The Fate of the Dry Matter, Carbohydrates and 14C Lost from the Leaves and Stems of Wheat during Grain Filling

In a field study with six winter wheat genotypes losses of drymatter from the stems between 30 June and maturity averaged172 g m^–2 (range 82–236), there being significantdifferences in loss between genotypes. Respiration from thestems during the same period was estimated to amount to 106g m^–2 (range 104–225). The amount of dry mattermobilized from the stems, calculated by difference, was estimatedas 66 g m^–2. The loss of ethanol- and water-soluble carbohydratefrom the stems (170 g m^–2; range 124–215) was verysimilar to the dry weight loss. Carbon-14 labelling was used to trace the time course and theamount of the movement of assimilates from the vegetative organsto the grain. Only 14•3 per cent (range 10•3–21•0)of the products of photosynthesis over the period 21 May-20June were relocated to the grains. This relocation amountedto an average of 7 per cent (range 5•7–11•4)of the final grain weight. It was estimated that during the18 days following anthesis on 20 June photosynthesis contributed48 per cent (range 39–55) of the final grain dry weight.Of this, about half was translocated to the grain within 10days of initial assimilation. The remainder appeared to be storedtemporarily in the stems and leaves and translocated to thegrains during the period 17–29 July. In general, relocationof dry matter from the vegetative organs to the grains, assessedby carbon-14 labelling, was greatest in those genotypes (Hobbitand Sportsman) which lost most dry weight from the stems andleaves.     

Sink Activity Estimation by Sink Size and Dry Matter Increase During the Ripening Stage of Barley (Hordeum vu/gare) and Rice (Oryza sativa)

During the ripening stage of barley and rice, the sink activitywas defined as the dry matter increase per units sink size,leaf area and time, as follows: NAR = A.SinkW+NAR', where NAR is the net assimilation rate (g d.wt dm^–2d^–1);A is the sink activity [g d.wt g^–1d.wt (ear) dm^–2d^–1]; Sink W is ear wt per plant at heading (g d.wt);and NAR' is net assimilation rate excluding the assimilate ofsink organ (g d.wt dm^–2 d^–1). Plant material with 16 combinations of mutually different sink(ear) and source (leaf) size were produced at heading for eachcrop: parts of each leaf and ear were removed to produce fourgrades in barley, and also a part of each leaf was removed producingfour grades for four rice varieties showing different ear size.NAR and NAR' were determined during 26 and 21 d in barley andrice after heading, respectively. Sink activity (A), representedas the assimilation rate induced by the sink organ, was estimatedfrom the relationship between SinkW and NAR using the previousequation. The sink activity was significantly higher in ricewith a value of 0–0.028 g d.wt g^–1 d.wt (ear) dm^–2d^–1 vs. 0–0.0017 in barley, suggesting that therelative role of leaves for grain filling is considerably higherin rice than in barley. The sink activity obtained in the studymight be introduced into a model to predict the yields of barleyand rice. Hordeum vulgare L, barley, Oryza saliva L, rice, dry matter, NAR, sink, source, sink activity, model     

Influence of Genotype and Environment on Growth of Barley Embryos in vitro

Isolated embryos of three contrasting barley genotypes werecultured in vitro on a range of media comprising 16 combinationsof sucrose (3–12 per cent) and 2, 4-D (0–8 mg 1^–1)concentration. Cultures were incubated at a range of temperaturesfrom 5 to 25°C and were examined after 21 days when shootlengths as well as fresh and dry weights were recorded. Therelative influence on growth of increasing concentrations ofsucrose and 2, 4-D was investigated, as was their interactionwith the incubation temperature. The genotypes were found todiffer markedly in their response to these two media components,with each parameter of growth differentially affected. Resultsare discussed in relation to the known dormancy characteristicsof these genotypes. Hordeum vulgare L., barley, embryo, dormancy, 2, 4-dichlorophenoxy acetic acid, sucrose     

