The Effect of Selected Growth-Promoting and Growth-Inhibiting Substances on the Extension of Segments of Etiolated Tomato Seedling Hypocotyls

The effects of a number of growth-promoting and growth-inhibitingsubstances, including two fungal toxins, were studied on theextension of segments of etiolated tomato seedling hypocotyls.The bioassay was sensitive to small quantities of NaF, coumarinand ₂, ₄-DNP and inhibition was observed at all concentrations.₂, ₄-DNP or Iodoacetate stimulated growth at concentrationsbetween 1? 10^–4 and 5 ? 10^–6M. or 1 ? 10^–6and 1 ? 10^–7M. respectively. Inhibitor experiments inbuffered nutrient solution were approximately 10 per cent. moresensitive than those in deionized water. By means of paper partition chromatography small quantitiesof two fungal toxins, fusaric and alternaric acid were chromatographedand bioassayed. The effect of fussric acid (5, n-butyI picolinicacid) on hypocoty1 growth was detected at concentrations aslow as 1 ? 10^–5M. Experiments with recongnized growth-promoting substances showedthat Kinetin inhibited growth at concentrations up to 1 ?10^–8M.in both light and dark. IAA inhibited growth up to 1 ? 10^–6M.At 1 ? 10^–7 and 1 ? 10^–8 only small increases occurredwith IAA and the effect of light was negligible. Gibberellicacid (GA₂)stimulated growth at concentrations from 10^–3to 10^–7M. and significant increases up to 17 per cent.were recorded in the light. Since the light induced inhibitionwas only partly restored, the existence of some other naturallight sensitive growth substance is suggested. The value ofthe bioassay as a method for estimating natural growth-inhibitingand growth-promoting substances is discussed.     

Light-induced changes in membrane potential in Spirogyra

Spirogyra cells exhibited changes in membrane potential whenthey were exposed to light. Cells made chloroplast-free didnot show any light-induced potential change (LPC) upon illuminationwith white light and also monochromatic red (680 nm) and farred (720 nm) light. LPC was observed when the cell containedonly a small fragment of chloroplast, whether the cell had anucleus or not. The magnitude of LPC depended on the amountof chloroplast in the cell. DCMU at 10^–5 M, CCCP at 10^–5 M and DNP at 10^–4M at pH 5.5 suppressed LPC, while CCCP at 1–5 ? 10^–6M, NH₄Cl at 5 ? 10^–2 M and DNP at 10^–4 M at pH 7.0stimulated LPC. PMS at 10^–4 M stimulated LPC and couldinduce LPC which was completely inhibited by DCMU. These factssuggest that LPC is related to noncyclic and cyclic electronflows. The influences of light and dark conditions and various metabolicinhibitors (DCMU, DNP, CCCP, NH₄Cl) on ATP level have been investigated.No significant difference in the ATP level was observed betweencells in the light and dark. DNP at 10^–4 M (pH 5.5) andCCCP at 5 ? 10^–6 M decreased the ATP level significantly,while DCMU and NH₄Cl only slightly. Good correlation was notfound between the total ATP level and LPC in Spirogyra. LPC occurred even when the external medium contained only asingle salt such as KCl, NaCl or CaSO₄. LPC was also recorded in chloroplasts in situ and in vitro.The mode of LPC of chloroplasts was quite different from thatof the cell. On illumination, the chloroplast potential changedvery rapidly and transiently in the positive direction thenrecovered spontaneously to almost the original potential level. Possible causes of LPC are discussed in relation to the electrogenicion pump. ¹ Present address: Department of Botany, Faculty of Science,University of Tokyo, Hongo, Bunkyo, Tokyo 113, Japan. (Received November 9, 1977; )     

