Carbon Dioxide Fixation by Barley Roots

The non-volatile, 80 per cent.ethanol-soluble products of fixationhave been investigated in excised roots, using C^14O₂ and radiochromatography. The main radioactive compounds separated were malic, citric(or iso-citric), aspartic, and glutamic acids, asparagine andglutamine. Less activity was present in serine, tyrosine, -ketoglutaricacid, and alanine, and in a number of unidentified compounds. The uptake of C^14O₂ was inhibited by virtually anaerobic conditions. From the above observations it is considered likely that C¹⁴is transformed through the reactions of the tricarboxylic acidcycle. C¹⁴ in the soluble fraction was markedly increased by maintainingthe root material in water rather than in a nutrient solutionprior to exposure to C^14O₂ This increase was chiefly in malicacid.     

A Transient Stimulation of Net Photosynthesis of Rye Leaves by {alpha}-Hydroxy-2-pyridinemethanesulphonic Acid ({alpha}-HPMS) due to Inhibition of Photorespiratory CO2 Release

The effects of -hydroxy-2-pyridinemethanesulphonic acid (-HPMS)upon net photosynthesis (P_n, the CO₂ compensation point (),post-lower illumination burst of CO₂ (PLIB) and post-lower temperatureburst of CO₂ (PLTB) in detached rye (Secale cereale L.) leaveswere investigated. At low concentrations ( 0.5 mol m^–3),-HPMS initially stimulated P_n and decreased the magnitude ofboth PLIB and PLTB. The decreased at all concentrations of-HPMS (0.05–5.0 mol m^–3. The effects of -HPMS onP_n and were time-dependent and, after a few minutes, the P_nwas inhibited while values increased considerably. At a higherconcentration (5.0 mol m ^–3), the transient effects of-HPMS were shorter () or not observed at all (P_n. Both PLIBand PLTB, when expressed in relation to P_n, increased at higherlevels of this compound. Similar data with respect to the effectsof -HPMS on PLIB and PLTB were found for leaves of dandelion(Taraxacum officinale L.). The results suggest that -HPMS may stimulate P_n by inhibitingphotorespiration, as originally suggested by Zelitch (1966),but only at low concentrations and over a short time span. Thedecrease of PLIB and PLTB values at low -HPMS levels is consistentwith these processes being a residual activity of the glycolatepathway. Key words: CO₂ compensation point, -hydroxy-2-pyridinemethanesulphonic acid, photorespiration, photosynthesis     

The Effect of Hydroxymethanesulphonate on Photosynthesis in Chlorella pyrenoidosa

Photosynthesis under conditions known to favour glycollate excretionby algae did not result in glycollate excretion in a strainof Chlorella pyrenoidosa unless an inhibitor of glycollate oxidase,-hydroxypyridin-2yl-methane sulphonate (-HPMS), was present.This inhibitor increased the total amount of glycollate presentin the supernatant from the cells during photosynthetic carbondioxide fixation and gave accumulation of ¹⁴C in glycollateduring ¹⁴CO₂ fixation under conditions favouring glycollatesynthesis. At pH 8.3 -HPMS did not stimulate photosynthetic¹⁴CO₂ fixation in C. pyrenoidosa as occurs with some algae.Photoassimilation of acetate was inhibited by -HPMS, and thiswas shown to result from acetyl-CoA synthetase inhibition by-HPMS.     

{alpha}-Amylase Production by Pre-mature Wheat (Triticum aestivum L.) Embryos

Embryo/scutellar tissue of pre-mature wheat grains usually containslittle -amylase but readily produces the enzyme upon removalfrom the caryopsis. Enzyme production is accompanied by cytologicalchanges in the scutellar epithelium cells characteristic ofgerminating mature embryos, although -amylase production bypre-mature tissue is not always associated with germinativegrowth of the embryonic axis. Production of -amylase is influencedby embryo age, stimulated by GA₃ and overall is inhibited byABA. Examination by isoelectric focussing and rocket-line immuno-electrophoresisreveals the presence of both -AMYl and -AMY2 isoenzymes, thelatter being the major constituent. In the presence of ABA certain-AMY2 isoenzymes not detected previously are observed. Key words: a-Amylase, wheat, embryo     

