PHOTOCHEMICAL INTERCONVERSION BETWEEN PRECURSORS OF PHYCOBILIN CHROMOPROTEIDS IN TOLYPOTHRIX TENUIS

1. The photochemical conversion between the precursors of phycocyaninand phycoerythrin in Tolypothrix tenuis was investigated.
2. Itwas found that the conversion of phycocyanin-precursor intophycoerythrin-precursor was induced by green light, and thereverse reaction by red light. These reactions proceeded exponentially, indicating that the photochemical process was acceleratedautocatalytically by the reaction-product.
3. The rates of thesephotochemical reactions were found to beunaltered by varyingthe incubation temperature (0? to 35?)and the composition ofthe gas atmosphere (presence or absenceof CO₂ and of O₂ orby an inhibitor of photosynthesis, p-chlorophenyldimethylurea.
4. The action spectra of the photochemical interconversions betweenprecursors of phycobilin chromoproteids were found to be distinctlydifferent from the absorption spectra of chlorophyll and carotenoids.The most effective wavelength for inducing the conversion ofphycocyanin- into phycoerythrin-precursor (541 mµ) isnear the absorption maximum of phycoerythrin (565 mµ),and that of the reverse reaction (641 mµ) is near theabsorption maximum of phycocyanin (620 mµ). Additionaldata, indicating that the phycobilin chromoproteids themselvesdo not participate in these processes as light absorber, werealso presented.
5. On the basis of these results, a possiblemechanism of the photochemicalinterconversion between the precursorsof phycobilin chromoproteidsis proposed.

(Received March 13, 1962; )     

Polyphenoloxidase and the Respiration of Ivy Leaves

1. Polyphenoloxidase is present in ivy leaves but not in thoseof Aucuba or Euonymus.
2. Respiration of intact ivy leaves wasmarkedly stimulated bycatechol (R.Q. approximately=I), gallicacid, caffeic acid,and dihydroxyphenylalanine. The stimulationwas not relatedto injury as far as could be detected and wasnot followed byinhibition. The extra oxygen consumption representsa many timesrepeated oxidation of the amount of catechol supplied.
3. The effect of catechol on the respiration of Aucuba and Euonymusleaves was very small.
4. Cupferron and phenylthiourea, whichinhibit polyphenoloxidasein vitro, nevertheless increased respirationwhen administeredto leaves through the petiole. On the otherhand, when appliedby infiltration, cupferron did cause inhibition,but in Aucubaand Euonymus as much as in ivy.

     

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.

     

SYNCHRONOUS CULTURE OF CHLORELLA: II. CHANGES IN CONTENT OF VARIOUS VITAMINS DURING THE COURSE OF THE ALGAL LIFE CYCLE

1. Chlorella ellipsoidea was grown synchronously and the changesin content of various vitamins during the algal life cycle werefollowed either by chemical or microbiological assay methods.
2. In terms of µg per gram of cell dry weight, the contentof some vitamins (niacin, biotin, inositol and choline) remainedalmost constant throughout the algal life cycle, while thatof others (vitamin B₆-complex, pantothenic acid, folic acid,thiamine and riboflavin) was found to decrease more or lessmarkedly during the "growing phase" and increase at later phasesof "ripening". The content of p-aminobenzoic acid increasedonly at an early stage of "ripening", and that of ascorbic acidincreased only at the stages in which photosynthesis occurredmost actively.
3. These results were discussed in an attemptto interprete theirrelationship with the previously reportedobservations pertainingto the physiological and biochemicalevents occurring in thelife cycle of the alga.

(Received November 7, 1959; )     

Studies in the Nitrogen Metabolism of Apple Fruits: THE CLIMACTERIC RISE IN RESPIRATION IN RELATION TO CHANGES IN THE EQUILIBRIUM BETWEEN PROTEIN SYNTHESIS AND BREAKDOWN

1. A close parallelism in the drift of the rate of respirationand the protein-N/ non-protein-N ratio is shown to occur bothin apple fruits attached to the tree and when detached fromthe tree at various stages of development and stored for severalmonths at 12 C.
2. In detached fruits the fall in respirationwhich occurs immediately(during the first 48 hours) after pickingis only accompaniedby a concomitant fall in net protein invery young fruits inwhich active cell division is taking place.Subsequently, infruit of all ages when a climacteric rise inrespiration occursit is accompanied by a net increase in protein.
3. It is argued that the climacteric rise in respiration is aresultof increase in the level of protein which will be expectedtoreduce the ATP/ADP ratio.
4. Over the climacteric period,although rate of respiration andnet protein content both rise,R rises more rapidly than proteinand, subsequently, falls ata faster rate than P. It is suggestedthat this may be due tothe ‘new’ protein containinga higher proportionof enzyme(s) directly involved in respirationand leading, forexample, to a reduction in the ATP/ADP ratio.