The NADP$-specific isocitrate dehydrogenase of Rhodospirillum rubrum

The NADP^$-specific isocitrate dehydrogenase was partially purifiedfrom photosynthetically-grown Rhodospirillum rubrum. The pHoptimum is between 7.5 and 9.0 in phosphate buffer. The apparentKm is 3.1x10^–5 M for isocitrate, 5.1x10^–5 M forNADP^$, 1.7x10^–5 M for manganese, 1.5x10^–4 M formagnesium, and 3.5x10^–3 M for inorganic orthophosphate.Arsenate exerts a slight inhibition. The Q₁₀ between 17.5°Cand 40°C is 1.62, and the energy of activation at 25°Cis 9.74 Kcal/mole. Glyoxylate and oxalacetate cause concertedinhibition of the enzyme activity. Various nucleotides inhibitthe activity. The kinetics of inhibition by ATP was found tobe mixed type with respect to NADP^$ and isocitrate, the K_i valuesbeing 1.17x10^–3 M and 1.10x10^–3 M respectively.The inhibition between ATP and orthophosphate is competitivewith a K_i of 10^–4M. Thiol binding reagents are inhibitory;this inhibition is reversed by cysteine or reduced glutathione. (Received October 1, 1971; )     

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

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

L-Leucine Transport in Isolated Protoplasts of Vinca Suspension Culture: Characterization of Uptake

The uptake of L-leucine into Vinca protoplasts was studied undervarious conditions. The uptake was highly pH-dependent, withthe optimal pH between 3.0 and 4.0. The uptake was also energydependent, since azide, 2,4-dinitrophenol (DNP), carbonyl cyanidem-chlorophenyl hydrazone (CCCP), and iodoacetate inhibited theuptake. Oligomycin, N,N'-dicycIohexyI carbodiimide (DCCD) andvanadate, but not ouabain, inhibited the uptake, suggestingthat ATPase for H⁺ electrogenic extrusion was necessary to theuptake of L-leucine. The uptake showed stereospecificity, butwas partially inhibited by other L-amino acids. A kinetic studyof the uptake showed that the uptake was multiphasic with threesaturable phases and one unsaturable phase which occurred atconcentrations of L-leucine over 1 mM. The K_m values of thethree affinity sites were 1.4 x 10^–3 M, 1.3 x 10^–4M, 4.3 x 10^–5 M; the maximum velocity values were 3.3x 10^–8, 4.5 x 10^–9, 1.8 x 10_–9 mol/10 min/4x 10⁶ cells. (Received April 18, 1981; Accepted August 25, 1981)     

Light dependency of the mating process in Closterium acerosum

Sexual cell division and activation of gametangial cells forconjugation in Closterium acerosum were induced by light. L₂₀₀cells conjugated at maximum level under the following conditions;(i) a light intensity higher than 1,000 lux in a 16-hr lightand 8-hr dark regime and (ii) an illumination time longer than12 hr at 3,000 lux. L₂₀₀ cells also conjugated under continuousillumination at 3,000 lux. The action spectrum for the activation of gametangial cellshad peaks around 450, 611 and 665 nm. 3-(4'-Chlorophenyl)-l,l-dimethylurea (CMU) inhibited the accumulationof carbohydrates and sexual cell division at 10^–5 M andthe activation of gametangial cells for conjugation at 10^–4M. (Received August 15, 1977; )     

Vessel element formation in cultured carrot-root phloem slices

The effects of light, auxin and cytokinin on vessel elementformation in phloem slices of carrot root were examined. When slices of carrot cultivars, ‘Nakamura-senko-futo’and ‘Yamada-hyakunichisenk6- naga’, preculturedin the dark on modified Murashige and Skoog's medium for twodays were cultured on a medium containing 5x10^–6 M 2,4-Din the dark, no vessel element formation occurred. When preculturedslices were cultured in the light with 5x10^–6M 2,4-D,vessel element formation was remarkable. But when 5x10^–7Mkinetin, benzyladenine or zeatin was added, vessel elementswere readily formed even in the dark. When slices were cultured in the light, a cytokinin-like substance(s)that causes vessel element formation was produced in the slices,then was released to the medium. The substance(s) was fairlystable to heat. In slices of carrot cultivars, kuroda-gosun, ‘Kintoki’and ‘Kokubu-senk6-6naga’, a different result forvessel element formation was obtained. When slices of thesecultivars were cultured on a medium containing 5x10^–6M2,4-D in the dark, vessel element formation was remarkable.It seemed, therefore, that these cultivars contain enough ofa cytokinin-like substance(s) to form vessel elements. In fact,vessel element forming activity was found in the alcohol extractof carrot root phloem from these cultivars. (Received June 8, 1971; )     

