium repens, soya bean, navy bean, pea, lucerne, red clover, white clover, nodule respiration, root respiration, fixation, nitrate assimilation     

Effects of Prolonged Darkness on the Sensitivity of Leaf Respiration to Carbon Dioxide Concentration in C3and C4Species

Predicting responses of plant and global carbon balance to theincreasing concentration of carbon dioxide in the atmosphererequires an understanding of the response of plant respirationto carbon dioxide concentration ([CO₂]). Direct effects of thecarbon dioxide concentration at which rates of respiration ofplant tissue are measured are quite variable and their effectsremain controversial. One possible source of variation in responsivenessis the energy status of the tissue, which could influence thecontrol coefficients of enzymes, such as cytochrome-c oxidase,whose activity is sensitive to [CO₂]. In this study we comparedresponses of respiration rate to [CO₂] over the range of 60to 1000 µmol mol^-1in fully expanded leaves of four C₃andfour C₄herbaceous species. Responses were measured near themiddle of the normal 10 h dark period, and also after another24 h of darkness. On average, rates of respiration were reducedabout 70% by the prolonged dark period, and leaf dry mass perunit area decreased about 30%. In all species studied, the relativedecrease in respiration rate with increasing [CO₂] was largerafter prolonged darkness. In the C₃species, rates measured at1000 µmol mol^-1CO₂averaged 0.89 of those measured at 60µmol mol^-1in the middle of the normal dark period, and0.70-times when measured after prolonged darkness. In the C₄species,rates measured at 1000 µmol mol^-1CO₂averaged 0.79 of thoseat 60 µmol mol^-1CO₂in the middle of the normal dark period,and 0.51-times when measured after prolonged darkness. In threeof the C₃species and one of the C₄species, the decrease in theabsolute respiration rate between 60 and 1000 µmol mol^-1CO₂wasessentially the same in the middle of the normal night periodand after prolonged darkness. In the other species, the decreasein the absolute rate of respiration with increase in [CO₂] wassubstantially less after prolonged darkness than in the middleof the normal night period. These results indicated that increasingthe [CO₂] at the time of measurement decreased respiration inall species examined, and that this effect was relatively largerin tissues in which the respiration rate was substrate-limited.The larger relative effect of [CO₂] on respiration in tissuesafter prolonged darkness is evidence against a controlling roleof cytochrome-c oxidase in the direct effects of [CO₂] on respiration.Copyright 2001 Annals of Botany Company Carbon dioxide, respiration, Abutilon theophrasti(L.), Amaranthus retroflexus(L.),Amaranthus hypochondriacus (L.), Datura stramonium(L.), Helianthus annuus(L.), Solanum melongena(L.), Sorghum bicolor(L. Moench), Zea mays     

Respiration and Phloem Translocation in the Roots of Chickpea (Cicer arietinum)

Root growth in chickpea (Cicer arietinum) has been studied fromthe early vegetative phase to the reproductive stage in orderto elucidate its growth and maintenance respiration and to quantifythe translocation of assimilates from shoot to root. A carbonbalance has been drawn for this purpose using the growth andrespiration data. The increase in the sieve tube cross-sectionalarea was also followed simultaneously. Plants growing in a nutrient culture medium were studied todetermine the relative growth rate (RGR) 5–60 d aftergermination. RGR declined from 113 to 41 mg d^–1 g^–1during the measurement period. Simultaneous with the RGR analysis,respiration rate was also measured using an oxygen electrode.The respiration rate declined as the plants aged and a drasticreduction was recorded following anthesis. The relationshipbetween RGR and respiration rate was used to extrapolate themaintenance respiration (m) and growth respiration (1/Y_EG).The respiration quotient (r.q.) of the roots was 1.2 and theQ₁₀ in the range 20–25 °C was 2·2. A carbon balance for the roots was constructed by subtractingthe carbon lost during respiration from that gained during growth.The roots were found to respire no less than 80% of the carbontranslocated. The increase in the cross-sectional area composed of sieve tubeswas measured near the root-shoot junction as the plants grew.Chickpea has storied sieve plates which simplifies these measurements.Their cross-sectional area increased during growth mainly becauseof an increase in sieve tube number. The diameter of individualsieve tubes remained constant. Specific mass transfer (SMT) values for seive tubes into theroots have been computed during various stages of growth. SMTvalues were relatively constant before anthesis (approx. 6·5g h^–1 cm^–2), but decreased following anthesis. Wedid not evaluate possible retranslocation from roots: any suchretranslocation would have the effect of increasing our SMTvalues. Chickpea, Cicer arietinum, legume, root, respiration, phloem, translocation, carbon balance, specific mass transfer, sieve-tube dimensions     

Microbiological Synthesis of Fat: THE EFFECTS OF NITROGEN LEVEL ON THE METABOLISM OF PENICILLIUM LILACINUM THOM IN A SUCROSE MEDIUM