     

CHANGES IN RESTING POTENTIAL AND ION ABSORPTION INDUCED BY LIGHT IN A SINGLE PLANT CELL

1. Effect of light on ion absorption and resting potential of theinternodal cell of Nitella flexilis was investigated under variousconditions.
2. On illumination, the resting potential increasedby about 30mVin 10^–4 M KCl and by about 60 mV in 10^–4M NaClsolution. A similar photoelectric response was also observedin 10^–3 M KCl, 10^–2 M CaCl₂ and 5 x 10^–2 MCaCl₂ solutions, but not at all in 10^–2 M KCl solution.
3. Absorption of ions by the cell took place in parallel withthelight-induced change in resting potential.
4. Red and bluelights were very effective in increasing the restingpotential,while green light was almost ineffective. These differenteffectsof color lights were in good agreement with their effectsinincreasing the osmotic value of the cell.
5. The photoelectricresponse was not affected by phenylurethane,which, on the otherhand, strongly inhibited the light-inducedion absorption.
6. Theuptake of ions by the cell from the external medium intothevacuole is assumed to proceed in two different steps: thefirstis the process involving the ion movements across theoutermostplasmalemma, and the second is that involved in thetransportof ions through the cytoplasmic layer and tonoplast.The formerprocess is considered to be influenced by the increasein restingpotential probably caused by the light absorbed bychlorophyll.The process was, however, suggested to be independentof photosynthesis.On the other hand, the latter process issupposed to be relatedto photosynthesis. A discussion was madealong this line.

(Received July 26, 1962; )     

Superoxide dictates the mode of U937 cell ascorbic acid uptake and prevents the enhancing effects of the vitamin to otherwise nontoxic levels of reactive oxygen/nitrogen species

Exposure of U937 cells to low micromolar levels of ascorbic acid or dehydroascorbic acid, while resulting in identical ascorbic acid accumulation, is unexpectedly associated with remarkably different responses to exogenous oxidants. We observed that otherwise nontoxic levels of hydrogen peroxide, tert-butylhydroperoxide or peroxynitrite promote toxicity in cells preloaded with ascorbic acid, whereas hardly any effect was detected in cells pretreated with dehydroascorbic acid. Further experiments performed with peroxynitrite in cells preloaded with ascorbic acid provided evidence for a very rapid nonapoptotic death, preceded by early Bax mitochondrial translocation and by mitochondrial permeability transition. The notion that conversion of extracellular ascorbic acid to dehydroascorbic acid prevents the enhancing effects on oxidant toxicity and nevertheless preserves the net amount of vitamin C accumulated was also established using ascorbate oxidase as well as various sources of superoxide, namely, xanthine/xanthine oxidase or ATP-driven NADPH oxidase activation. These findings suggest that superoxide-dependent conversion of extracellular ascorbic acid to dehydroascorbic acid represents an important component of the overall survival strategy of some cell types to reactive oxygen/nitrogen species.     

SPECTRAL CHANGE OF LIGHT WITH DEPTH IN SOME LAKES AND ITS SIGNIFICANCE TO THE PHOTOSYNTHESIS OF PHYTOPLANKTON

1. A linear relation was found between the relative light intensityat 5 in depth and the mean chlorophyll a content of the euphoticzone, when they were plotted on logarithmic scales. The intensitiesof underwater lights of different wave lengths were measuredby a photocell with various colored filters. It was recognizedthat with the increase in chlorophyll a content the proportionof blue light fraction became reduced and that of red lightincreased. A similar relation was also found in the sea.
2. Thephotosynthetic rate.light relation was investigated withthesuspension of cultured Chlorella and Tabellaria. At lowlightintensities, the photosynthetic rate for red light waslargerthan those for blue and green lights. The photosyntheticrateunder the mixed light of red and blue was equal to thesum ofthe rates in the individual lights, so far as the intensityof each light was low. But when the intensity of red light wassufficiently high, the addition of blue light brought no furtherincrease in photosynthesis.
3. The photosynthetic rate-depthrelations were investigated bythe surface and underwater exposuremethods. Good agreementswere found between the results obtainedby these two differentmethods. However, there are some discrepanciesbetween the resultsof in situ exposure experiments and thoseobtained by the twomethods.

