The Absorption of Ions by Excised Root Systems: II. OBSERVATIONS ON ROOTS OF BARLEY GROWN IN SOLUTIONS DEFICIENT IN PHOSPHORUS, NITROGEN, OR POTASSIUM

1. Barley plants were grown in complete culture solution and indeficiencies of phosphorus, nitrogen, or potassium for a periodof about 6 weeks. Excised roots of these plants were treatedwith a complete, aerated culture solution at 25? C. for varyingperiods of time, and the changes in respiration rate, phosphorus,nitrogen, potassium, sugars, and starch contents measured.
2. Therewere changes in fresh weight and dry weight of the excisedrootsduring treatment. The dry weight decreased with time butthewater-content changes were variable. There was a gain orlossof water by the roots according to the treatment.
3. In all casesthe deficient roots increased in content of theelement in whichthey were originally deficient. The roots ofthe plants suppliedwith full nutrient usually decreased incontent of phosphorus,nitrogen, and potassium, but exceptionsoccurred and the reasonsare discussed.
4. In most of the experiments described simultaneousloss of oneion and gain of another occurred.
5. Nitrogen-deficientroots accumulated nitrate when exposed toa complete nutrientsolution, and some of this was assimilatedwith formation ofprotein. Under similar conditions nitrogen-richroots decreasedin nitrogen content and proteolysis took place.
6. There wasa rapid fall in sucrose and reducing sugar contentof the excise'roots. The starch content was initially verysmall and showedlittle change with time.
7. The respiration rate declined withtime in all treatments exceptwhere a nitrogen deficiency existed.Here the respiration rateincreased to a maximum value at about8 hours and then fell.This increase in rate is attributed toprotein synthesis. Noevidence of a ‘salt respiration’was observed evenwhen active uptake of phosphorus or potassiumwas occurring.
8. In most instances the carbon dioxide evolvedin respirationgreatly exceeded the carbon dioxide equivalentof the sugarconsumed in the same period. Exceptions were foundwith thenitrogen-deficient roots where less carbon dioxidewas evolvedthan the equivalent of sugar consumed. It is probablethat apart, at least, of the sugar unaccounted for was usedin proteinsynthesis.
9. Where the carbon dioxide of respirationwas in excess of theequivalent of sugar consumed, protein oramino-acid is the mostprobable substrate. Respiration rateis found to be relatedboth to nitrogen and sugar content.

     

Studies on the Germination of the Seeds of Striga hermonthica: II. THE EFFECT OF THE STIMULATING SOLUTION ON SEED RESPIRATION

1. Data are presented which show the effect of the natural stimulatingsolution on the respiration of the seeds of Striga hermonthica.
2. The stimulating solution has been shown to enhance the aerobicrespiration of seeds exposed to it, compared with that of seedsto distilled water at the same temperature. This effect on therespiration of the seeds is quite independent of any previousmoisture-treatment of the seeds, and thus of germination.
3. Themaximum anaerobic rate of carbon-dioxide output of air-dryseedsafter treatment with the stimulating solution may be upto fifteentimes greater than that of seeds moistened with distilledwater.The anaerobic respiration of air-dry seeds after exposuretothe stimulating solution is greatly reduced by 0?025 M. sodiumfluoride and 0?001 M. sodium monoiodoacetate.
4. The stimulatingsolution has been found to have little effecton the anaerobicoutput of carbon dioxide from seeds which hadbeen moisture-treatedfor 6 days at 22? C. before treatmentwith the stimulating solution.
5. No correlation could be established between the effects ofthestimulating solution on germination and respiration.

     

Organic Acid Metabolism of Sedum praealtum

1. The organic acids present are citric, isocitric, and l-malic,with a small residue of unidentified acids.
2. The diurnal variationin acidity is due chiefly to changes,in malic acid, with aparallel fluctuation shown by citric acid.Under these conditionsisocitric acid shows little change.
3. The importance of carbondioxide during acidification is confirmed,and it is shown thatat room temperatures or higher the CO₂produced in respirationis sufficient to produce maximum acidification.At lower temperaturesthe supply of CO₂ limits acid production.
4. In the absence ofoxygen no acidification occurs, but even smallquantities (approx.1 per cent.) are sufficient to cause someacid production.
5. Completebalance-sheets are presented for acids, carbohydrates,CO₂ andoxygen for leaves maintained in the dark at high andlow temperatures.As acids are produced there is a correspondingloss of carbohydrate(chiefly starch). A scheme of reactionsis suggested to explainthe experimental results.