Microclimate, Photosynthesis and Growth of Lucerne (Medicago sativa L.). II. Canopy Structure and Growth

The growth of lucerne var. Europe was examined in the fieldduring 1976. The annual dry matter production of unirrigatedlucerne during 1976, with no nitrogen fertilizer application,was 82.5 per cent greater than unirrigated S.24 perennial ryegrass,with a nitrogen application of 384 kg ha^–1. The mean aboveground growth rate of lucerne was 7.3 g DM m^–2 day^–1between March and early June, of which stem material contributeda maximum of 76.5 per cent. Significant losses of leaves andstems occurred from the end of April, indicating a loss of potentialforage material. Nitrogen analyses of the above ground crop suggested that in56 days lucerne yielded 10.7 per cent more nitrogen than didS.24 annually with a nitrogen fertilizer addition of 280 kgha^–1. Between 13 and 57 per cent of the daily photosynthate is translocatedbelow ground. Medicago sativaL, lucerne, dry matter production, canopy structure, nitrogen analyses     

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     

Specific Leaf Weight in Zones of Cell Division, Elongation and Maturation in Tall Fescue Leaf Blades

Patterns of change in specific leaf weight (SLW), water-solublecarbohydrate (WSC) content and leaf width were used to delineatethe region of secondary cell wall accumulation, and determinethe rate of increase in structural material along a developingleaf blade of tall fescue (Festuca arundinacea Schreb.). Structuralspecific leaf weight (SSLW) was determined by subtracting WSCmass from dry weight to emphasize structural material. Becausemeristematic activity, cell elongation, and cellular maturationare arranged successively in the grass leaf, these patternsrepresent a developmental sequence through which each segmentof the leaf blade passes. Patterns were generally similar fortwo genotypes, one selected for high (HYT) and the other forlow (LYT) yield per tiller, for a single genotype grown at 17or 25 C, and for two field-grown populations which differedin leaf area expansion rate (LAER). In all three studies, the elongation zone of the developingleaf had 31 to 39 per cent WSC on a dry weight basis. The LYTgenotype had a higher SLW at all stages of development whengrown at 17 than at 25 C, due to greater WSC accumulation.At 20 C, the HYT genotype had a higher SLW all along the elongatingleaf blade than the LYT genotype. This difference was due toa difference in SSLW, while WSC content was similar. The LERwas 64 per cent higher in the high population than the low,but elongation zones were similar in WSC. In all cases, SSLWwas high in the meristematic region, lowest near the distalend of the cell elongation zone, then increased linearly astissue matured. Rate of increase in SSLW was 8.5 and 5.2 g m^–2d^–1 for the HYT and LYT genotypes, respectively, and 7.6and 6.7 g m^–2 d^–1 for the high and low LAER populations,respectively. Festuca arundinacea Schreb., tall fescue, specific leaf weight, leaf width, water-soluble carbohydrates, leaf elongation rate     

Short-term Products of 14C-acetate Assimilation by Chlorella pyrenoidosa in the Light

The kinetics of ¹⁴C-2-acetate assimilation by Chlorella pyrenoidosain the light were examined. Under aerobic conditions the primaryproduct of acetate assimilation was succinic acid which, afterten seconds, contained over 60 per cent of the ¹⁴C incorporatedby the cells. The percentage of the total ¹⁴C in succinate fellwith time, while that in citrate and glutamate increased. After1800 sec over 60 per cent of ¹⁴C was present in two compounds,glutamic acid and an unknown compound (X). Glucose-6-phosphate,fructose-6-phosphate, phosphoglyceric acid and phosphoenolpyruvicacid became labelled after 60 sec but together never containedmore than one per cent of the total ¹⁴C incorporated. Underanaerobic conditions succinate was still the primary productof acetate assimilation, and the absence of carbon dioxide resultedin a decrease in ¹⁴C incorporation into compound X. The patternof acetate assimilation in acetate grown and acetate adaptedChlorella was very similar to that in photo-autotrophicallygrown Chlorella. In the presence of 10^–6M DCMU, succinicacid was the primary product of acetate assimilation, but therewas an early Incorporation of ¹⁴C into glutamate, aspartate,and malate. 4 x10^–3M MFA did not effect the early incorporationof ¹⁴C into succinic acid, but resulted in accumulation of ¹⁴Cin citrate and a decreased amount in glutamate and in compound X.     

