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.

     

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.

     

Aspects of Morphogenesis in a Dorsiventral Fern, Pteridium aquilinum (L.) Kuhn: With one Plate and ten Figures in the Text

The formation of the horizontal dorsiventral rhizome of Pteridiumaquilinum from the erect radial axis of the young sporelingis described. The shoot apex and the inception of leaves andbuds at the apical meristem have been investigated, and theirinception is shown to be essentially similar in long and shortshoots, later differences being due to differing rates of growthand internodal elongation in the two types of shoot.     

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.

     

Apical Dominance Control in Ipomoea nil: The Influence of the Shoot Apex, Leaves and Stem

The outgrowth of lateral buds is known to be controlled by theupper shoot tissues, which include the apex, the young leavesand the upper stem. An analysis of the influence of these plantparts on axillary bud elongation in Ipomoea nil was carriedout by various treatments on these specific tissues. A restriction of elongation in the main shoot due to eitherdecapitation or shoot inversion resulted in the release of apicaldominance A non-linear type of compensating growth relationshipwas observed between the 13 cm apical growing region of thestem and the lateral buds. It was determined by decapitation,defoliation and AgNO₃ treatments that both the 13 cm stem-growthregion and the young leaves (1–5 cm in length) had a muchgreater inhibitory influence on the outgrowth of specified lateralbuds than did the stem apex (consisting of the terminal 0.5cm of the shoot). The specified lateral buds which were analyzedfor outgrowth were located a number of nodes below the shootapex. The intervening nodes were debudded. Although the importanceof young leaves in the control of apical dominance has beenpreviously recognized, the most significant result from thepresent study with Ipomoea was the strong influence of the 13cm apical growth region of the stem on the out growth of thelateral buds. Apical dominance, Ipomoea nil L., Pharbitis nil, growth region, lateral bud outgrowth, decapitation, defoliation, shoot inversion     

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; )     

FLAVOPROTEINS IN THE LEAVES OF HIGHER PLANTS CATALYZING THE OXIDATION OF L-GLUTAMATE

1. Two forms of enzyme capable of catalyzing the oxidation of L-glutamate(and L-aspartate) were isolated from the leaves of spinach andseparated from each other by column-chromatographic purificationon calcium phosphate and anion exchangers. They were distinguishedas GD₁ (L-glutamate dehydrogenase 1) and GD₂ (L-glutamate dehydrogenase2). The purification procedures and some fundamental propertiesof the partially purified enzymes were investigated.
2. It wasdiscovered that the enzymes did not require any cofactor,ie., neither dialysis nor precipitation with ammonium sulfatecaused a fall in enzyme activities and the addition of DPN andTPN to the reaction mixture did not accelerate the reactionrate
3. From the results of spectroscopic investigation GD₁ andGD₂were shown to be flavoproteins, although their prostheticgrouphas not yet been identified The activity of GD₁ was enhancedby the addition of FAD or FMN, while GD₂ was not acceleratedby these factors.
4. The characteristics of the two enzymes includingsubstrate specificity,MICHAELIS constant, optimum pH of thereaction and specificityfor electron acceptors were compared.
5. From the stoichiometric study of the oxidation of L-glutamatewith these enzymes, it was confirmed that the reaction is representedby the following equation: L-glutamate+oxidized dye+h₂o
6. Among various inhibitors tested,molecular oxygen which couldfunction as electron acceptor ofL-glutamate oxidation in thepresence of GD₁ was found to causea strong inhibition uponthe same reaction with TTC as el acceptor.The inhibition wasconfirmed to be due to hydrogen peroxideproduced as a resultof the aerobic oxidation of L-glutamate.

(Received July 25, 1962; )     

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.

