Synthesis of Citrulline and Arginine in Chlorella pyrenoidosa

The distribution of radioactivity in Chlorella during dark ¹⁴CO₂fixation was investigated either (a) in normal cells with andwithout added ammonium chloride, or (b) in nitrogen-starvedcells supplied with intermediates of the Krebs-Henseleit ureacycle. In the control experiments almost all the activity was presentin compounds of or associated with, the tricarboxylic acid cycle. The amino-acids citrulline and arginine became radioactive onlyin the presence of ammonia or ornithine where initially theycomprised 40–60 per cent. of the total activity, reactionsof the Krebs–Henseleit urea cycle being implicated intheir formation. No evidence could be found for a complete ureacycle. Unidentified compounds deriving their radioactivity fromthe C₄ carbon of citrulline and/or arginine were detected andformed up to 40 per cent. of the total ¹⁴CO₂ incorporated after25 min.     

The Oxidation of 14C-labelled Glucose by Chlorella vulgaris: 2. The Fate of Radioactive Carbon

Most of the ¹⁴C added as glucose to carbohydrate-starved cellsof Chlorella Vulgaris can be recovered as alcohol-soluble compoundsor as polysaccharide. Only 5–I6 per cent., depending onthe position of ¹⁴C in the glucose supplied, is released ascarbon dioxide. Similar results were obtained with Chlorellapyrenoidosa and Ankistrodesmus. The labelled alcohol-solublecompounds in Chlorella vulgaris include amino-acids, particularlyglutamic acid, aspartic acid, and alanine, and, when glucose-I-¹⁴Cis metabolized, the amount of ¹⁴C recovered in these amino-acidsis about the same as that recovered as carbon dioxide. Degradationof the glucose incorporated into polysaccharide shown that theC₁ and C₆ atoms of glucose rapidly interchange when in the cells.The bearing of these results on attempts to estimate the relativeimportance of different pathways of glucose breakdown is discussed.     

Photosynthesizing Leaves and Nodulated Roots as Donors of Carbon to Protein of the Shoot of the Field Pea (Pisum arvense L.)

In Pisum arvense, the amides and amino-acids normally suppliedto the shoot in the transpiration stream transfer carbon toprotein largely throught the amino-acids, aspartic acid (+asparagine),glutarnic acid (+glutamine), threonine, lysine, arginine, andproline. Carbon from carbon dioxide enters the protein of photosynthesizingtissues through an essentially complementary set of amino-acidsincluding glycine, alanine, serine, valine, and the aromaticamino-acids tyrosine, phenylalnine, and histidine. Young tissuesof the shoot synthesize certain amino-acids de novo by metabolismof sugars supplied from photosynthesizing leaves. Each mature leaf on a shoot contributes carbon to current synthesisof protein at the shoot apex. Sucrose accounts for more than90 per cent of the labelled carbon leaving any age of leaf whichhas been fed with ¹⁴CO₂. Upper leaves supply labelled assimilatesdirectly to the shoot apex, and the radiocarbon from these assimilatesis subsequently incorporated into a wide range of amino-acidunits of protein. The majority of the labelled assimilates exportedfrom a lower leaf move downwards to the root and nodules and,in consequence, the amino-acids and amides associated with rootmetabolism are strongly represented among the compounds eventuallylabelled in the apical region of the shoot.     

Nutritional Factors Influencing the Production of Sclerotia by Certain Fungi

In various fungi (Botrytis cinerea, B. allii, Sclerotinia gladioli,Sclerotiun cepivorum, S. rolfsii, and Rhizoctonia solani) theinitiation of sclerotia, their further development to full sizeand their maturation were three distinct stages with differentnutritional requirements. These processes were followed on peptone-saltsmedia with a variety of carbon sources (carbohydrate or mannitol)ranging in concentration between 0·5 and 3 per cent.The nitrogen nutrition was varied in the presence of 2 per cent.glucose with peptone replaced by asparagine, potassium nitrate,or ammonium salts. All were suitable provided a high aciditydid not develop. Urea was unsatisfactory. Details given includethe rate of sugar utilization in some examples.     