Flavanoids in Pollen and Stigma of Brassica oleracea and Their Effects on Pollen Germination In Vitro

Brassica oleracea pollen was applied to a basic medium of 1.5per cent agar and 15 per cent sucrose to which flavanoids wereadded at three concentrations. Two types of agar were used;with agar 1, quercetin at a concentration of 0.5 x 10^–3per cent gave an increase in percentage germinating grains.With agar 2, an increase in germination occurred with kaempferoland naringin at concentrations of 0.5 x 10^–3 and 0.5 x10^–1 per cent respectively. Increase in pollen tube lengthoccurred with agar 2 and quercetin at a concentration of 0.5x 10^–3 per cent. The stigma tissue of B. oleracea contains at least three andthe pollen at least one glycoside of quercetin. The sugars inthe glycosides were not identified. Pollen germination and pollentube extension were not stimulated exclusively by the flavanoidspresent in the stigma. The flavanoid composition of the stigmadid not vary amongst five different S-allele genotypes, indicatingthat flavanoids are probably not directly involved in the incompatibilityreaction of B. oleracea.     

Photosynthesis of Ears and Flag Leaves of Wheat and Barley

Immediately after anthesis ears of spring wheat absorbed lessthan 0.5 mg CO₂, per hour in daylight and later evolved CO₂,in the light and in the dark. The rate of apparent photosynthesisof the combined flag-leaf lamina and sheath and peduncle (collectivelycalled flag leaf) of two spring wheat varieties, Atle and JufyI, was 3–4 mg per hour; the rates of the flag leaf andthe ear of two spring barleys, Plumage Archer and Proctor, wereeach about 1 mg per hour. The gas exchange of ears and flag leaves between ear emergenceand maturity accounted for most of the final grain dry weight.The CO₂, fixed by the wheat ear was equivalent to between 17and 30 per cent of the grain weight, but more than this waslost by respiration, so assimilation in the flag leaf was equivalentto 110–20 per cent of the final grain weight. In barley,photosynthesis in the flag leaf and the net CO₂ uptake by theear each provided about half of the carbohydrate in the grain. Barley ears photosynthesized more than wheat ears because oftheir greater surface, and flag leaves of wheat photosynthesizedmore than those of barley because they had more surface anda slightly greater rate of photosynthesis per dm².     

The Production and Distribution of Dry Matter in Maize after Flowering

An experiment in which different groups of leaf laminae wereremoved, or ears shaded, shortly after silking showed that mostof the dry-matter increase after flowering was produced by upperleaves. The top five, the middle four, and the bottom six laminaeaccounted, respectively, for 26 per cent, 42 per cent, and 32per cent of the leaf area duration (D) of the laminae afterflowering; the estimated contributions of the three groups todry-matter production by the laminae after flowering were about40 per cent, 35–50 per cent, and 5–25 per cent,respectively. The sheaths provided about one-fifth of the totalleaf area and probably contributed about one-fifth, and laminaefour-fifths, of the total dry matter produced after flowering.The contribution from photosynthesis by the ear was negligible,presumably because its surface area was only 2 per cent of thatof the leaves. Leaf efficiency (dry matter produced per unitarea) decreased greatly from the top to the base of the shoot.When laminae were removed, the grain received a larger fractionof the dry matter accumulated after flowering, less dry matterremained in the stem, and the photosynthetic efficiency of theremaining leaves was apparently increased. When alternate laminae were removed at the time of silking (half-defoliation)D was decreased by 40 per cent, and the subsequent productionof dry matter decreased nearly proportionately, so that netassimilation rate (E) was not affected but grain dry weightwas decreased by only 32 per cent. At the final harvest, thegrain of half-defoliated plants constituted 80 per cent of thedry matter accumulated after flowering, compared with 65 percent for intact plants. Stem weight decreased from two weeksafter flowering in half-defoliated plants, but remained nearlyconstant in intact plants. When pollination was prevented andno grains formed, E during the first month after flowering wasunaffected; the dry matter that would have passed into the grainaccumulated in the stem and husks, not in the leaves. The decrease in stem weight caused by defoliation suggests thatpreviously stored dry matter was moved to the grain. That suchmovement is possible was shown by keeping prematurely harvestedshoots in the dark for two weeks with their cut ends in water;the dry weight of the grain increased and that of the stem,laminae, husks, and core decreased. Nevertheless, dry-matterproduction after flowering was more than sufficient for graingrowth, and previous photosynthesis probably contributed littleto the grain.     