     

REDUCTION OF DEHYDRO-L-ASCORBIC ACID IN GREEN LEAVES

1. The capacity of green leaves for absorbing and converting substancesrelated to L-ascorbic acid was investigated, using detachedleaves of various plants, including soybean, pea, barley andspinach.
2. The greater portion of the absorbed dehydroascorbicacid wasrecovered in the leaves as ascorbic acid, minor portionsbeingdiscovered as dehydroascorbic acid and 2,3-diketogulonicacid. The recovery was about 60% of the absorbed dehydro ascorbicacid, in the cases of detached soybean and barley leaves, forinstance, thus suggesting the instability of the substance invivo.
3. The absorption and conversion of ascorbic acid and 2,3-di-ketogulonic acid in detached green leaves were also investigated.Most of the absorbed ascorbic acid reappeared in the leaves.On the other hand, no evidence for the conversion of 2,3-diketogulonicacid into ascorbic and dehydroascorbic acids was observed. Thegreater portion of the absorbed 2, 3-diketogulonic acid seemsto be decomposed in the leaves, under the condition of the presentstudy.

(Received April 17, 1961; )     

LACTATE AND GLUCOSE OXIDATION SYSTEMS IN ACETOBACTER SUBOXYDANS

1. From a strain of Acetobacter suboxydans, a glucose and a lacticenzyme were obtained in cell-free states. The lactic enzymeshows as strong activity as the glucose enzyme but is more stablethan the latter toward various purification procedures: bothare sensitive to high temperature treatment. Activities of thetwo enzymes and the MICHAELIS constants of the glucose enzymewere determined under both aerobic and anaerobic conditions.
2. Carbon monoxide inhibits the oxygen-uptake in both glucoseandlactate oxidation. WARBURG's distribution constant for lactateoxidation is 6.7. These results suggest the participation ofan heme enzyme in the oxidation system.
3. Effects of copperreagents, narcotics and PCMB were also examined.
4. The dehydrogenaseactivities (reduction of dye) of the enzymesare more sensitiveto high temperature than the correspondingactivities in oxygen-uptake.
5. By combining a dehydrogenase preparation which has lost itsoxygen-absorbing activity through acetone treatment, with aheated extract, a partial recovery of oxygen-uptake can be realizedin lactate oxidation.
6. L-Cysteine is utilized as hydrogen donorby the bacterium. Thisoxidative reaction, unlike the oxidationof lactate, is notinhibited by surface active reagents.

(Received May 16, 1960; )     

STUDIES ON ALGAL CYTOCHROME: I. ENZYMIC ACTIVITIES PERTAINING TO PORPHYRA TENERA CYTOCHROME 553 IN CELL-FREE EXTRACTS

1. Enzymic activities pertaining to Porphyra tenera cytochrome553 were investigated with cell-free extracts of a red alga,Porphyra tenera, and various fractions prepared therefrom.
2. Thealgal extracts were found to be incapable, in the dark,of catalyzingoxidation of reduced cytochrome 553 at a ratesufficient toaccount for the respiratory oxygen-uptake in theintact cell.Oxidation of cytochrome 553 was highly acceleratedon illumination.The former reaction was found to be cyanide-sensitiveand thelatter, cyanide-insensitive. Both activities were foundto belocalized in the particulate fraction of the cell extract.
3. Significantactivities of reduced pyridine nucleotide-cytochromereductasewere discovered in the soluble fraction of the cellextract,the reaction being two or three times faster with TPNHthanwith DPNH as electron donor. There was no reaction withsuccinatein the presence of cytochrome and 2,6–dichlorophenolindophenol.
4. Porphyra tenera cytochrome 553 was shown to be localized inthe plastids of the algal cell.
5. Possible functions of cytochrome553 in the algal metabolismwere discussed.

     

WATER PERMEABILITY OF THE CELL WALL IN NITELLA

1. A method has been developed to measure the hydraulic conductivityof the wall of the internodal cell of Nitella flexilis.
2. Therate of water penetration through the cell wall varies linearlywith the hydrostatic pressure difference between the two sidesof the wall, showing that water permeability of the cell wallremains independent of the pressure difference applied.
3. Waterpermeability of the cell wall is inversely proportionalto itsthickness It is 30µµmin^–3{dot}atm^–3when the thickness of the wall is 10 µ.
4. Water permeabilityof the cell wall is the same for inward andoutward water flow.The polar water permeability of the entiremembrane system (walland protoplasmic part) of the living celldemonstrated by KAMIYAand TAZAWA (1) is, therefore, due tothe living protoplasmicpart.
5. The ratio of the inward to outward permeability constantsofthe protoplasmic layer alone is higher than that of the entiremembrane system composed of protoplasmic layer and cell wall.