Secondary Sporangium Formation in Phytophthora Palmivora (Butl.) Butl

Very few sporangia of Phytophthora palmivora germinated directlyand produced secondary sporangia in distilled water and in solutionsof amino acids and carbohydrates at 30 °C. Although 1.0per cent (w / v) peptone and yeast-extract stimulated a highpercentage of germination by formation of germ tubes, less than1.0 per cent of the germinated sporangia produced secondarysporangia. Secondary sporangium formation was induced by transferringgerminated primary sporangia from a nutrient medium of sufficientlyhigh concentration to either distilled water or dilute solutionsof organic and inorganic compounds immediately after emergenceof the germ tubes. The percentage of germinated sporangia formingsecondary sporangia was influenced by both the nature and concentrationof the medium into which they were transferred. The secondarysporangia were significantly smaller than the primary sporangia. Phytophthora palmivora, germination, sporangium, Theobroma cacao L., cocoa     

Contributions to Grain Yield from Pre-anthesis Assimilation in Tall and Dwarf Barley Phenotypes in Two Contrasting Seasons

Twenty-four barley genotypes were produced from crosses betweentwo sets of parents each having a different, non-allelic dwarfinggene. Four genotypes were phenotypically tall, twelve were singledwarf and eight were double dwarf. By a combination of carbon-14labelling and growth measurement the contribution to grain drymatter from assimilation before anthesis was estimated for eachgenotype in two years, 1976 and 1977. Pre-anthesis assimilation was estimated to have contributed44 per cent of grain dry matter in 1976, a very dry, hot year,but only 11 per cent in 1977, a wetter, cooler year. These percentageswere equivalent to about 133 and 74 g m^–2 in 1976 and1977. It is shown that some previous estimates of the contributionfrom pre-anthesis assimilation are too low for crops of barleygrown in the field in dry years, while in wet years, the contributionis unlikely to be less than 10 per cent. In neither year did the genotypes differ in the extent to whichpre-anthesis assimilation contributed to grain filling. In bothyears, grain yields of the tall genotypes were 8–9 percent greater than those of the double dwarf ones, and stem weightsat maturity 30 per cent greater. Hordeum vulgare L., barley, grain yield, carbon assimilation     

Dry Matter Yields and Photosynthetic Rates of Diploid and Hexaploid Triticum Species

The above ground dry matter yields of two wild diploid Triticumspecies averaged 76 per cent of that of two hexaploid breadwheat varieties in field trials carried out over five years.A cultivated diploid species, T. monococcum, gave similar drymatter yields to the bread wheat varieties but had a longergrowth cycle. The flag leaves of wild diploid species had higher rates ofphotosynthesis than those of the bread wheat varieties bothwhen expressed per unit area of leaf or per unit weight of chlorophyll.Photosynthetic rates of other organs, expressed per unit weightof chlorophyll were also greater for the wild diploids thanfor hexaploids. For snoots at the stage when their flag leaveswere fully expanded, the investment in photosynthetic machinery,as measured by chlorophyll concentration, was less in the twowild diploids than in the hexaploids. This compensated for thehigh photosynthetic rate of the former, such that the specificgrowth rates, assessed by carbon-14 fixation per unit shootdry matter, were similar. Triticum spp., wheat, dry matter yield, photosynthesis, carbon-14, ploidy     