     

Apparatus for the Measurement of Gaseous Conditions inside an Apple Fruit

1. Two forms of apparatus are described, one for the routine analysisof the internal atmosphere of an apple fruit and another forthe measurement of (i) carbon dioxide output, (ii) internalgas concentrations, (iii) atmospheric pressure within the fruit,(iv) permeability of the fruit to gases.
2. The use of thesetwo apparatuses to follow changes within thefruit as a resultof the application of a skin-coating is describedand the resultsobtained are discussed.
3. It is shown that the fall in pressurewhich occurs as a resultof the cooling of the fruit due toevaporation of the appliedcoating can only form a small fractionof the total fall inpressure observed as a result of the applicationof the coating.
4. It is shown that coating the fruit with anoil-water emulsioncauses a deficit in the combined concentrationof CO₂ and O₂within the fruit below the 21 per cent, observedin similaruncoated fruit.
5. An explanation of this phenomenonis advanced, and it is suggestedthat the modification of theinternal atmosphere brought aboutby the skin-coating, if itcan be suitably controlled, willprove valuable in increasingthe cold-storage life of apples.

The work described in this paper was carried out as part ofthe programme of the Food Investigation Organization of theDepartment of Scientific and Industrial Research.     

Effect of Modified Atmosphere Composition on the Metabolism of Glucose by Brochothrix thermosphacta

The influence of atmosphere composition on the metabolism of Brochothrix thermosphacta was studied by analyzing the consumption of glucose and the production of ethanol, acetic and lactic acids, acetaldehyde, and diacetyl-acetoin under atmospheres containing different combinations of carbon dioxide and oxygen. When glucose was metabolized under oxygen-free atmospheres, lactic acid was one of the main end products, while under atmospheres rich in oxygen mainly acetoin-diacetyl was produced. The proportions of the total consumed glucose used for the production of acetoin (aerobic metabolism) and lactic acid (anaerobic metabolism) were used to decide whether aerobic or anaerobic metabolism predominated at a given atmosphere composition. The boundary conditions between dominantly anaerobic and aerobic metabolisms were determined by logistic regression. The metabolism of glucose by B. thermosphacta was influenced not only by the oxygen content of the atmosphere but also by the carbon dioxide content. At high CO₂ percentages, glucose metabolism remained anaerobic under greater oxygen contents.     

The Isolation of l-Quinic Acid from the Apple Fruit

1. A method is described by means of which several grammes ofl-quinicacid were isolated from young fruits of the WorcesterPearmainapple stored for a number of days in nitrogen.
2. Theessential stages in the method are the removal of colouringmatter from extracts of the frozen ground pulp tissue of thefruit with charcoal, the removal of amino acids by absorptionon cation exchange resin, and the separation of the organicacid from sugars by adsorption of the former on anion exchangeresin. Finally, the quinic acid was separated from malic acidby fractional displacement from the anion exchange resin.
3. Thecharacterization of the isolated quinic acid, and of malicacidalso isolated from the fruits, is described.
4. Citric acid isshown to be formed by oxidation of quinic acidwith hot hydrogenperoxide.
5. The possible function of quinic acid in the applefruit andin plants generally is discussed.

     

The Absorption of Ions by Excised Root Systems: I. APPARATUS AND PRELIMINARY EXPERIMENTS