The Derivation of the Cell Wall Elasticity Function from the Cell Turgor Potential

An equation is derived expressing average turgor pressure ofa leaf (_p) as a function of relative water content (RWC). Basedon this derivation, the relationships of the bulk elastic modulus(_v) and both RWC and _p, are formulated and discussed. The bulkelastic modulus (_v) becomes zero for _p = 0, that is at the turgorloss point for the leaf. At full water saturation the valueof ev is proportional to the water saturation turgor potential_p(max). The factor relating _P and _v (structure coefficient ,Burstrom, Uhrstr?m and Olausson, 1970) changes only very littlefor values of _p, which are not too close to zero. An exampleis given for the calculation from experimental data of the turgorpressure function, the structure coefficient function, and the_v function. Key words: Cell wall, Turgor pressure, Bulk elastic modulus     

An Analysis of Some Effects of Humidity on Photosynthesis by a Tomato Canopy under Winter Light Conditions and a Range of Carbon Dioxide Concentrations

The rates of net photosynthesis by closed canopies of tomatoplants were measured at three CO₂ concentrations and three humiditiesover a range of natural light flux densities. The data havebeen analysed using a model of canopy photosynthesis which allowsfor variation in leaf area index and other leaf and canopy characteristics.The model also deals explicitly with the effects of CO₂ concentration,leaf conductance, and photorespiration on the leaf photochemicalefficiency, . The leaves were found to have a photochemicalefficiency in the absence of photorespiration, _m, of 12?6 ?10^–9 kg (CO₂) J^–1. At a CO₂ concentration of 0?73 ? 10^–3 kg m^–3 (400vpm) the leaf photochemical efficiency, , and canopy light utilizationefficiency, _c, were 18 per cent greater at a vapour pressuredeficit of 0?5 kPa than at 1?0 kPa. At a CO₂ concentration of2?2 ? 10^–3 kg m^–3 (1200 vpm) they were only 5 percent greater.     

An Assessment of Gibberellin Structure-activity Relationships

Information on the biological activities of gibberellins (GAs)in the barley aleurone, Tangin-bozu dwarf rice, dwarf pea, lettucehypocotyl and cucumber hypocotyl bioassays is reviewed and discussedin the context of GA structure-activity relationships. The barley aleurone bioassay exhibits a limited response toGAs and it is suggested that this may be because the aleuronecells are able to carry out few GA interconversions. Consequentlyactivity is determined by the degree of compatibility betweenthe GAs and a receptor site. In this assay high biological activityis associated with GAs having a 3ß-hydroxy--lactonestructure. This activity is substantially enhanced by the additionalpresence of a 13-hydroxyl group. The substitution of a -lactoneor a -lactol for a -lactone results in reduced activity while3ß,13-dihydroxy GAs with either 20-carboxyl or 20-methylfunctions are completely inactive. The Tanginbozu dwarf ricebioassay responds to many more GAs than the barley aleuronesystem possibly because the rice seedlings can carry out extensiveGA interconversions. Under these circumstances GAs that areinactive per se can be metabolically converted to active forms.There is no interaction between the 3ß- and 13-hydroxyfunctions of GA molecules in the rice assay. Activity appearsto be determined by the degree oxidation of the C-20 group.The order of activity is usually -lactone > -lactol >-lactone > methyl > carboxyl. It is suggested this mayindicate that in rice seedlings C₂₀-GAs are converted to C₁₉-GAsvia a Baeyer-Villiger type oxidation. Activity in the dwarfpea bioassay is dependent upon GAs possessing both 3ß-and 13-hydroxyl groups and is again related to the state ofoxidation at the C-20 locus. In the lettuce bioassay activityis restricted to GAs with a -lactone function. In some instancesa -lactone, but not a -lactol, can substitute effectively. Thismay imply that the applied C₂₀-GAs are not converted to C₁₉-GAsand that the response to the -lactone results from the six-memberedring mimicking the -lactone at the receptor site. Only GAs havinga 19,10 or a 19,20 lactonic bridge show substantial activityin the cucumber bioassay. The additional presence of eithera 12- or a 13-hydroxyl group severely reduces activity.     