Carbon Translocation in the Tomato: Pathways of Carbon Metabolism in the Fruit-

The rate of carbon import by tomato fruits has been relatedto their carbon metabolism by examining the effects of fruittemperature on the metabolism of imported assimilates. ¹⁴C–sucrose,–glucose, –fructose, –malic acid and –citricacid were injected individually into young growing tomato fruitswhich were subsequently maintained at 25 or 5 °C for 48h. Fruit temperature greatly affected the proportions of ¹⁴Clost from the fruits by export and respiration. Only 40 percent of the injected ¹⁴C from ¹⁴C–sugars and 20 per centfrom ¹⁴C–acids was recovered from fruits at 25 °C.Less than 10 per cent of the injected ¹⁴C was exported, thebalance being respired. In contrast, more than 50 per cent ofthe injected ¹⁴C was recovered from cooled fruits, in whichthe import rate of carbon was presumably reduced, and 20–36per cent of injected ¹⁴C was exported. Cooling enhanced thesynthesis of ¹⁴C–sucrose from injected ¹⁴C–hexosesand inhibited the incorporation of ¹⁴C into starch and insolubleresidue. When ¹⁴C–sugars were injected, radioactivityexported from the cooled fruits was detected as sucrose in thephloem of the peduncles; radioactivity was also detected instems and roots when fruits were cooled. In almost fully–grownfruits injected ¹⁴C–compounds were metabolized less readilythan in smaller fruits. Conversion of ¹⁴C–hexoses to ¹⁴C–sucrosewas again enhanced by cooling (5 °C, but was less in fruitsmaintained at 35 °C than in controls. Lycopersicon esculentum, tomato, fruit, translocation, carbon metabolism     

Links between Glucose Uptake and Metabolism in Nitella translucens

The uptake of ¹⁴C-glucose into cells of Nitella translucenshas been investigated under experimental conditions previouslyused in studies of the ionic relations of these cells. Glucoseentry was considerably stimulated by light, and under aerobicconditions the fluxes remained constant for many hours. Theinflux of glucose was inhibited by over 80 per cent at low temperature(4° C) and by over 90 per cent by the uncoupler carbonylcycanide-m-chlorophenylhydrazone. 2-Deoxy-D-glucose was a non-competitiveinhibitor of glucose uptake both in light and darkness. Cyclicphotophosphorylation promoted the influx (with decreasing efficiency)for several hours. It is suggested that an ATP-dependent transportprocess controls glucose entry to the cells, and that passivediffusion is of little significance.     

Germination of Talinum triangulare L. Seeds as Affected by Various Chemical and Physical Treatments

Three-month ‘old’ and ‘fresh’ seedsof Talinum triangulare were subjected to various treatmentsto induce early and rapid germination. Scarification and activated carbon were the most effective treatmentsin improving total germination in fresh seeds, while the 3 and5 per cent thiourea treatments were most effective in improvingtotal germination in old seeds. Activated carbon, scarificationand 5 per cent thiourea treatments enhanced early germinationin both old and fresh seeds. Cumulative percentage germinationwas very high in fresh seeds after scarification or after treatmentwith activated carbon and 5 per cent thiourea, and lowest inseeds treated with 3 per cent thiourea and hot water. In oldseeds, highest cumulative percentage germination was obtainedwith 3 and 5 per cent thiourea treatments and scarification.Generally, higher germination was obtained with fresh seedsthan with old seeds. Partial seed-coat removal and treatment with 5 per cent thiouriaresulted in a higher rate of and cumulative percentage germinationcompared with seeds with the coat partially removed but nottreated with thiourea. Constantly high temperature (34 °C) increased both rateand total germination compared with seeds planted at room temperature(20–23 °C). Treatments that did not induce germinationwere 1 per cent thiourea, H₂SO₄, cold water soaking at roomtemperature, 6 per cent hydrogen peroxide and soil planting.These treatments effected less than 3 per cent germination. Talinum triangulare L, seed scarification, activated charcoal, thiourea, germination     