1. An apparatus is described by means of which the absorptionofions from a complete nutrient solution of constant compositionby excised root systems of plants, grown under known nutrientdeficiencies, may be measured in standard conditions of aerationand temperature. Results of some prelimi nary experiments aredescribed.
2. It was found that the roots readily absorbed theelement inwhich they were deficient, but tended to lose thoseelementswhich were already present in normal amounts.
3. Therewas almost invariably a loss in fresh weight of the rootsafterthe absorption period and also a loss in dry weight. Thislossappears to be complex and is partly attributable to lossofrespiratory material.
4. The addition of 2 per cent. sucroseto the solution from whichthe root systems of phosphorus-deficientbarley plants wereabsorbing increased the nitrogen and phosphoruscontents ofthe roots and maintained the potassium content,while in absenceof sucrose only the phosphorus content increased,but this increasewas significantly less than in the presenceof sucrose.
5. It was shown that roots excised from plants growingin soilwere capable of absorbing phosphorus or nitrogen—elementsin which they were apparently deficient.
6. The interpretationof data obtained from excised roots is discussed,and it isconcluded that excised roots from plants grown incomplete nutrientare not likely to behave in the same way,as regards absorption,as corresponding roots of intact plants,but that roots grownunder conditions of deficiency will behaverather similarlywhether excised or intact. This fact providesa potential methodfor diagnosing and evaluating nutrient deficiencies.
7. The low-saltcondition of roots postulated by Hoagland and Broyeris notnecessarily the primary requisite for rapid absorptionof aparticular ion. It is rather that the roots should be deficientin that ion. The roots could be high in other salts.

     

The Organic Acid Metabolism of Bramley's Seedling Apple Peel1

1. The effect of various Krebs cycle acids on the respirationofdisks of apple peel at various stages of maturity was measuredin a Warburg respirometer.
2. Peel tissue from apples at thepre-climacteric and early post-climactericstages apparentlycontain sufficient of the Krebs cycle acidsused, with the exceptionof succinate, to maintain oxidativeprocesses at a maximum.
3. The addition of malate causes a large increase in the CO₂-outputof peel from post-climacteric and senescent fruit but not frompre-climacteric fruit, and a close correlation exists betweenthe climacteric and this decarboxylation of malate. The decarboxylationof malate does not affect the rate of O₂-uptake of peel tissue.The possible part played by the decarboxylation of malate inthe increased CO₂-output at the climacteric is discussed.
4. Addedpyruvate is decarboxylated by the tissue at all stagesof storagelife.
5. The decarboxylation of added malate is an aerobic fermentation,resulting in the quantitative production of acetaldehyde. Althoughthe presence of oxygen is necessary, the rate of O₂-uptake isnot affected by the reaction. Pyruvate decar boxylation doesnot require the presence of oxygen.
6. The O₂-uptake of peelfrom senescent apples can be stimulatedby addition of malate,succinate, and a-ketoglutarate. No evidencewas obtained, however,of oxidation of fumarate, citrate, orpyruvate. The additionof malate to senescent tissue restoresthe lower endogenousrate of O₂-uptake to that of early postclimacteric tissue.
7. Succinate and fumarate are toxic to peel tissue at concentrationabove 0.02M.

     

Control of photosynthesis during nitrogen depletion and recovery in a non-nitrogen-fixing cyanobacterium

When cells of Synechocystis strain PCC 6308 are starved for nitrogen, the amount of stored carbohydrate increases, the phycocyanin to chlorophyll a ratio decreases, and the rates of oxygen evolution and of carbon dioxide fixation decrease. When nitrate-nitrogen is replenished, the amount of carbohydrate decreases, the rate of oxygen evolution increases immediately, preceeding the increase in phycocyanin or carbon dioxide fixation. The rate of respiration first increases and then decreases upon nitrogen addition. Nitrogen-starved cells show no variable fluorescence; variable fluorescence recovered in parallel with oxygen evolution. This suggests that photosystem II is inactive in nitrogen depleted cells and not blocked by a build up of metabolic endproducts. Since carbon dioxide fixation does not increase until two to four hours after nitrate is replenished to nitrogen starved cells, it is suggested that reducing power may first be needed within the cell for some other process than photosynthesis, such as nitrate reduction.     

CHANGES IN CONTENTS OF CARBOHYDRATE AND FATTY ACID IN THE CELLS OF CHLORELLA PROTOTHECOIDES DURING THE PROCESSES OF DE- AND RE-GENERATION OF CHLOROPLASTS