Penicillin Induction of Gibberellin and {alpha}-Amylase Biosynthesis in Rice Endosperm

Penicillin induces the synthesis of -amylase in embryoless riceendosperm and enhances the gibberellin-induced response. Penicillininduction of -amylase can be prevented by inhibitors of nucleicacid and protein synthesis, CCC and 2,4-DNP. A characteristic gibberellin-like activity in the extracts frompenicillin-treated endosperms becomes detectable after 12 hfrom the addition of penicillin. This gibberellin-like activityis located on paper chromatograms at the R_F typical for GA₃and its formation is blocked by CCC, an inhibitor of GA biogenesis.Glucose has no effect on the biosynthesis of either gibberellinor -amylase induced by penicillin. The time-course study of the levels of different constituentsshows that penicillin probably induces RNA and DNA synthesisin the first place, which results in gibberellin biosynthesis,which in turn stimulates the synthesis of -amylase. The possiblemode of action of penicillin in higher plants is discussed.     

The Labelling of Malic and Citric Acids of Pea Leaves and Cotyledons of Germinating Peas by 14CO2 in the Dark

Leaflets of green pea plants and cotyledons of germinating peaswere kept in the dark in air containing ¹⁴CO₂. The malate extractedwas labelled to 35–40 per cent in the C-1 position andthe citric acid was labelled to 70–75 per cent in theC-6 position. This showed that two carboxylations, at least,were involved in both tissues, i.e. probably of a three-carbonacid to form malate, and of -oxoglutarate to form isocitrate.     

Alterations in the Components of Peanut Leaf Water Potential during Desiccation

Changes in components of leaf water potential during soil waterdeficits influence many physiological processes. Research resultsfocusing on these changes during desiccation of peanut (Arachishypogeae L.) leaves are apparently not available. The presentstudy was conducted to examine the relationships of leaf water_l, solute _s and turgor _p potentials, and percent relative watercontent (RWC) of peanut leaves during desiccation of detachedleaves and also during naturally occurring soil moisture deficitsin the field. The relationship of _p to _l and RWC was evaluated by calculating_p from differences in _l and _s determined by thermocouple psychrometryand by constructing pressure-volume (P-V) curves from the _land RWC measurements. Turgor potentials of ‘Early Bunch’and ‘Florunner’ leaves decreased to zero at _l of–1.2 to –1.3 MPa and RWC of 87%. There were no cultivardifferences in the _l at which _p became zero. P-V curves indicatedthat the error of measuring _s after freezing due to dilutionof the cellular constituents was small but resulted in artefactualnegative _p values. Random measurements on two dates of _l, _s, and calculation of_p from well-watered and water-stressed field plots consistingof several genotypes indicated that zero _p occurred at _l of–1.6 MPa. It was concluded that the relationships of _p,_l, _s, and RWC of peanut leaves were similar to leaves of othercrops and that these relationships conferred no unique droughtresistance mechanism to peanut.     

Glycosidases from Cotyledons of Pisum sativum L.

-Mannosidase and ß-N-acetylglucosaminidase were purifiedfrom extracts of cotyledons of germinating Pisum sativum L.A 13-fold purification of a-mannosidase free from ß-N-acetylglucosaminidaseactivity was achieved by precipitation in ammonium sulphate,column chromatography on DEAE-cellulose, and treatment with2 M pyridine. ß-N-Acetylglucosaminidase was purified200-fold by the use of (NH₄)₂SO₄, and chromatography on ConcanavalinA¹-Sepharose and Sephacryl-200. This preparation showed no measurablecontamination by -mannosidase activity. Both glycosidases appearto be glycoproteins and demonstrate optimal activity at pH valuesof 4.0–4.5. Both glycosidases appear to have very similarmolecular weights, with -mannosidase being slightly larger thanß-N-acetylglucosaminidase. An extensive search forthe activity of aspartylglycosylamine amido hydrolase in peacotyledons proved unsuccessful.     