¹ Dedicated to Prof. H. TAMIYA on the occasion of his 60th birthday.The present work was supported in part by a Grant-in-Aid forFundamental Scientific Research from the Ministry of Education. ² Present address: Sh?in Women's College, Kobe. (Received July 21, 1962; )     

COMPONENTS OF THE ELECTRON-TRANSFERRING SYSTEM IN ACETOBACTER SUBOXYDANS AND RECONSTRUCTION OF THE LACTATE OXIDATION SYSTEM

1. Cytochromes a₁⁵⁹⁰, b⁵⁶⁰, c₁⁵⁵⁴ and c₁⁵⁵² were isolated andpurifiedfrom a strain of Acetobacter suboxydans. The proceduresusedwere described in detail.
2. The main cytochrome band at550-560 mµ in intact cellssplitted at liquid air temperatureinto two bands, 551 mµ(strong) and 559 mµ (weak).
3. Optical and physiological properties of the four cytochromeswere investigated. Lactic dehydrogenase activity was found tobe associated with cytochrome c₁⁵⁵⁴. The two c₁-type cytochromes,especially cytochrome c₁⁵⁵⁴, persisted in their reduced formafter the purification through many steps.
4. By some combinationsof isolated components reconstruction ofthe oxygen uptake systemcould be realized.
5. The oxygen-consuming activity of purifiedoxidase preparationswas accelerated by a-tocopherol but notby Emasoll 4130 andTween 80.
6. Some discussions were made onthe nature of terminal oxidase,the role of cytochrome c₁⁵⁵²in the electron-transport system,and persistence of reducedstate of c₁-type cytochromes.
7. A possible scheme of the electron-transferringsystem of Acetobactersuboxydans was presented.

(Received May 16, 1960; )     

The 'Diffuse' Centromere or Polycentric Chromosomes in Spirogyra

1. Among ten species of Spirogyra types are distinguished withlarge-, medium-, and small-sized chromosomes.
2. Evidence ofcompound structure is presented with regard to thelarge-andmedium-sized chromosomes.
3. Parallel separation of chromatids,first described by Geitlerfor S. crassa, is found in all specieshaving large chromosomesand to some degree in those with medium-sizedchromosomes.
4. It is suggested that the parallel separationof chromatids iscaused by their polycentric nature.
5. Polyploidyin the genus is only doubtfully comparable with thatin thehigher plants.
6. It is suggested that in Spirogyra the localizedcentromere mayhave evolved in a polycentric chromosome.
7. Comparisonsare drawn between Spirogyra and other organismsstated to have‘diffuse’ centromeres and it is suggestedthat theirchromosomes also are polycentric.

     

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.

     

STUDIES ON THE MECHANISM OF GROWTH INHIBITING EFFECT OF LIGHT

1. A substance which inhibits indoleacetic acid (IAA)-and naphthaleneaceticacid (NAA)-induced elongation of Avena coleoptile section andIAA-induced Avena coleoptile curvature was found in an ethersoluble neutral fraction of water extract of sunflower leavesand in agar blocks containing the diffusate from young sunflowerleaves.
2. This substance also inhibits the growth of isolatedsunflowerepicotyl.
3. The R_f value (0.9) of the substance ona paper chromatogramdeveloped with ammoniacal iso-propanolindicates that it isidentical with the inhibitor reported byAUDUS et al. (1956),but not with inhibitor-ß.
4. Theinhibitor can be transported from leaf to stem, and thetransportseems to be accelerated by illuminating the leaf.
5. The auxindiffused from sunflower leaf into agar block may beidenticalwith IAA.
6. A substance, which has the same properties as theinhibitorfrom sunflower leaf, was obtained in crystalline formfrom theleaf of Jerusalem artichoke.
7. The mechanism of growthinhibition caused by this crystallinesubstance seems to involveinactivation of a sulfhydryl group.
8. The reason why the stemgrowth of sunflower seedlings is reducedby strong light isdiscussed: the amount of the inhibitor transportedfrom leafto stem is increased under strong light, and in thestem, growthinhibition is caused by a direct effect of thisinhibitor ongrowth and by its inhibiting effect on the transportof IAAfrom leaf to stem.