1. Previous work has demonstrated that when cells of Chlorellaprotothecoides are grown mixotrophically under illuminationin a medium rich in nitrogen source (urea) and poor in glucose,normal green cells are obtained, while in a medium rich in glucoseand poor in the nitrogen source, strongly bleached cells containingapparently no discernible chloroplast structures — called"glucose-bleached" cells — are produced either in thelight or in darkness. When the green cells are incubated ina glucose-enriched mineral medium without added nitrogen source,they are fairly rapidly bleached with concomitant degenerationof chloroplast structures (" bleaching "). When, on the otherhand, the "glucose-bleached" cells are transferred in a nitrogen-enrichedmedium without added glucose under illumination, they turn greenwith regeneration of chloroplasts (" greening "). In the presentstudy changes in contents of carbohydrate and fatty acid inalgal cells were followed during these processes of "bleaching"and "greening.".
2. During the process of "bleaching", the quantityof glucose existingin the insoluble carbohydrate fraction ofalgal cells increasedrapidly and markedly. A considerable increasewas also observedin the contents of cells in oleic, linoleicand palmitic acids.It was noted, however, that linolenic aciddecreased in quantityduring the most active phase of cell bleaching.
3. During the process of "greening", the glucose in the insolublecarbohydrate fraction rapidly decreased, suggesting that itis utilized, as carbon and energy sources, for the chloroplastregeneration. Linolenic acid was found to be synthesized inparallel with formation of chlorophyll. A peculiar pattern ofchange in contents was observed with oleic and palmitic acids,which was interpreted as being related with the process of cellulardivision occurring incidentally during the process of greening.

(Received September 24, 1966; )     

Observations on the Gaseous Exchanges which take place between Menyanthes trifoliata L. and its Environment: I. THE COMPOSITION OF THE INTERNAL GAS OF THE PLANT

1. As part of a general investigation into the exchange of gasesbetween the bogbean, Menyanthes trifoliata, and its environment,determinations have been made of the composition of the internalatmosphere of the plant at five different levels, viz. leafyshoot, three successive portions of stem, and roots.
2. Procedureis described for the analysis of small gas samplesusing a modificationof the Bonnier and Mangin apparatus.
3. In darkness with thelower part of the plant surrounded by anatmosphere of nitrogen,it has not been possible to show thepresence of a regular downwardsgradient of oxygen, such aswould be expected on a basis ofnormal gaseous diffusion.
4. Under these Air Top/Nitrogen Bottomconditions the roots areshown to contain between 12?5 and 17?5percent, of oxygen intheir intercellular gas system. The portionof stem immediatelyadjacent to the roots showed an oxygen levelof from 14?0 to18?0 per cent.
5. In plants kept under NitrogenTop/Air Bottom conditions in thedark for 48 hours, the concentrationof oxygen in the rootsfell to a level of 3?1 per cent, or belowin three plants andto 6?o per cent, in a fourth. The oxygenconcentration in theadjacent lowermost part of the stem wasas high as 18?0 percent., depending on the degree of aerationof the solution bathingthe stem. It is suggested that thisdistribution of oxygen canbe related to the relative impermeabilityof roots and of stemendodermis to gaseous diffusion from without,and it is thoughtthat the major part of the oxygen supply tothe roots is transportedto them through the stelar air passages.
6. Some evidence is presented to show that oxygen passes fromthelower parts of the plant into the medium surrounding it.

     

Further Studies on the Acid Metabolism of Aspergillus niger: THE FORMATION AND UTILIZATION OF OXALIC ACID

1. Some recent works on the formation of oxalic acid by variousfungi are critically considered.
2. The present work deals withthe role of oxalic acid in the metabolismof Aspergillus niger.
3. When glucose solutions were supplied to preformed mats ofthefungus oxalic acid accumulated, attaining an equilibriumlevelwhich was not exceeded despite the presence of a considerableconcentration of glucose.
4. When the glucose supplies were depletedthe oxalic acid concentrationfell steeply to a low level.
5. Theconcentration of oxalic acid was dependent on the glucoseconcentration.In three separate series of experiments it wasshown that theoxalic acid concentration diminished with increasingglucoseconcentration.
6. Similar results were obtained when the cultureswere rearedfrom spores on culture solutions with the normalamounts ofnutrient salts but different glucose concentrations.
7. In all cases the CO₂ output increased with the glucose concentration.
8. When cultures were supplied with glucose+oxalic acid, theconcentrationof the latter fell steeply to the equilibriumlevel attainedon glucose only. In a culture receiving glucose+oxalicacid,with the oxalic acid concentration somewhat below thenormalequilibrium concentration, the formation of oxalic acidfromthe glucose ceased as soon as the equilibrium level hadbeenattained.
9. When 1 per cent. oxalic acid only was suppliedto the fungusthe concentration gradually diminished to a lowlevel. When3 per cent. oxalic acid was supplied the rate ofacid utilizationsoon fell to low value.
10. In several experimentsit was shown that the rate of CO₂ outputwas higher from culturessupplied with glucose+excess oxalicacid than from culturessupplied with glucose only.
11. The rate of oxalic acid carbonloss was always below that ofthe CO₂ carbon output both incultures supplied with oxalicacid only and in cultures receivingglucose+oxalic acid.
12. The cultures were incapable of utilizingneutral sodium oxalateand the presence of this substance hadno effecft on the ofCO₂ output.
13. The results indicate thatthe utilization of oxalic acid isassociated with the liberationof at least an equivalent amountof CO₂.
14. It is suggested thatthe utilization of oxalic acid is promotedby the presence ofglucose, thus accounting for the lower oxalicacid concentrationsand higher rates of CO₂ output of cultureswith higher glucoseconcentrations.