1. A study has been made of the relationships between the synthesesof carbohydrate, protein, and fat by Penicillium lilacinum Thomin presence of different amounts of sodium nitrate us a definedsucrose salts medium.
2. Under the defined experimental conditionsincreases in the concentrationof NO^–₂ in the medium werefollowed by increases in therates at which nitrogen and sugarwere taken up by the fungus,in the quantities assimilated,and in total and protein nitrogenin the felt. These conditionsprevailed so long as unassimilatedsugar was available.
3. Mediaof lower NO^–₃ concentration (for example, 0·32or 0·64 per cent. (w/v) NaNO^–₂;) yielded feltsricher in carbohydrate than were those grown in media of higherNO^–₂; content (0·96 or 1·28 per cent. (w/v)NaNO₃ The carbohydrate content of the felts increased graduallyuntil the sugar in the medium was exhausted; carbohydrate contentthen decreased.
4. Media of lower NO^–₃; concentration weremore conduciveto fat synthesis than those of higher NO^–₃;content.

     

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     

The Influence of NO-3 and NH+4 Nutrition on the Gas Exchange Characteristics of the Roots of Wheat (Triticum aestivum) and Maize (Zea mays) Plants

Respiratory oxygen consumption by roots was 1·4- and1·6-fold larger in NH⁺₄-fed than in NO^-₃-fed wheat (Triticumaestivum L.) and maize (Zea mays L.) plants respectively. Higherroot oxygen consumption in NH⁺₄-fed plants than in NO^-₃-fedplants was associated with higher total nitrogen contents inNH⁺4-fed plants. Root oxygen consumption was, however, not correlatedwith growth rates or shoot:root ratios. Carbon dioxide releasewas 1·4- and 1·2-fold larger in NO⁺3-fed thanin NH⁺₄-fed wheat and maize plants respectively. Differencesin oxygen and carbon dioxide gas exchange rates resulted inthe gas exchange quotients of NH^-₄-fed plants (wheat, 0·5;maize, 0·6) being greatly reduced compared with thoseof NO^-₃-fed plants (wheat, 1·0; maize, 1·1). Measuredrates of HCO^-₃ assimilation by PEPc in roots were considerablylarger in 4 mM NH⁺₄-fed than in 4 NO^-₃ plants (wheat, 2·6-fold;maize, 8·3-fold). These differences were, however, insufficientto account for the observed differences in root carbon dioxideflux and it is probable that HCO^-₃ uptake is also importantin determining carbon dioxide fluxes. Thus reduced root extension in NH⁺₄-fed compared with NO^-₃-fedwheat plants could not be ascribed to differences in carbondioxide losses from roots.Copyright 1993, 1999 Academic Press Triticum aestivum, wheat, Zea mays, maize assimilation, ammonium assimilation, root respiration     

Nitrate-Ammonium Ratio Required for pH Homeostasis in Hydroponically Grown Soybean

Imsande, J. 1986. Nitrate-ammonium ratio required for pH homeostasisin hydroponically grown soybean.—J. exp. Bot. 37: 341–347. Plant acid-base homeostasis is achieved when the mmoles of hydroxylions produced in the plant equal the mmoles of protons. Reductionof nitrate to ammonia is the major source of hydroxyl ions whereasammonium uptake-assimilation and the metabolism of neutral sugarsto organic acids are the primary sources of protons. Soybean[Glycine max (L.) Merr plants were grown hydroponically on mediumsupplemented with 3·0 mol m^–3 nitrogen providedas various combinations of KNO₃ and NH₄NO₃ Plant growth consumedessentially all available nitrogen in each case; however, onlyin flasks supplemented with approximately 1·8 minolesof KNO₃ plus 0·6 mmole of NH₄NO₃ was the pH of the mediumunchanged. Thus, for every mmole of nitrogen assimilated, approximately0·6 mmole of dissociable protons must have been producedby the conversion of neutral sugars to carboxylic acids. Also,it was shown that a plant obtaining all of its nitrogen fromnitrate must neutralize or excrete approximately 0·5mmole of hydroxyl ion d^–1. Conversely, the plant derivingall of its nitrogen from dinitrogen must excrete or neutralizeat least 0·8 mmole of hydrogen ion d^–1 whereasthe plant deriving all of its nitrogen from aminonium must excreteor neutralize approximately 2·1 mmoles of hydrogen iond^–1. Nevertheless, plants grown on medium supplementedwith 2·4 mol m^–1 nitrate plus 0·6 mol m^–3ammonium did not achieve a higher growth rate than plants grownon 3·0 mol m^–3 nitrate. Key words: Glycine max, nitrogen fixation, nitrate utilization     