Uptake and Accumulation of {alpha}-Naphthalene Acetic Acid by Cell Suspensions of Galium mollugo L.

Fidgeon, C. and Wilson, G. 1988. Uptake and accumulation ofa-naphthalene acetic acid by cell suspensions of Galium mollugoL.—J. exp. Bot. 39: 241-249. Galium mollugo cell suspensions require -NAA for continued growthand cell division. The kinetics of -NAA uptake from the medium(B₅) by Galium cells was assessed using 1-¹⁴C -NAA in a standardratio of cells to medium (0.25 g: 2.5 cm³). It was found thatthe uptake of -NAA was rapid, over 90% being taken up within4 h. Cells which had accumulated -NAA for 4 h or more did notrelease it back into the medium. It was found that Galium cellsaccumulated -NAA against a significant concentration gradient;suggesting the participation of an active component in the uptakemechanism. The effect of free-space and surface adsorption onthe uptake of -NAA was determined by means of a repeated washtechnique. These two factors were found to be of importanceonly during the first hour of uptake. Neither dead cells norplasmolysed cells absorbed -NAA. It is clear that, in the normal growth cycle, Galium cells cantake up the available -NAA within 3 or 4 h of inoculation andthat this can stimulate a cell division response of 3-4 generationsover the subsequent 14 d. Key words: Galium, cell suspension, -naphthalene acetic acid     

Interactions Between the Uptake and Assimilation of Inorganic Nitrogen and Carbon in Amphidinium spp. (Dinophyceae)

The rate of exponential growth of Amphidinium carterae Hulburtwas the same (0.025 h^–1) with either or as sole N-source. Nevertheless, in short-term experiments, cells growing exponentially with as N-source took up added 5–6 times faster than . accumulated in the cells. Addition of inhibited, reversibly, disappearance of from the medium; prior N-deprivation of the cells did not affect this inhibition. N-repIetecells, grown with as N-source, took up for several hours both in light and darkness, butthe uptake by such cells soon ceased in darkness although it continued in light. When uptake ceased, the cells could still take up rapidly in darkness. Ammonium taken up was assimilated rapidly into organic-N includingglutamine, other amino acids and protein. Ammonium uptake in darkness was accompanied by the utilizationof cellular polysaccharide, mainly glucose polysaccharide. Mostof this carbon was unavailable for the dark assimilation of. Addition of the analogue, methylammonium, did not initiate polysacchande catabolism. Itis suggested that a control mechanism is in operation, througha product of assimilation, which operates on one or more of the enzymes concerned with polysaccharidebreakdown, for example, -amylase or phosphorylase. Uptake of was accompanied by a high rate of dark ¹⁴CO₂ fixation and with both Amphidintum klebsii Kof.et Swezy and A. carterae N-deprivation led to a marked increasein this rate following addition of ; addition of had much less effect. The possible implications of these findings for the eco-physiology of marine dinoflagellatesare discussed. Key words: Ammonium, nitrate, CO₂ fixation     

Physiological Responses to Drought of Lolium perenne L.: Measurement of, and Genetic Variation in, Water Potential, Solute Potential, Elasticity and Cell Hydration

Thomas, H. 1987. Physiological responses to drought of Loliumperenne L.: Measurement of, and genetic variation in, waterpotential, solute potential, elasticity and cell hydration.—J.exp. Bot. 38: 115–125. Clonally-replicated genotypes of Loiium perenne L. were grownin a controlled environment. Leaf water potential (_w) osmoticpotential (_s), turgor potential (_p = _w – _s), elasticity(E), leaf hydration (g water per g dry matter, H) and numberof green leaves per tiller (N_GL) were measured before and duringa 42 d drought treatment. A simplified method of estimating E (at _w < 1?0 MPa) usingonly six measurements was developed to permit a measurementrate of 8 leaves per hour. Measurement errors in all characterswere 3% or less. During drought, _w and _s (at _w = 0?5 MPa) decreased significantly,_p and E increased significantly, and H decreased slightly. Plantsize during drought was negatively correlated with _s, and ^Hand positively correlated with _p, osmotic adjustment, E andN_GL. Measurements made on the genotypes before draughting didnot give a reliable indication of their physiological conditionafter adaptation to drought. Genetically controlled variation (‘broad sense heritability’)of drought-adapted plants for E was 15%, _w 23%, _s, 34%, _p, 35%,H 34% and N_GL 64%. The possibilities for, and effectivenessof, divergent selection of genotypes with high and low expressionof the characters are discussed. Key words: Water relations, Lolium, genetic variation     