     

The Diageotropic Behaviour of Rhizomes

1. The geotropic behaviour of rhizomes of Aegopodium podagrariahas been investigated by time-lapse photographic recording usinginfra-red radiation in complete absence of light.
2. They havebeen shown to be very sensitive to light. Even a singleexposurefor 30 seconds to red light evokes a characteristicresponsein which the rhizome first turns downwards and thenturns upagain to the horizontal position. The exposure to lightduringthe process of digging up the rhizomes and setting upin theapparatus has similar effects which die away after about24hours.
3. After recovery from this initial light effect theycontinueto grow roughly horizontal if maintained in darknessor subjectedto infra-red radiation only. If inverted (turnedthrough 180?)the side which was lowermost during the inversiongrows forabout 2 hours relatively the more quickly, thus becomingconvex;then a rapid straightening and bending in the oppositedirectionoccurs. This is followed by further up-and-down movementswhichgradually die out and the rhizome then continues growingstraight.
4. Inversion for 10 minutes also evokes an essentiallysimilarresponse, which begins about 20 minutes after the invertedrhizomehas been returned to its original position. The importanttheoreticalsignificance of this is discussed in the text.
5. Displacementof rhizomes through angles other than 180? resultsin to-and-frobendings in which the side of the rhizome whichwas uppermostbefore the stimulus of displacement first becomesconvex. Therhizomes then turn gradually towards the horizontalplane.
6. Rhizomeswhich have recovered from the initial light effectand are thusgrowing in darkness horizontally are caused toturn upwardswhen the air surrounding them is replaced by air+5per cent,carbon dioxide.
7. The theoretical significance of these findingsis discussed.

     

The Metabolism of Acetaldehyde by Plant Tissues

Apples and oranges can absorb appreciable amounts of acetaldehydevapour, but acetaldehyde does not accumulate in the tissues,in the presence or absence of oxygen. When the fruit is givenacetaldehyde the loss of carbon as CO₂ + ethanol equals thatlost from carbohydrate + acid+acetaldehyde. Part of the addedacetaldehyde is reduced to ethanol by NADH₂ and the rate ofglycolysis is increased; the remainder is oxidized to CO₂. Respiration of apples is limited by oxygen; the output of CO₂is only slightly increased at the beginning of the treatmentwith acetaldehyde, but afterwards it declines; acetaldehydespares oxidation of carbohydrate. In oranges, availability of substrate limits respiration, andacetaldehyde stimulates CO₂-production and O₂-uptake. In theabsence of oxygen, acetaldehyde is reduced to ethanol, and thequotient CO₂/ethanol falls.     