(Received January 11, 1963; )     

Light-induced changes in the fluorescence yield of chlorophyll a in Anacystis nidulans II. The fast changes and the effect of photosynthetic inhibitors on both the fast and slow fluorescence induction

1. The intensity dependence and spectral variations during thefast transient of chlorophyll a (Chl a) fluorescence have beenanalyzed in the blue-green alga Anacystis nidulans. (Unlikethe case of eukaryotic unicellular green or red algae, the fastfluorescence induction characteristics of the prokaryotic blue-greenalgae had not been documented before.)
2. Dark adapted cellsof Anacystis exhibit two types of fluctuationsin the fluorescenceyield when excited with bright orange light(absorbed mainlyin phycocyanin). The first kinetic patterncalled the fast (sec)fluorescence transient exhibits a characteristicoriginal levelO, intermediary hump I, a pronounced dip D, peakP and a transitorysmall decline to a quasi steady state S.After attaining S,fluorescence yield slowly rises to a maximumlevel M. From M,the decline in fluorescence yield to a terminalT level is extremelyslow as shown earlier by Papageorgiou andGovindjee (8). Ascompared with green and red algae, blue-greenalgae seem tohave a small PS decline and a very characteristicslow SM rise,with a M level much higher than the peak P.
3. A prolonged darkadaptation and relatively high intensity ofexciting illuminationare required to evoke DPS type yield fluctuationsin Anacystis.At low to moderate intensities of exciting light,the time forthe development of P depends on light doses, butfor M, thisremains constant at these intensities.
4. Fluorescence emissionwas heterogeneous during the inductionperiod in Anacystis;the P and the M levels were relativelyenriched in short-wavelengthsystem II Chi a emission as comparedto D and S levels.
5. Thefast DPS transient was found to be affected by electrontransportcofactor (methyl viologen), and inhibitors (e.g.,DCMU, NH₂OH)in a manner suggesting that these changes are mostlyrelatedto the oxido-reduction level of intermediates betweenthe twophotosystems. On the other hand, the slow SM changesin fluorescenceyield, as reported earlier (5, 15), paralleloxygen evolution.These changes were found to be resistant toa variety of electrontransport inhibitors (O-phenanthroline,HOQNO, salicylaldoxime,DCMU, NH₂OH and Antimycin a). It issuggested that, in Anacystis,even in the presence of so-calledinhibitors of cyclic electronflow, a "high energy state" isstill produced.
6. Measurementsof Chlorophyll a fluorescence and delayed lightemission inthe presence of both DCMU and NH₂OH indicate thatthe slow SMchanges are not due to the recovery of the reactioncenter IIin darkness preceeding illumination.
7. Our results, thus, suggestthat in Anacystis a net electrontransport supported oxidation-reductionstate of the quencherQ regulates only partially the developmentof the DPS transient,but the development of the slow fluorescenceyield changes seemsnot to be regulated by these reactions.It appears, from datapresented elsewhere, that the slow risein the yield resultsdue to a structural modification of thethylakoid membrane.

¹We are grateful to the National Science Foundation for financialsupport. (Received November 21, 1972; )     

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.     

STUDIES ON CHLOROPHYLLASE OF CHLORELLA PROTOTHECOIDESI. ENZYMATIC PHYTYLATION OF METHYL CHLOROPHYLLIDE

1. The relation between chlorophyll content and the hydrolyticactivity of chlorophyllase in Chlorella protothecoides was examined.An increase in the activity was parallel to that in chlorophyllcontent during the development of green colouration, or greeningcourse, in the bleached cells. The activity sharply declinedand a parallel disappearance of chlorophyll was also found duringbleaching of the green cells.
2. A partially purified water-solublepreparation of chlorophyllasewas obtained by n-butanol treatmentand fractionation with coldacetone. It showed high activityand hydrolyzed 2 mg chlorophylla per hr per mg protein.
3. Forseparation and identification of the pigments concernedin thechlorophyllase reaction, a new solvent system of paperchromatographywas introduced.
4. When methyl chlorophyllide a and phytol wereincubated withthe enzyme, two products were formed. By comparisonwith theRf values of isolated pure substances, one was identifiedaschorophyll a and the other as chlorophyllide a. This enzymedid not catalyze the phytylation of free chlorophyllide a, butit had the ability to attach phytol to methyl chlorophyllidea. The final step in the biosynthesis of chlorophyll a is brieflydiscussed.