Allocation of Organ Biomass in Perfect and Imperfect Flowers

Perianth M_P, gynoecium M_G, and androecium M_A dry-weight biomass(in g) of 39 species of perfect flowers was measured. Thesedata were pooled with published data from an additional 51 speciesand used to determine size-dependent variations in (M_G and M_A)in terms of the hypothesis that the quotient of M_G and M_A exceeds1·0 for out-breeding (xenogamous) species and less than1·0 for in-breeding (autogamous) species. Ordinary leastsquare regression of the pooled data (n = 90) showed M_G = 0·118M^0·916_P (r² = 0·884) and M_A = 0·186 M^0·975_P(r² = 0·865), indicating that the biomass of the gynoeciumproportionally decrease as floral size increases. The exponentsof these regressions indicate that the ratio of gynoecial toandroecial biomass decreased with increasing floral size suchthat comparatively small flowers (M_P < 0·0021 g) hadM_G/M_A > 1·0 (predicted for 'out-breeders') while comparativelylarger flowers (M_P > 0·0021 g) had M_G /M_A < 1·0(predicted for 'in-breeders'). Thus, on average, the type ofbreeding system was a size-dependent phenomenon. To test whether the biomass of a floral organ-type is a legitimateindicator of gender reproductive effort, the biomass (in g)of stamen filaments M_m and anther sacs M_AS of 39 species wasdetermined. Least square regression of these data showed M_AS= 0·188 M^0·854_fil (r² = 0·967), indicatingthat species with larger stamen filaments, on the average, boreproportionally smaller anther sacs and thereby cautioning againstthe uncritical use of the allocation of biomass to floral organ-typeas a strict gauge of gender-function investment. To determine whether the loss of one gender-function resultsin proportional reallocation of biomass to the remaining gender-function,the size-dependency of androecial and gynoecial biomass wasdetermined for a total of 33 perfect and imperfect flowers ofCucumis melo. Regression of the data obtained from perfect flowersyielded M_A = 0·402 M^1·47_P (r² = 0·898)and M_G = 4·63 M^1·36_P (r² = 0·842). SinceM_G/M_A M^0·11_P , the biomass allocation to the gynoeciumrelative to the androecium decreased with increasing floralsize. This result was consistent with the broad interpecificcomparison based on 90 species with perfect flowers . Regressionof the data for imperfect flowers yielded M_A = 0·151M^1·02_P (r² = 0·675) and M_G = 4·68 M^1·47_P(r² = 0·996), indicating a near allometric relation forthe androecium and a strong positive anisometry for the gynoecium.Thus, for flowers of comparable size, a loss of female genderobtains a modest to significant again in androecial biomasswhereas the loss of male gender yields only a slight increasein gynoecial biomass. Collectively, the results of these studies indicate that biomassallocation patterns are size-dependent phenomena whose complexitieshave been largely ignored in the literature.Copyright 1993,1999 Academic Press Allometry, floral biomass, reproduction     

Defoliation in White Clover: Nodule Metabolism, Nodule Growth and Maintenance, and Nitrogenase Functioning During Growth and Regrowth

In two experiments, the functioning and metabolism of nodulesof white clover, following a defoliation which removed abouthalf the shoot tissue, were compared with those of undefoliatedplants. In one experiment, the specific respiration rates of nodulesfrom undefoliated plants varied between 1160 and 1830 µmolCO₂ g^–1h^–1, of which nodule ‘growth and maintenance’accounted for 22 ± 2 per cent, or 27 ± 3.6 percent, according to method of calculation. Defoliation reducedspecific nodule respiration and nodule ‘growth and maintenance’respiration by 60–70 per cent, and rate of N₂ fixationby a similar proportion. The original rate of nodule metabolismwas re-established after about 5 d of regrowth; during regrowthnodule respiration was quantitatively related to rate of N₂,fixation: 9.1 µmol CO₂ µmol^–1N₂. With the possible exception of nodules examined 24 h after defoliation,the efficiency of energy utilization in nitrogenase functioningin both experiments was the same in defoliated and undefoliatedplants: 2.0±0.1 µmol CO₂ µmol^–1 C₂H₄;similarly, there was no change in the efficiency of nitrogenasefunctioning as rate of N₂ fixation increased with plant growthfrom 1 to 22 µmol N₂ per plant h^–1. Exposure of nodulated white clover root systems to a 10 percent acetylene gas mixture resulted in a sharp peak in rateof ethylene production after 1.5–2.5 min; subsequently,rate of ethylene production declined rapidly before stabilisingafter 0.5–1 h at a rate about 50 per cent of that initiallyobserved. Regression of ‘peak’ rate of ethyleneproduction on rate of N₂ fixation indicated a value of 2.9 µmolC₂H₄ µmol^–1 N₂, for rates of N₂ fixation between1 and 22 µmol N₂ per plant h^–1. The relationshipsbetween nitrogenase respiration, acetylene reduction rates andN₂ fixation rates are discussed. Trifolium repens, white clover, defoliation, nodule respiration, N₂, fixation, nitrogenase     

ERRATA

On page 235, Table I: Equation (1) for Node 4 should read ‘A/A_c=0·840+0·0006A_c’;Equation (2) for Node 4 should read ‘A=0·89A_c’and Equation (2) for Node 5–10 should read ‘A=0·813A_c’.