Effects of Priming and Endosperm Integrity on Seed Germination Rates of Tomato Genotypes: II. GERMINATION AT REDUCED WATER POTENTIAL

Seed germination rates (GR =inverse of time to germination)are sensitive to genetic, environmental, and physiological factors.We have compared the GR of tomato (Lycopersicon esculentum Mill.)seeds of cultivar T5 to those of rapidly germinating L. esculentumgenotypes PI 341988 and PI 120256 over a range of water potential(). The influence of seed priming treatments and removal ofthe endosperm/testa cap enclosing the radicle tip on germinationat reduced were also assessed. Germination time-courses atdifferent 's were analysed according to a model that identifieda base, or minimum, allowing germination of a specific percentage(g) of the seed population (_b(g)), and a ‘hydrotime constant’(_H) indicating the rate of progress toward germination per MPa.h.The distribution of _b(g) determined by probit analysis was characterizedby a mean base (_b) and the standard deviation in _b among seeds(_b). The three derived parameters, _b, _b) and _H, were sufficientto predict the time-courses of germination of intact seeds atany . A normalized time-scale for comparing germination responsesto reduced is introduced. The time to germination at any (t_g())can be normalized to be equivalent to that observed in water(t_g(0)) according to the equation t_g(0)=[l–(/_b(g))]t_g().PI 341988 seeds were more tolerant of reduced and had a morerapid GR than T5 seeds due to both a lower _b and a smaller _H.The rapid germination of PI 120256, on the other hand, couldbe attributed entirely to a smaller _H. Seed priming (6 d in–1.2 MPa polyethylene glycol 8000 solution at 20 ?C followedby drying) increased GR at all >_b(g), but did not lower theminimum allowing germination; i.e. priming reduced _H withoutlowering _b. Removing the endosperm/testa cap (cut seeds) markedlyincreased GR and lowered the mean required to inhibit germinationby 0.7 to 0.9 MPa. However, this resulted primarily from downwardadjustment in _b during the incubation of cut seeds at low inthe test solutions. The difference in _b between intact and cutseeds incubated at high was much less (0.l MPa), indicatingthat at the time of radicle protrusion, the endosperm had weakenedto the point where it constituted only a small mechanical barrier.In the intact seed, endosperm weakening and the downward adjustmentin embryo _b ceased at < –0.6 MPa, while the reductionin _H associated with priming proceeded down to at least –1.2MPa. Based on these data and on the pressure required to pushthe embryos from the seeds at various times after imbibition,it appears that the primary effect of priming was to shortenthe time required for final endosperm weakening to occur. However,as priming increased GR even in cut seeds, priming effects onthe embryo may control the rate of endosperm weakening. Key words: tomato, Lycopersicon esculentum Mill., water potential, germination rate, seed priming, genetic variation     

Cyclic AMP Promotion and Abscisic Acid Inhibition of {alpha}-Amylase Activity in the Seeds of Rice (Oryza sativa L.)