Nitrogen Fixation in the Phyllosphere of Tropical Plants: Occurrence of Phyllosphere Nitrogen-Fixing Micro-organisms in Eastern India and their Utility for the Growth and Nitrogen Nutrition of Host Plants

Of the 560 leaf samples belonging to 259 species of green plantsexamined more than 50 per cent of the Angiosperms and 25 percent of the Pteridophytes and Gymnosperms revealed the presenceof N₂-fixing micro-organisms in their phyllosphere. Plants particularlyremarkable in this respect are orchids and several other epiphytes,Scindapsus officinalis, Ficus and cucurbits. Most of the isolatesappear to be biotypes of Klebsiella pneumoniae. The more activestrains fixed more than 5 mg N g^–1 glucose utilized andreduced more than 100 nmol C₂H₂ mg^–1 cell d. w h^–1. The efficacy of the phyllosphere N₂-fixing isolates for N-nutritionof host plants was studied by spraying suspensions of the culturesgrown on N-free media on rice and wheat seedlings. In IR-26rice or Sonalika and Janak wheat grown on soil in wooden flatsor earthenware pots, 22 per cent of the 161 cultures studiedcaused increased height and about three-quarters of the culturesenhanced dry weight by more than 50 per cent; chlorophyll andN-contents were enhanced more than 50 per cent by about halfand two-thirds of the cultures respectively. In N-free sandculture 26 of the 50 promising strains doubled N-content, and30 doubled dry weight of the tested plants. In some cases dryweight, number of grains per panicle, and 1000 grain weightwere increased by 300, 70–83 and 126–158 per centrespectively; N-content of straw and seed was increased three-or fourfold. In several cases the beneficial effects were foundto match closely the performance of plants receiving ammoniumsulphate. Nitrogen-fixing micro-organisms, nitrogen nutrition, phyllosphere, rice, tropical plants, wheat     

Studies in the Nutrition of Apple Rootstocks: II. Effects of Concentration of Iron in the Nutrient Solution on Growth and Chlorophyll Content

Rooted one-year shoots were grown for one season by sprayingtheir roots with nutrient solution. Iron supplied as Fe-EDTAat four concentrations resulted in plants which were respectively(a) severely chlorotic, (b) mildly chlorotic, (c) dark greenand healthy (controls), and (d) dark green but with slight reductionin growth. Severely deficient plants showed 40–70 per cent reductionsin growth as measured by fresh weight, shoot length, diameterincrease, leaf area, net assimilation and relative growth-rates.Dry weights were reduced 70–80 per cent and of the totaldry-weight increment a greater proportion remained in the leaves,which had a lower dry weight and higher water content per unitarea. However, because the initial old stem formed a greaterproportion of the total dry weight, the leaf area ratio remainedabout 11 per cent lower than in the controls. Severely deficientplants had, per unit of chlorophyll, a higher dry-weight increaseand net assimilation rate than the controls. Mild deficiency caused 10–20 per cent reductions in growthand net assimilation rate; the leaf area ratio was normal. Possible mechanisms of the effects of low iron supply are discussed,while the small growth reduction at the highest Fe-EDTA concentrationis attributed to chelate toxicity     