¹ Contribution No. 158 from the Department of Biology, Facultyof Science, Kyushu University. Supported in part by a grant-in-aidfor Fundamental Scientific Research from the Ministry of Education.     

DE- AND RE-GENERATION OF CHLOROPLASTS IN THE CELLS OF CHLORELLA PROTOTHECOIDES: V. DEGENERATION OF CHLOROPLASTS INDUCED BY DIFFERENT CARBON SOURCES, AND EFFECTS OF SOME ANTIMETABOLITES UPON THE PROCESS INDUCED BY GLUCOSE

1. The green cells of Chlorella protothecoides were bleached todifferent extents when incubated (in the dark) in the nitrogen-freemedia containing, besides basal mineral nutrients, glucose,fructose, galactose, glycerol or acetate. Glucose and fructosewere found to have the strongest bleaching effect. Additionof a nitrogen source (urea) caused a considerable reductionof the bleaching. It was assumed that from the different carbonsources a certain common intermediate(s) causing the bleachingis formed, and that in the presence of the nitrogen source thesubstance is removed by reacting with it.
2. Using glucose asbleach-inducing agent, the effects of someantimetabolites uponthe processes of bleaching, division andgrowth of green algalcells were investigated, and it was demonstratedthat the processof bleaching occurs without being accompaniedby growth anddivision of the algal cells.
3. It was found that during theprocess of bleaching no net increasesin RNA and protein tookplace.

(Received March 11, 1965; )     

Studies on the destruction of indole-3-acetic acid by a species of Arthrobacter II. Properties of the oxidation system

1. Some properties of the IAA-oxidizing activity of lyophilizedcells of Artkrobacter sp. were examined.
2. 1. IAA oxidationseems not to be catalysed by peroxidase, polyphenoloxidase,laccase or dehydrogenase, but by an oxidase systemdifferentfrom the one reported earlier.
3. 2. The optimal pH for the oxidizingsystem is ca. 6.0, and thesystem is comparatively stable atpH 5 to 10.
4. 3. The optimal substrate (IAA) level is 10^–3M.
5. 4. Activity is inhibited by metal-chelating reagents, suchassodium azide, potassium cyanide, sodium diethyldithiocarbamate,potassium xanthogenate and 8-hydroxyquinoline, and sulfhydrylreagents, such as iodoacetamide, monofluoroacetic acid, p-chloromercuribenzoate,isatin, ß-naphthoquinone and ß-naphthoquinone-4-sulfonate.Hydroxybenzoic acid, sulfosalicylic acid and 2,4-dichlorophenolare also inhibitory.
6. 5. None of the IAA analogs tested (indole,skatole, 2,3-dihydroxyindole,indole-3-aldehyde, -3-carboxylicacid, -3-propionic acid, -3-lacticacid, -3-butyric acid, 5-hydroxyindole-3-aceticacid and D,L-tryptophan) are oxidized by the cells, and someanalogs (indole-3-carboxylicacid, -3-propionic acid, -3-butyricacid, 5-hydroxyindole-3-aceticacid, naphthalene-acetic acidand 2,4-D) are inhibitory at comparativelyhigh concentrations.
7. 6. The oxidizing activity is not stimulated by Mn⁺⁺ and isinhibitedby Co⁺⁺, Cu⁺⁺ and Hg⁺⁺.
8. 7. The oxidizing activitydisappears completely within 6 hrat 30, but is kept unchangedat least for two weeks at –20.

(Received August 7, 1967; )     

Formation of Tartaric Acid in Vitaceous Plants: Relative Contributions of L-Ascorbic Acid-inclusive and -noninclusive Pathways

The biosynthetic conversion of D-glucose to tartaric acid (TA)was studied in attached leaves and berries of Vitis labruscacv. Delaware (grape), and in leaves of Parthenocissus quinquefoliaL. (Virginia creeper) under light or dark conditions. D-[2-¹⁴C,3-³H]glucose was supplied for a period of 12 h and the ratioof ³H to ¹⁴C in cell wall-derived glucosyl units and TA wasexamined. TA produced via L-ascorbic acid (AA) should lose 3Hduring this conversion while TA produced via D-gluconate shouldretain ³H. In the light, approximately 85 to 91% of the TA presentin grapes and 98% of the TA present in Virginia creeper appearedto be generated via the pathway that involves AA. In the dark,approximately 69 to 74% of the TA in grapes and 87% of the TAin Virginia creeper was synthesized via the AA pathway. When0.5% unlabeled AA was present in the solution of labeled D-glucosethat was supplied to attached leaves of Virginia creeper, agreater proportion of TA was produced via the non-AA pathway.Similarly, detached Virginia creeper leaves produced a greaterproportion of TA via the non-AA pathway. These studies indicatethat vitaceous plants utilize the AA-inclusive pathway to producea major portion of their TA, especially in the light. The valueof P. quinquefolia as a useful model for year-round study ofthe biosynthesis of AA and TA is also discussed. (Received January 23, 1989; Accepted June 19, 1989)     