Cyclic AMP and GA₃ stimulated both -amylase activity in riceendosperm and the germination of the seed. In combination theyalso induced germination of ABA-treated seeds but cyclic AMPalone failed to neutralize the inhibitory effect of ABA; withadded kinetin, however, it promoted the -amylase activity ofthe dormant seeds. The enzyme activity decreased as the storageperiod of seeds increased. Cyclic AMP and GA     

Potassium Transport Across the Membranes of Chara: II.42K FLUXES AND THE ELECTRICAL CURRENT AS A FUNCTION OF MEMBRANE VOLTAGE

Smith, J. R. 1987. Potassium transport across the membranesof Chara. II. ⁴²K fluxes and the electrical current as a functionof membrane voltage.—J. exp. Bot. 38: 752–777. The current required to clamp the trans-membrane voltage ofinternodal cells of Chara australis at different levels wasmeasured simultaneously with either the ⁴²K influx or efflux.Examination of the voltage-dependence of the ratio of the electricalcurrent to the unidirectional tracer fluxes yielded no evidenceof any amplification of the electrical driving force on theK⁺ ions. There was thus no evidence for the interaction of K⁺ions with themselves or any other species during their passageacross the membrane. These measurements allow the determinationof , the fraction of the electrical current carried by K⁺ ions.When the external [K⁺] = 10 mol m^–3, the average valueof was 0?85 for V_m > –125 mV and 07?5 for V_m <–150 mV. When the external [K⁺] = 0?1 mol m^–3, was 0?6 for V_m < –80 mV and 0?1 for V_m > –250mV. It was also found that the conductance associated with K⁺transport was inhibited by hyperpolarization. Key words: Potassium, conductance, flux-ratio     

The Preparation and Characterization of an Aggregated Gliadin Fraction from Wheat

An aggregated gliadin fraction was prepared by gel filtrationon Sephacryl S300 in a solvent containing 6.0 M guanidine hydrochloride.This was reduced, alkylated, and separated by ion exchange chromatography.SDS-PAGE of the resulting fraction showed a number of polypeptides,mostly with apparent M¹s of around 44 000. The amino acid compositionwas similar to those reported previously for monomeric -, ß-and -gliadins. Automated amino acid sequencing from the N-terminusalso showed the presence of sequence types characteristic of-, ß-, and -gliadins, but the major sequence typewas not related to any described previously. This sequence wasNH₂-Ser-His-Ile-Pro-Gly-Leu-Glu-Arg-Pro-Ser-Gln-Gln-Gln-Gln-Leu-. Key words: Wheat, Gluten, Gliadin, Seed     

The Meaning of Matric Potential

The commonly used equation, = P - + , which describes thepartitioning of plant water potential, , into components ofhydrostatic pressure, P, osmotic pressure, , and matric potential,, is misleading. The term , which is supposed to show the influenceof a solid phase on , is zero if a consistent definition ofpressure is used in the standard thermodynamic derivation. However,it can be usefully defined by = + _D, where _D is the osmoticpressure of the equilibrium dialysate of the system. The practicaland theoretical significance of this definition is discussed.     

Effect of Nitrogen Form and Counterion on Establishment of the Rhizobium trifolii-Trifolium repens Symbiosis

The effect of level of different counterion forms of or or both, on establishment of the Rhizobium trifolii-Trifolium repens symbiosis was evaluatedin plants cultured under bacteriologically controlled conditions. Ammonium had little effect on nodule formation, and even after exhaustion there was little compensatory nodule formation. Plant growth, nodule mass and acetylene reductionactivity all declined with increasing levels of . Except for , different counterion forms had little effect on plant growth, nodule numberand mass, and acetylene reduction activity. Ammonium markedlydecreased pH, the extent being dependent upon level and counterion present. Nitrate inhibited nodulation while levels remained in excessof plant uptake. Compensatory nodulation followed exhaustionof or at lower or levels. Nodule mass and acetylene reduction activity decreased, but plant growth increased withincreasing or levels. Nitrate raised the pH of the nutrient solution by one unit orless. Different or counterion forms had little effect on the symbiosis or plant growth. Ammonium nitrate severely inhibited nodulation but on exhaustionmarked compensatory nodulation occurred. The patterns of nodulemass, acetylene reduction activity and plant growth with increasingNH₄NO₃ levels were similar to or alone. Plants provided with NH₄NO₃ or no nitrogenwere similar in only slightly decreasing pH. Key words: Ammonium, Nitrate, Ammonium nitrate, Nitrogen fixation, Rhizobium trifolii, Trifolium repens, Symbiosis establishment, Nodulation