REDUCTION OF CARBON DIOXIDE COUPLED WITH THE OXYHYDROGEN REACTION IN ALGAE

1. Unicellular algae possessing a hydrogenase system (Scenedesmus and other species), and having been adapted by anaerobic incubation to the hydrogen metabolism, reduce oxygen to water according to the equation O₂ + 2H₂ → 2H₂O. 2. The oxyhydrogen reaction proceeds undisturbed only in the presence of carbon dioxide, which simultaneously is reduced according to the equation CO₂ + 2H₂ → H₂O + (CH₂O) = (carbohydrate). 3. The maximum yield of the induced reduction is one-half molecule of carbon dioxide reduced for each molecule of oxygen absorbed. 4. Partial reactions are recognizable in the course of the formation of water and it is with the absorption of the second equivalent of hydrogen that the carbon dioxide reduction appears to be coupled. 5. The velocity of the reaction increases in proportion to the partial pressure of oxygen, but only up to a certain point where any excess of oxygen causes the inactivation of the hydrogenase system. The reaction then ends prematurely. 6. During the oxyhydrogen reaction little or no oxygen is consumed for normal respiratory processes. 7. Small concentrations of cyanide, affecting neither photosynthesis nor photoreduction in the same cells, first inhibit the induced reduction of carbon dioxide and then lead to a complete inactivation of the hydrogenase system. 8. Hydroxylamine, added after adaptation, has either no inhibitory effect at all, or prevents solely the induced reduction of carbon dioxide without inactivating the hydrogenase system. 9. Dinitrophenol prevents the dark reduction of carbon dioxide while the reduction of oxygen continues to the formation of water. 10. Glucose diminishes the absorption of hydrogen, probably in its capacity as a competing hydrogen donor. 11. The induced reduction of carbon dioxide can be described as an oxido-reduction similar to that produced photochemically in the same cells.     

Anaerobic mineralization of cholesterol by a novel type of denitrifying bacterium

A novel denitrifying bacterium, strain 72Chol, was enriched and isolated under strictly anoxic conditions on cholesterol as sole electron donor and carbon source. Strain 72Chol grew on cholesterol with oxygen or nitrate as electron acceptor. Strictly anaerobic growth in the absence of oxygen was demonstrated using chemically reduced culture media. During anaerobic growth, nitrate was initially reduced to nitrite. At low nitrate concentrations, nitrite was further reduced to nitrogen gas. Ammonia was assimilated. The degradation balance measured in cholesterol-limited cultures and the amounts of carbon dioxide, nitrite, and nitrogen gas formed during the microbial process indicated a complete oxidation of cholesterol to carbon dioxide. A phylogenetic comparison based on total 16S rDNA sequence analysis indicated that the isolated micro-organism, strain 72Chol, belongs to the β2-subgroup in the Proteobacteria and is related to Rhodocyclus, Thauera, and Azoarcus species. Received: 16 July 1996 / Accepted: 5 December 1996     

A re-examination of the problem of photochemical nitrogen reduction by blue-green algae

Summary Although it was possible in the light in the absence of carbon dioxide to obtain a ratio of nitrogen fixed to oxygen evolved in nitrogen-starved cells of A. cylindrica near to 1:1.5, that quoted by other workers, ratios varying between 1:0.9 and 1:3.0 were also obtained. The amount of oxygen evolved under the same conditions by normal cells in the presence of pyruvate was increased considerably. Since the addition of pyruvate also resulted in increased carbon dioxide output in the dark with the same algal material, oxygen output in the light was attributed to the production of factors necessary for carbon assimilation.Addition of pyruvate to nitrogen-starved and normal cells in the light resulted in similar rates of oxygen evolution after an initially higher rate in the starved cells. The ratio of overall nitrogen fixed to oxygen evolved, was 1:6.6 for the starved cells and 1:6.4 for the normal cells, showing that the presence of an added substrate increased oxygen output relative to nitrogen uptake. ¹⁴CO₂ was recovered from sodium pyruvate-1-¹⁴C in flasks incubated in the dark, showing that, at least in the dark, pyruvate was decarboxylated.The interpretation of these results is that endogenous and exogenous substrates available to cells of A. cylindrica become decarboxylated and that, in the light, carbon dioxide produced may be assimilated photochemically with accompanying oxygen evolution. This interpretation has been discussed in relation to reports of photochemical nitrogen reduction in blue-green algae.     

Energetics of Saccharomyces cerevisiae CBS 426: Comparison of anaerobic and aerobic glucose limitation

Saccharomyces cerevisiae CBS 426 was grown aerobically and anaerobically in a glucose-limited chemostat. The flows of biomass, glucose, ethanol, carbon dioxide, oxygen, glycerol, and the elemental composition of the biomass were measured. Models for anaerobic and aerobic growth are constructed. Values for Y_ATP and P/O are obtained from continuous culture data for aerobic growth; this Y_ATP value is compared with that obtained from the anaerobic growth results. The ratio between the heat produced and the oxygen consumed increases if more glucose in fermented to ethanol and carbon dioxide. An equation for ?_H/?_O as a function of the respiratory quotient is given.     