The Assimilation of Nitrogen from Ammonium Salts and Nitrate by Fungi

1. The assimilation of inorganic nitrogen by Scopulariopsis brevicaulisand some physiologically similar species has been studied. Theirfailure to assimilate completely from ammonium sulphate hasbeen shown to be due to the fall in pH of the medium inducedby the initial uptake of ammonia.
2. Complete assimilation ofammonia takes place in the presenceof the neutral salts ofeach of thirteen organic acids investigated.The organic acidsact primarily through their buffering effectwhich preventsor slows down the fall in pH. They are not specificallyrequiredfor ammonia assimilation by these fungi and can beeffectivelyreplaced by certain inorganic buffers.
3. The influence of severalexternal factors on the rate of assimilationof ammonia, nitrate,and nitrite has been studied in S. brevicaulis.In correspondingconditions the mycelium assimilates ammoniamore rapidly thannitrate over a wide range of conditions.
4. Ammonia, even invery low concentration, completely suppressesnitrate assimilationwhen both sources of nitrogen are presenttogether. Nitrite,however, is assimilated simultaneously withammonia. It is thereforeconcluded that ammonia blocks the reductionof nitrate to nitriteby the fungus.
5. The suppression of nitrate assimilation inthe presence of ammoniais common to many mould fungi besidesS. brevicaulis, and isbelieved to have adaptive significancein natural habitats.
6. The nitrate-reducing and assimilatingsystem is formed, evenwhen S. brevicaulis is grown in completeabsence of nitrate(ammonia medium with organic acid). It comesinto action rapidlywhen the inhibiting effect of ammonia isremoved. Similarly,nitrate-grown mycelium is capable of assimilatingammonia atmaximal rate without any adaptive lag.

     

Studies on Plant Growth Hormones: II. FURTHER BIOLOGICAL PROPERTIES OF 3-INDOLYLACETONITRILE

1. 3-Indolylacetonitrile is more active than 3-indolylacetic acidin the Avena straight-growth test, but less active in the Avenacurvature test at comparable concentrations. Reasons for thisare discussed, and results of previous work on plant extractsusing the curvature test as a means of assay are considered.
2. Transport of both the acid and the nitrile is polar, fromapexto base of the coleoptile. The nitrile can reach the growingcells as easily, and possibly more easily, than the acid. Thesignificance of these findings for a theory on the mechanismof action of the nitrile is discussed.
3. The nitrile is inactivein the pea curvature test and straight-growthof pea stem sectionsexcept at high concentrations. It is alsoinactive or only slightlyactive in lateral bud inhibition,root initiation, and petioleabscission at the concentrationstested.
4. It is less activethan the acid in root inhibition in cress,but approximatelyas active in Avena. It is approximately asactive as the acidin parthenocarpic fruit development, andinitiation of cambialactivity.
5. The significance of these results is discussed.

     

INHIBITION OF THE PHOTOSYNTHETIC CARBON DIOXIDE FIXATION OF GREEN PLANTS BY {alpha}-HYDROXYSULFONATES, AND ITS EFFECTS ON THE ASSIMILATION PRODUCTS

1. Several kinds of a-hydroxysulfonates, the bisulfite additioncompounds of aldehydes and ketones, were found to inhibit thephotosynthetic carbon dioxide fixation of the barley and wheatseedlings, tobacco leaf and Chlorella cells. Bisulfite additioncompounds of glyoxal, glyoxylate and benzaldehyde were moreeffective in this respect than those of formaldehyde and acetaldehyde.
2. The presence of -hydroxysulfonate causes an increase in ratiosof :¹⁴CO₂ incorporated in glycolate and alanine, and a decreasein incorporation in serine, malate, isocitrate and citrate.It was inferred that these changes are caused by the blockingof the formation of glyoxylate through inhibition of glycolicacid oxidase by the poison.
3. A reaction scheme was proposedto account for the above-statedresults, and the bearing ofthese findings on the possible roleof glycolic acid oxidasein the photosynthetic carbon dioxidefixation and in the formationof amino and organic acids wasdiscussed.