The Effect of L-Phenylalanine on Phenylalanine Ammonia-lyase and Cell Division in Artichoke Callus Culture

5 x 10^–5 M L-phenylalanine overcame the inhibitory effectof white light on cell division in artichoke callus culturesand increased extractable phenylalanine ammonia-lyase (PAL)activity compared to cultures grown in the presence of 5 x 10^–4M phenylalanine The lower concentration of the amino acid alsoenhanced rates of uptake and incorporation of ¹⁴C labelled phenylalaninethroughout G₁ and S. Differences between the two concentrationswere greatest during S with a 4-fold increase in uptake anda 3-fold increase in incorporation It is suggested thereforethat the capacity of 5 x10^–5 M phenylalanine to offsetthe light effect is due to an indirect stimulatory effect onamino acid and protein metabolism Increased levels of extractablePAL activity would then be reflected by this general stimulationof protein synthesis. Helianthus tuberosus L, Jerusalem artichoke, callus culture, cell division, phenylalanine ammonia-lyase     

Auxin-gibberellin relationships in. their effects on hypocotyl elongation of light-grown cucumber seedlings IV. Inhibition of IAA-induced elongation by N,N'-dicyclohexylcarbodiimide and its reversal by gibberellin A3

IAA-induced elongation and control growth of light-grown cucumberhypocotyl sections were markedly inhibited by DCCD, an inhibitorof membrane-bound ATPases. The concentration effective for inducingmarked inhibition was more than 10^–5 M. At 10^–5M DCCD, there was an apparent antagonism between IAA and DCCD.At 5 x 10^–5 M DCCD, the inhibition was partially recoveredby 10^–4 M of IAA. The results might indicate a close associationof the auxin action with membrane-bound ATPases. The DCCD inhibitionwas so strong that treatment with 10^–4 M DCCD for about5 min significantly suppressed further growth and longer incubationkilled the sections. In contrast, DCCD had not inhibitory effecton both control growth and IAA-induced elongation if GA₃ waspresent simultaneously. DCCD treatment followed by GA₃ treatmentstill resulted in the inhibition, suggesting that the inhibitionwas not reversible. In order to obtain reversal of DCCD inhibitionby GA₃ both compounds must be present at the same time. TheGA₃ effect is discussed in connection with the mechanism ofDCCD action on membrane-bound ATPases. (Received October 6, 1975; )     

Effects of disalicylidenepropandiamine and near far-red light on 14CO2-fixation in Chlorella cells

1) With Chlorella ellipsoidea cells, in the presence of 5x10^–6M DSPD, or in its absence, the amounts of ¹⁴CO₂ incorporatedin P-esters, serine-plus-glycine and alanine were larger underred light than under blue light, whereas blue light specificallyincreased ¹⁴CO₂-incorporation in aspartate, glutamate, malateand fumarate (blue light effect). The amount of total ¹⁴C fixedunder blue or red light was greatly decreased by the additionof DSPD. When the concentration of DSPD was raised to 5x10^–4M, practically no radioactivity was found, under blue or redlight, in aspartate, glutamate and fumarate. Radioactivity inalanine was greatly increased. Effects of higher concentrationof DSPD are explained as due to the inhibition of PEP carboxylaseactivity in Chlorella cells. 2) The percentage incorporation of ¹⁴C into aspartate and theother compounds mentioned above, under near infra-red illuminationwas significantly smaller than that under blue light and wasalmost equal to that under red light. These results along withthe effect of 5x10^–6 M DSPD, exclude the possibility thatcyclic photophosphorylation is involved in the "blue light effect"mechanism. (Received December 12, 1969; )     

Diurnal regulation of NO3- uptake in soybean plants I. Changes in NO3- influx, efflux, and N utilization in the plant during the day/night cycle