Oxygen Evolution from Algae Illuminated by Short and Long Flashes of Light

The oxygen produced by illuminating Ankistrodesmus braunii withsingle light flashes has been determined using the Hersch galvanicoxygen cell. Measurements were made with the cells suspendedin alkaline solution equilibrated with nitrogen containing oxygenat a partial pressure of 10^–4 mm. Hg.

1. A single light flash, if very brief (less than 5 millisec.)results in no measurable oxygen production; a longer flash (35millisec.) gave a yield of approximately 1 mole O₂/800 moleschlorophyll.
2. A pair of flashes suitably spaced gave a greateryield thanthe sum of the yields when given individually, althoughonewas so brief that by itself it produced no measurable oxygen.The yield of a long flash preceded by a short flash was twiceas great as that of the long flash given alone; when the flashorder was reversed the combined yield was smaller but stillgreater than for the long flash alone.
3. The combined yieldof a pair of flashes varies with the intervalseparating theflashes, rapidly rising to a maximum and thendecaying moreslowly. With a long and short flash the optimalinterval was0.7 sec. but some enhancement of yield was observedwhen theflashes were separated by as long as 10 or 15 sec.
4. When theflashes were superimposed on background illuminationthe yieldswere increased and were measurable even for the shortflashes.Measured with background illumination the optimal yieldfora pair of short flashes was obtained with flashes separatedby about 0.05 sec.

     

Factors concerned in the Rooting Responses of Isolated Leaves

The rooting responses of isolated leaves of the dwarf Frenchbean and the ivy were studied by applying solutions of growthsubstances to the petiole: ß-indolyl-butyric acid(I.B.A.) for the former and -naphthyl-acetic acid (N.A.A.) forthe latter. The following factors were investigated:

1. The variation in response of successive leaves from the apextowards the base of the plant.
2. The optimal concentrationsof the growth substances and therelation between duration ofapplication and concentration.
3. The relation of age of theleaf and optimal concentration(ivy).
4. The nutritive factorsconcerned in the response were studied,(a) by varying periodsof contact between lamina and petiole,(b) by varying durationof light, (c) by varying the amountof light, and (d) by feedingwith sucrose and asparagine.

The most responsive leaf in the bean was the 2nd from the apex,in the ivy the 9th leaf. Very young leaves were killed. Withpetioles immersed for 24 hours the optimal concentrations wereI.B.A. at 2·5 parts per million (p.p.m.) for the bean,and N.A.A. 100 p.p.m. for the ivy. It was shown that the activesubstance entered mainly through the cut end in the transpirationstream; entry through the cuticle was much slower. Starvation of the cuttings whether by low light intensity, darkness,or separation of the lamina from the petiole reduced root formation.Feeding with sucrose and asparagine increased the response. Analysis of the leaves was carried out at regular intervalsfor total sugar, total and soluble nitrogen. In the bean solublenitrogen increased slightly in the petiole during the first5 days after treatment, after which insoluble nitrogen continuedto accumulate until the 7 day, when the roots first emerged.After this the total nitrogen decreased. Sugar content of thepetiole at first increased but rapidly fell before the rootsemerged and then again increased. In the ivy petiole the increasein soluble and total nitrogen was very slow, the former beinggreatest on the 15th day and the latter on the 20th day aftertreatment. The total sugar increased to the 10th day, but thendecreased until the emergence of roots, after which it againincreased. Treated leaves of the bean and ivy of different agesand the leaves starved for varying periods were also analysedfor total sugars and total nitrogen. Treated bean leaves receivingvarying periods of daily illumination were also analysed toelucidate their rooting response. Histological examination showed that in the bean the roots arosein the rays between the vascular bundles and in the ivy externalto the vascular bundles opposite the phloem. The growth of the rooted leaves was followed for more than amonth in the bean and over one year in the ivy. Some growthwas found in the immature bean leaves which survived treatment,but the final size was much below that of the control leavesattached to the plant. In the ivy very little further growthoccurred although the leaves produced a large root system andafter 2 years are still alive: the original differences in sizeof the successive leaves at the time of removal from the plantstill remain.