EFFECTS OF CHLORAMPHENICOL AND KINETIN ON UPTAKE AND INCORPORATION OF AMINO ACIDS BY TOBACCO LEAF DISKS

The effects of chloramphenicol and kinetin on uptake and incorporationof ³⁵S-methionine and some ₁₄C-amino acids have been investigatedin leaf-disks of Nicotiana rustica in light and dark. Chloramphenicolin a concentration of 1 mg per ml inhibits the uptake of aminoacids from 30 to 60 per cent compared with the water control.The incorporation of amino acids into bulk protein is stronglyinhibited in light (40 to 70 per cent), but only to a smalldegree in dark (10 to 20 per cent), as revealed also by ¹⁴CO₂-photosynthesisof the disks and following treatment with chloramphenicol indark. The stimulating effect of kinetin on uptake and incorporationof amino acids is dependent upon its concentration (10^–5to 10^–6 M ; but 10^–4 M solution inhibits stronglyboth uptake and incorporation). The stimulation seems to influencemore incorporation than uptake processes. Possible interactionsof chloramphenicol and kinetin in the protein metabolism oftobacco leaves have been discussed. (Received April 27, 1964; )     

The Uptake of Growth Substances: X. THE ACCUMULATION OF PHENOXYACETIC ACID AND 2,4-DICHLOROPHENOXYACETIC ACID BY SEGMENTS OF AVENA MESOCOTYL

Segments of Avena mesocotyl were placed in buffered solutionsof phenoxyacetic acid (POA) or 2,4-dichlorophebnoxyacetic acid(2,4-D), containing carbon-14 in the carboxyl group, and thequantities of radioactivity taken up by the tissues measured.With freshly cut segments in solutions of 2,4-D there is accumulationof carbon-14, but the course of uptake is interrupted by a temporaryphase when some of the accumulated 2,4-D is released to theexternal solution. If after cutting the segments are first pretreatedby placing them for about 15 h in buffer, and then transferredto 2,4-D, there is progressive accumulation with no phase ofnet loss. Pretreated segments absorb greater quantities of either 2,4-Dor POA than freshly excised tissues. Following pretreatmentin buffer the course of uptake of POA is linear but for 2,4-Dthe course is curvilinear. However, after pretreatment withnon-radioactive 2,4-D the subsequent rate of uptake of radioactive2,4-D is constant over long periods. The uptake of radioactive2,4-D is largely independent of the concentration of non-radioactive2,4-D given during pretreatment. When segments which have absorbed 2,4-D-1-¹⁴C are transferredto buffer, a relatively small proportion of the carbon-14, the‘mobile fraction’, is released. The amount releasedfollowing different periods of uptake is constant whereas thelevel of non-mobile carbon-14, the ‘residual fraction’,rises progressively in step with accumulation. The uptake of POA and 2,4-D is accompained by the formationwithin the tissues of other radioactive substances. It is concludedthat the residual fraction is composed, at least in part, ofthese metabolic products and that accumulation and metabolicconversion are inter-connected. Dinitrophenol (DNP) slowly and progressively depresses the uptakeof POA whereas the uptake of 2,4-D is very rapidly arrested.However, after about 2 h, in the continued presence of DNP,uptake of 2,4-D restarts but the rate never attains that ofthe control. These divergent effects of DNP indicate that POAand 2,4-D are accumulated by different pathways.     