(Received December 8, 1961; )     

Studies on Plant Growth Hormones: I. BIOLOGICAL ACTIVITIES OF 3-INDOLYLACETALDEHYDE AND 3-INDOLYLACETONITRILE

1. Two neutral plant hormones, one isolated recently from plants(3-indolylacetonitrile) and the other (3-indolylacetaldehyde)reported to be present in plants, are avaible as pure syntheticcompounds for investigation of their biological activities.This paper is mainly concerned with their effects on cellelongationin the Avena coleoptile
2. 3-Indolylacetaldehyde is considerablyless active than 3-indolylaceticacid in the Avena straight-growthtest; for example, a 1.0 mg./l.solution of the aldehyde showsan activity equivalent to thatof a 0.1 mg./l. solution of theacid
3. An acidic substance is produced in solutions of the aldehydeduring the period of assay. In some experiments it accountsfor all of the activity shown by the aldehyde solutions, onthe assumption that it is 3-indoylacetic acid, and in otherexperiments it shows a greater activity than that of the aldehydesolutions from which it was obtained. Therefore, it is concludedthat 3-indolylacetaldehyde, itself is either inactive or inhibitory.Acid production in aldehyde solutions in vitro is much lower,a fact which suggests that there is enzymatic oxidation of aldehydeto acid in the presence of coleoptiles.
4. The activities of3-indolylacetaldehyde in the pea test andin root-inhibitionand of 3-indolylacetone in the straight-growthtest are brieflyreported.
5. 3-Indolylacetonitrile is considerably more activethan 3-indolylaceaticacid in the Avena straight-growth test;for erample, a 0.1 mg./l.solution of the nitrile shows an activityequivalent to a 1.0mg./l. solution of the acid. The inhibitoryeffect at concentrationsabove 1.0–10.0 mg./l. is lesswith the nitrile than withthe acid.
6. There is negligible productionof acid in solutions of the nitrileboth in vitro and in thepresence of Avena coleoptiles at temperaturesranging from –18?to 25? C. for varying lengths of time.The possibility of enzymaticconvesion of nitrile to acid insidethe cells of the coleoptileis discussed
7. The activities of 3-indolylacetamide and of 2:4-dichlorophenoxyaceticacid and the corresponding nitrile are considered in this connexion
8. The nitrile is destroyed by treatment with alkali but notbyacid. In the light of these results, it is desirable to re-examineprevious work on identification of auxins in plants by theiracid and alkali sensitivity. Evidence for the existence of thenitrile in a number of other plants is presented.

     

Leaf Nucleic Acids:: II. METABOLISM DURING SENESCENCE AND THE EFFECT OF KINETIN

The nucleic acids in the green and in the senescent leaves ofthree types of plant have been studied. High and low molecularweight RNA of the chloroplast is not present in senescent leavesof Xanthium pensylvanicum, but both cytoplasmic and chloroplasticfractions are found in yellow leaves of Vicia faba and Nicotianatabacum. RNA is more rapidly degraded than DNA in the leavesof these plants when they are detached, and kinetin treatmenttemporarily arrests the loss of chlorophyll and nucleic acid.Once X. pensylvanicum leaves are yellow and senescent they cannotbe re-greened, whereas those of Nicotiana spp., and to someextent those of V. faba, can be rejuvenated. We suggest thatthe retention of chloroplast RNA in yellow leaves may be a majorfactor determining their ability to re-green and that the patternof organelle senescence prior to the first stages of leaf autolysisand dehydration is species-specific.     

PRODUCTION OF YEAST VARIANTS BY AUXIN AND EFFECTS OF PLANT GROWTH REGULATORS ON THESE VARIANTS

Using diploid strains of Saccharomyces cerevisiae and S. ellipsoideus,the following facts were found:

1. Indole-3-acetic acid, 2,4-dichlorophenoxyacetic acid and -naphthaleneaceticacid produced stable variants differing in the cell form andin the response to the actions of auxin to elongate cells, toinduce respiration- deficient mutation and to promote sporulation.
2. The auxins also produced stable variants differing in theabilityto form spores.
3. Acetic acid had no above-menthionedactions of auxin.
4. Spore-formation and cell elongation of someof auxin-inducedvariants were controlled by auxin.

Biological significance of the auxin-induced variation is discussedand the usefulness of some of these variants as experimentalmaterial for auxin physiology in general is pointed out. (Received November 1, 1966; )