Daily changes in population structure and production of Eudiapomus gracilis (G.O. Sars) (Copepoda, Calanoida) during summer in a shallow lake (Balaton, Hungary)

Population structure and production of Eudiaptomus gracilis(G.O. Sars) have been calculated from daily measurements inLake Balaton for one month during each summer in 1975 and 1977.Fecundity was different in the two years 6.98 ? 1.16 and 10.68? 1.42 in 1975 and 1977, respectively. A total of 80% and 64%of the population were made up of larvae in 1975 and 1977, respectively.The ratio of males to females was 1:1.63 and 1:1.1, respectively.In 1975 it was possible to follow the development of cohorts,19 –20 days in the former year, 17 –20 days in thelatter. In both years of examination 80 – 83% of naupliiand 12–15% of copepodites were eliminated. Daily net biomassproduction was 6.88 mg (dry wt.)/m³ in 1975 and 1.94 mg (drywt.)/m³ in 1977. Ratios of eggs, nauplii and copepodites indaily production was 1:2.4:1.4 in 1975 and 1:1.0:1.0 in 1977.The daily potential biomass production were 34.40 mg (dry wt.)/m³ and 10.28 mg (dry wt.)/m³ and the elimination were 80 and81 wt.%, respectively. P/B ratio — allowing for net productionvalues — was nearly the same in both periods of investigation(0.12 and 0.099 respectively).     

Carbon and Nitrogen Assimilation by Vicia faba L. at Low Temperature: the Importance of Concentration and Form of Applied-N

Low temperature (6 C) growth was examined in two cultivarsof Vicia faba L. supplied with 4 and 20 mol m^–3 N as nitrateor urea. Both cultivars showed similar growth responses to increasedapplied-N concentration regardless of N-form. Total leaf areaincreased, as did root, stem and leaf dry weight, total carboncontent and total nitrogen content. In contrast to findingsat higher growth temperatures, 20 mol m^–3 urea-N gavesubstantially greater growth (all parameters measured) than20 mol m^–3 nitrate-N. The increased carbon content per plant associated with increasedapplied nitrate or urea concentration, or with urea in comparisonto nitrate, was due to a greater leaf area per plant for CO₂uptake and not an increased CO₂, uptake per unit area, carbon,chlorophyll or dry weight, all of which either remained constantor decreased. Nitrate reductase activity was substantial inplants given nitrate but negligible in plants given urea. Neitherfree nitrate nor free urea contributed greatly to nitrogen levelsin plant tissues. It is concluded that there is no evidence for a restrictionin nitrate reduction at 6 C, and it is likely that urea givesgreater growth than nitrate because of greater rates of uptake. Vicia faba, broad bean, low temperature growth, carbon assimilation, nitrogen assimilation     

Dynamics of Carbon Photosynthetically Assimilated in Nodulated Soya Bean Plants under Steady-state Conditions 1. Development and Application of 13CO2 Assimilation System at a Constant 13C Abundance

A long-term, steady-state ¹³CO₂ assimilation system at a constantCO₂ concentration with a constant ¹³C abundance was designedand applied to quantitative investigations on the allocationof photoassimilated carbon in nodulated soya bean (Glycine maxL.) plants. The CO₂ concentration in the assimilation chamberand its ¹³C abundance were maintained constant with relativevariances of less than ±0.5 per cent during an 8-h assimilationperiod. At the termination of 8-h ¹³CO₂ assimilation by plantsat early flowering stage, the currently assimilated carbon relativeto total tissue carbon (measured by the degree of isotopic saturation)were for young leaves (including flower buds), 13.9 per cent;mature leaves, 15.7 per cent; stems+petioles, 5.9 per cent;roots, 5.4 per cent and nodules, 6.9 per cent, 48 h after theend of the ¹³CO₂ assimilation period, they were 12.3, 7.5, 7.4,6.8 and 6.1 per cent, respectively. The treatment with a highconcentration of nitrate in the nutrient media significantlydecreased the allocation of ¹³C into nodules. Experiments on¹³CO₂ assimilation by plants at the pod-filling stage were alsoconducted. Labelling by ¹³C was weaker than at the early floweringstage, but an intense accumulation of ¹³C into reproductiveorgans was observed. Glycine max L., nodulated soya bean plants, ¹³CO₂ assimilation, carbon dynamics     