¹ Present address: Botanical Garden, Faculty of Science, Universityof Tokyo, Tokyo (Received February 15, 1961; )     

MODE OF ACTION OF MALEIC HYDRAZIDE ON THE GROWTH OF ESCHERICHIA COLI AND AVENA COLEOPTILE SECTIONS

1. MH was found to suppress the growth and respiration of E. colias well as the IAA-induced growth of Avena coleoptile sections.
2. These suppressions could be reversed more or less strikinglyby the addition of a trace of heavy metals such as Co, Mn, Ni,Zn, Cu, or Mo.
3. The reversal could also be achieved by cysteine,thioglycollate,or fumarate, the latter two substances being,however, lesseffective.
4. The inhibition of the growth of E.coli by MH was completelyrelieved by the addition of IAA. Conversely,the inhibitionof the microbial growth by high concentrationsof IAA couldbe relieved by the addition of MH.
5. It was inferredthat MH may block certain heavy metal-catalyzedprocess, inwhich some thiol substance and IAA are participating,probablyby combining with the heavy metal.

(Received June 23, 1960; )     

"GIGANTISM" OF CHLORELLA VULGARIS I. MECHANISM OF INDUCTION OF CIGANTISM

1. Based on the microscopic observations, two stages, "giant cellstage" and the subsequent "palmelloid body stage", were distinguishedin the process of formation of giant Chlorella induced by theaddition of sugars. The "giant cell" is much larger in sizethan the control cell, but the other morphological featuresare the same as those of the latter. The "palmelloid body" isa form composed of many conjoined autospores.
2. When a highconcentration of glucose was maintained in the medium,gigantismwas also maintained. Under this condition, the algashows acyclic transformation between "giant cell" and "palmelloidbody"without returning to the small single cells.
3. Large amountsof carbohydrate composed of hexose were foundto be accumulatedin the giant algal cells, and it was inferredthat this carbohydrateaccumulation causes greater enlargementof cell volume as comparedwith control cells.
4. Uronic acids, which were found to be absentin the control cells,were formed and lost in the cells culturedin the glucose mediumin parallel with the appearance and disappearanceof gigantism.
5. Pectic substances, from which uronic acids areconsidered tobe derived during the extraction procedure, werefound to bepresent only in giant Chlorella.
6. The conjoinedautospores in giant Chlorella (at the palmelloidbody stage)were separated to some extent by the addition ofEDTA, and theresulting cells were similar to control Chlorellacells.
7. Basedon these results it was inferred that inductive formationofthe pectic substances is causally related with the appearanceof "palmelloid body".

¹ Present address: Department of Chemistry, College of GeneralEducation, Osaka University, Toyonaka, Osaka.     

A METABOLIC PATHWAY OF ISOCITRIC ACID IN COTYLEDONS OF A BEAN, VIGNA SESQUIPEDALIS

1. It has been established that the absence of isocitric dehydrogenaseactivity in cotyledons of Vigna sesquipedalisin the germinationstage is due to the lack of endogenous TPN. It is unlikely thatthe TCA cycle in the cotyledon is operative.
2. The activitiesof enzymes of the glyoxylate cycle, a modifiedTCA cycle, weremeasured through the germination stage. Theiractivities wereconsiderably higher in the cotyledon tissuethan in the hypocotyl.A dominant metabolic pathway of isocitricacid in the cotyledonmay be the glyoxylate cycle.
3. DPN kinase which produces TPNfrom DPN, ATP and Mg⁺⁺ was localizedin the supernatant portionof cell components in the cotyledon.Its activity was low. DPNkinase serves as a control factorfor the cotyledon metabolism.

(Received April 17, 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.