Thermal and Water Relations of Roots of Desert Succulents

Two succulent perennials from the Sonoran Desert, Agave desertiEngelm. and Ferocactus acanthodes (Lem.) Britton and Rose, loselittle water through their roots during drought, yet respondrapidly to light rainfall. Their roots tend to be shallow, althoughabsent from the upper 20 mm or so of the soil. During 12–15d after a rainfall, new root production increased total rootlength by 47 per cent to 740 m for A. deserti and by 27 percent to 230 m for F. acanthodes; root dry weight then averagedonly 15 per cent of shoot dry weight. The annual carbon allocatedto dry weight of new roots required 11 per cent of shoot carbondioxide uptake for A. deserti and 19 per cent for F. acanthodes.Elongation of new roots was greatest near a soil temperatureof 30°C, and lethal temperature extremes (causing a 50 percent decrease in root parenchyma cells taking up stain) were56°C and -7°C. Soil temperatures annually exceeded themeasured tolerance to high temperature at depths less than 20mm, probably explaining the lack of roots in this zone. Attached roots immersed in solutions with osmotic potentialsabove -2·6 MPa could produce new lateral roots, with50 per cent of maximum elongation occurring near -1·4MPa for both species. Non-droughted roots lost water when immersedin solutions with osmotic potentials below -0·8 MPa,and root hydraulic conductance decreased markedly below about-1·2 MPa. Pressure-volume curves indicated that, fora given change in water potential, non-droughted roots lostthree to five times more water than droughted roots, non-droughtedleaves, or non-droughted stems. Hence, such roots, which couldbe produced in response to a rainfall, will lose the most tissuewater with the onset of drought, the resulting shrinkage beingaccompanied by reduced root hydraulic conductance, less contactwith drying soil, and less water loss from the plant to thesoil. Agave deserti, Ferocactus acanthodes, roots, soil, temperature, water stress, drought, Crassulacean acid metabolism, succulents     

Minerals, Carbohydrates and Amino Acids of Pollens from some Woody and Herbaceous Plants

The mineral, carbohydrate, protein, amino acid, lipid and energycontents of the seven main pollens gathered by honey-bees insouth-east Scotland were determined. Neither dry matter (mean73 per cent) nor ash (mean 3 per cent) were very variable. Thecalcium content of all pollens was relatively similar as werethe magnesium, potassium and sodium contents but manganese whichwas relatively high in ericaceae and phosphorus which was lowin Trifolium were more variable. Acer pollen contained mostprotein and Fagus least, and of the amino acids only serine,cystine and histidine were significantly different in the differentpollens. Over 30 per cent of all pollens was a mixture of fructoseand glucose, ericaceae containing most and Acer least. Hemicellulose(mean 7 per cent) was high in Ranunculus and low in Acer, cruciferaeand Fagus. ‘Cellulose’ (mean 0•5 per cent)was high in cruciferae and low in ericacea. Ether extract (mean5 per cent) was high in cruciferae and Fagus. The mean grossenergy of pollen was 23 kJ g^–1. Fresh pollen is comparable with lean meat as a source of energyand protein, and is more like dormant plant seeds than herbagein its water, ash and protein content but stores energy as sugarrather than starch or lipid.     

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     

Coefficients of distribution of cyclic polyether macrotetrolide antibiotics between hydrophobic and hydrophilic solvents

Dependence of distribution of 14C-macrotetrolide antibiotics between water and chloroform on the presence of various additives in the aqueous phase was studied with the radioindicator procedure. It was shown that in comparison to distilled water aqueous solutions of chlorine salts of ammonium, potassium and sodium increased the content of macrotetrolides in chloroform as a result of forming strong hydrophobic complexes. This is especially applied to the ions of ammonium whose addition to the aqueous phase led to an increase of macrotetrolide level in chloroform up to 98.4 per cent. Addition of weak hydrochloric acid or alkaline agents resulted in marked transfer of the ionophores into the aqueous phase at the expense of hydrolysis of the antibiotic cyclic molecules. The highest hydrolysis levels were induced by potassium hydroxide, the content of the ionophores in the hydrophobic phase decreasing up to 90.6 per cent. The effect of picric acid on distribution of the macrotetrolides between water and chloroform was different and depended on its concentration.     

Overcoming Incompatibility in Brassica campestris L. by Carbon Dioxide, and Dark Fixation of the Gas by Self- and Cross-pollinated Pistils

Supplementing pollen suspension cultures with CO₂ (3–5per cent) caused a marked increase in germination and tube growthin vitro in Brassica campestris L. cv. toria. A weakening ofself-incompatibility by increased CO₂ levels from 3–5per cent was observed. The percentage of pollen tubes whichpenetrated the cuticle layer of stigmatic papilla cells in self-pollinatedpistils was high when CO₂ level was 5 per cent. Phosphoenolpyruvate (PEP) carboxylase activity was greater in the pollengerminated in 4 per cent CO₂ as compared to air (0.03 per cent).A possible role of CO₂ for self-recognition and control of pollentube growth is proposed, proposed. Brassica campestris L., carbon dioxide, self-incompatibility, phosphoenol pyruvate carboxylase     

Further Observations on Root--Shoot Equilibria in Perennial Ryegrass (Lolium perenne L.)