Release of Guttation Fluid from Passive Hydathodes of Intact Barley Plants. II. The Effects of Abscisic Acid and Cytokinins

Guttation was used as a non-destructive way to study the flowof water and mineral ions from the roots and compared with parallelmeasurements of root exudation. Guttation of the leaves of barley seedlings depends on age andon the culture solution. Best rates of guttation were obtainedwith the primary leaves of 6- to 7-day-old seedlings grown onfull mineral nutrient solution. The growing leaf tissue becomessaturated with K⁺ below 1.5 mM K⁺ in the medium, whereas K⁺concentration in the guttated fluid still increases furtheras K⁺ concentration in the medium is raised. At 3 mM K⁺ averagevalues of guttation were 1.4–2.4 mm³ h^–1 per plantwith a K⁺ concentration of 10–20 mM; for exuding plantsthe flow was 4.2–7.6 mm³ h^–1 per plant and K⁺ concentration35–55 mM. Abscisic acid (ABA) at 10^–6 to 10^–4 M 0–2h after addition to the root medium increased volume flow ofguttation and exudation and the amount of K⁺ exported. Threeh after addition of ABA both volume and amount of K⁺ were reduced.There was an ABA-dependent increase in water permeability (Lp)of exuding roots shortly after ABA addition. Later Lp was decreasedby 35 per cent and salt export by 60 per cent suggesting aneffect of ABA on salt transport to the xylem apart from itseffect on Lp. Benzyladenine (5 x 10^–8 to 10^–5 M)and kinetin (5 x 10^–6 M) progressively reduced volumeflow and K⁺ export in guttation and exudation and reduced Lp. Guttation showed a qualitatively similar response to phytohormonesas found here and elsewhere using exuding roots. Hordeum vulgare L., barley, guttation, abscisic acid, cytokinins, benzyl adenine, kinetin     

Seasonal Changes in the Physiology of S24 Perennial Ryegrass (Lolium perenne L.). 1. Response of Leaf Extension to Temperature during the Transition from Vegetative to Reproductive Growth

The potential for leaf extension of plants of Lolium perennecv S24 growing in small artificial communities under naturalconditions was measured as the plants progressed from the vegetativeto the reproductive state In two consecutive years, 1975 and 1976, ‘simulated swards’were sown in autumn and overwintered in an open, unheated glasshouseIndividual swards from the batch sown in 1975 were brought into a growth room on two occasions in spring 1976 to measuretheir potential for leaf extension at a range of temperatures(5–20 °C) Individual swards from the batch sown inautumn 1976 were brought in to the growth room on 15 occasionsbetween November 1976 and May 1977 and their potential for leafextension was measured at a single temperature of 15 °CFrequent dissections were made in both years to describe changesin the developing apex. The potential for leaf extension at 15 °C decreased fromc 17 mm day^–1 in November to c 10 mm day^–1 in mid-winter.In January, the potential rapidly increased threefold to reach30mm day^–1 by mid February The increase began coincidentwith the earliest stages of floral initiation and was completedby the time of double-ridge formation Spring-grown vegetativeplants, however, showed potential rates of < 20 mm day^–1at 15 °C The results are discussed in relation to reproductive developmentand to changes in the carbohydrate strategy of the plants inearly spring Lolium perenne L perennial ryegrass, leaf extension, temperature response     

A Large-scale Isolation Procedure for Cereal Mesophyll Protoplasts

A method suitable for the large-scale isolation of cereal protoplastsfrom up to 50 g of leaf material is described. Surface-sterilizedleaves from cultivars of wheat, barley, maize, sorghum, andTriticale were diced and vacuum infiltrated with enzyme mixturecomposed of cellulysin (1 per cent w/v), hemicellulase (1 percent w/v), and macerozyme (0.5 per cent w/v). With this procedure,yields of between 10⁶ to 10⁷ protoplasts per gram of leavescan be reproducibly obtained after only 1.5–3 h of enzymatictreatment. These protoplasts were almost 100 per cent viable(as determined by fluorescein diacetate staining) and incorporationof ³H-uridine and ¹⁴C-leucine into an acid-insoluble fractionwas demonstrated. Almost one-third of the ribosomes of theseisolated protoplasts were present as polysomes. cereals, leaf mesophyll, protoplast isolation     

The Occurrence of Nitrate Reduction in the Leaves of Woody Plants

Nitrate reductase activities greater than 02 µmol h^–1g^–1 f. wt, measured by an in vivo assay, occurred in 41per cent of a large sample (555 species) of woody plants. Ifseveral taxonomic groups (Gymnosperms, Ericaceae and Proteaceae)with consistently low activities were discounted activitiesgreater than 02 µmol h^–1 g^–1 f. wt occurredin 73 per cent of the species. This compares with 93 per centin herbaceous species, suggesting that leaf nitrate reductionis of common occurrence in woody plants. In a small sample ofspecies leaf nitrate reductase activity correlated with nitrateconcentration in the xylem sap. Low activities occurred consistentlyin the Gymnosperms, Ericaceae and Proteaceae. Feeding cut shootsof representatives of these groups with nitrate caused inductionof leaf nitrate reductase activity in the Gymnosperms and Proteaceae,but only limited induction in the Ericaceae. The Ericaceae,with the exception of two species, had low activities and lownitrate reductase inducibility. Root assimilation may predominatein the Gymnosperms and Proteaceae. It is suggested that nitratereduction generally occurs in the leaves of trees from a varietyof plant communities and that this may be related to the lowerenergy cost of leaf, as opposed to root, nitrate assimilation. Nitrate reductase, trees and shrubs, leaves, nitrate assimilation, nitrate translocation, nitrate reductase induction, energy cost, plant ecology     

Variations with Age in Net Assimilation Rate and other Growth Attributes of Sugar-beet, Potato, and Barley in a Controlled Environment: With two Figures in the Text

Sugar-beet, potato, and barley plants were grown in a controlledenvironment, for periods of up to 10 weeks from sowing, witha light intensity of 1,8oo f.c. (4·9 cal./cm.²/hr.) anda temperature of 20° C. during the 18-hour photoperiod and15° C. during the dark period, to test whether net assimilationrate varied with age and differed between the three species. Net assimilation rate of all species based on leaf area (E_A)fell approximately linearly with time. During 5 weeks E_A ofsugar-beet decreased by only about 20 per cent. and E_A of potatodecreased by 50 per cent. E_A of barley remained approximatelyconstant for 4 weeks after sowing and was halved during thesubsequent 4 weeks. The average value of E_A for all times wasgreatest for sugarbeet and least for barley. Net assimilation rates based on leaf weight (E_W) and leaf N(E_N) decreased at about 15 per cent. of the initial value perweek for all species; this was similar to the mean rate of decreaseof E_A of potato and barley, but greater than that of E_A of sugar-beet.Mean values of E_W or E_N for potato and barley were similar andless than for sugar-beet. Relative growth rate (R_W), relative leaf growth-rate (R_A), andleaf-area ratio (F) fell with time at similar rates for allspecies. Average values of R_W decreased and of F increased inthe order sugar-beet, potato, barley. R_A was greatest for potatoand least for barley.