Plants of Lolium perenne L. (cv. S. 23) were grown in a heatedglasshouse. Two experiments were performed, both during earlysummer. One used a sand/solution rooting medium and includedlow-nitrogen (0.17 parts per 10⁶) and shade (20.2 per cent illumination)treatments; the other used aerated solution culture and involvedtwo levels of shading (20.2 and 6.1 per cent illumination),in addition to controls. In both experiments growth and ratesof potassium, magnesium and calcium uptake were studied throughthe calculation of various growth-functions from fitted curves. Despite the effects of treatment and environment, a constantinverse relationship was found between the mass ratio of rootsand shoots and their activity ratio. These new results wereadded to some previously published to form a combined model:mass ratio = 0.051 + 45.7 (1/activity ratio) where activityratio is expressed as specific absorption rate for potassium(in µg K mg root^–1 day^–1)/unit shoot rate(rate of increase of whole-plant dry weight per unit shoot weight,mg mg^–1 day^–1). The implications of this relationshipare discussed and a further model is put forward in which rootactivity is expressed in terms of the uptake of the sum of thepotassium, magnesium and calcium contents of the plant.     

A Two-dimensional Model for Water Uptake by Desert Succulents: Implications of Root Distribution

Water uptake by Agave deserti and Ferocatus acanthodes was predictedusing a two-dimensional simulation model in which the soil arounda plant was divided into a series of layers and concentric cylindricalshells. Root lengths in 0.05 m thick soil layers were determinedfor both species in the field, where mean root depths were only0.11 m for A. deserti and 0.10 m for F. acanthodes. For a yearwith average precipitation (159 mm), 42 per cent of the annualprecipitation could be taken up by A. deserti and 25 per centby F. acanthodes. Predicted water uptake by both species wasgreater from the upper soil layers (above 0.15 m) for averageand dry years, but was greater from the deeper layers for awet year. The actual root distribution for both species ledto more water uptake than when all of the roots were in a singlelayer. The large number of days per year when the soil temperaturesexceeded 57 °C (the temperature for 50 per cent inhibitionof uptake of a vital stain by root cells) may exclude rootsfrom the 0.00–0.05 m soil layer, even though water uptakewhen all roots were located there was predicted to be maximal.Therefore, the observed root distribution of A. deserti andF. acanthodes may be limited near the soil surface by high temperaturesand at maximum depths by water availability for all but wetyears. Agave deserti, Ferocactus acanthodes, desert succulents, root system, root distribution, soil temperature, water uptake     

The Function of the Hilum in Some Papilionaceae in Relation to the Ripening of the Seed and the Permeability of the Testa

In seeds of Trifolium repens, T. pratense, and Lupinus arboreus,the hilum is a hygroscopically activated valve in the impermeableepidermis of the testa. When relative humidity was low the fissurein the hilum opened permitting the seed to dry out; when therelative humidity was high the fissure closed obstructing theabsorption of moisture. During seed-ripening the moisture contentfell readily to approximately 25 per cent., and thereafter moreslowly until the epidermis became impermeable at approximately14 per cent, moisture content. Further drying of the seed tookplace only by diffusion of water vapour through the hilum. ‘Hard’seeds tended to have a moisture content in equilibrium withthe lowest relative humidity to which they had been exposed.They absorbed moisture under conditions of gradually increasingrelative humidity such that the hilar fissure remained open.The duration of the impermeable condition increased with thedegree of desiccation brought about by loss of water throughthe hilum.