The effect of light on NO₃^– utilization was investigatedin non-nodulated soybean (Clycine max L. Merr., cv. Kingsoy)plants during a 14/10 h light/dark period at a constant temperatureof 26C. A 30–50% decrease of net NO₃^– uptake ratewas observed 2–6 h after the lights were turned off. Thiswas specifically due to an inhibition of NO₃^– influx asmeasured by ¹⁵N incorporation during 5 min. The absolute valuesof NO₃^– efflux depended on whether the labelling protocolinvolved manipulation of the plants or not, but were not affectedby illumination of the shoots. Darkness had an even more markedeffect in lowering the reduction of ¹⁵NO₃^– in both rootsand shoots, as well as xylem transport of ¹⁵NO₃^– and reduced¹⁵N. Concurrently with this slowing down of transport and metabolicprocesses, accumulations of NO₃^– and Asn were significantlystimulated in roots during the dark period. These data are discussedin view of the hypothesis that darkness adversely affects NO₃^–uptake through specific feedback control, in response to alterationsin the later steps of N utilization which are more directlydependent on light. Key words: Glycine max, light/dark cycles, nitrate uptake, nitrate reduction     

The occurrence and properties of dihydrofolate reductase in pea seedlings

Dihydrofolate reductase (E.C. 1.5.1.3 [EC] ) was found in pea seedlingsand was partially purified by treatments with ammonium sulfate,protamine sulfate and by DEAE-cellulose column chromatography.Some properties of the enzyme were investigated. Optimum pHfor the reaction was 6.5. In the enzyme reaction, FAH₂ and NADPH₂were specifically required. MICHAELIS constants for FAH₂ andNADPH₂ were 4.3x10^–6 M and 4.0x10^–5 M, respectively.Folate antagonists such as aminopterin, methotrexate and pyrimethaminewere potent inhibitors of this enzyme. Enzyme activity was almostcompletely inhibited at a concentration of 10^–7 M of aminopterinand methotrexate and 10^–6 M of pyrimethamine. Growth of germinating pea seeds was inhibited by aminopterin,methotrexate and pyrimethamine, and it recovered significantlywith a tetrahydro-derivative of folate, CF, but not with dihydrofolicor folic acid. These results suggest that growth inhibitionof pea seedlings by these antagonists is due to inhibition ofdihydrofolate reductase in seedlings. ¹Studies on the enzymatic synthesis and metabolism of folatecoenzymes in plants IV. (For the previous paper, Part III, seeReference (21)) . Part of this paper was presented at the AnnualMeeting of the Agricultural Chemical Society of Japan held atTokyo on April 4, 1967 (Received October 8, 1969; )     

O-Benzylhydroxylamine: An Inhibitor of Phenylpropanoid Metabolism in Plants

O-Benzylhydroxylamine (OBHA) is a potent inhibitor of phenylalanineammonialyase (PAL, EC 4.3.1.5 [EC] ) and phenylpropanoid metabolismas evidenced by its effects on three plant species [soybean(Glycine max (L.) Merr.), buckwheat (Fagopyrum esculentum Moench.),and mung bean (Vigna radiata L.)]. When supplied to roots, OBHA(10^–5 M) did not significantly inhibit light- or dark-growthof soybean seedlings, but reduced (25%) soluble hydroxyphenoliccompound accumulation in light-grown axes. Higher concentrations(510^–5 M) of OBHA caused reductions (25%) in axis freshweight of light-grown seedlings (72 h), but did not lower axisweight of dark-grown seedlings. Anthocyanin accumulation inhypocotyls of intact mung bean seedlings was reduced by 25%after 3 days light growth after treatment with OBHA (10^–5M) via root feeding. Anthocyanin content of excised, etiolatedbuckwheat hypocotyls floated on solutions of OBHA (10^–5M) and incubated in the light for 24 h was reduced by 40%. L-Phenylalanineand t-cinnamic acid, intermediates of phenylpropanoid metabolism,were able to partially reverse this inhibition in buckwheat.Extractable PAL activity (specific activity basis) in soybeanaxes was substantially reduced (20% in dark, 40% in light) asearly as 24 h after root feeding with OBHA (10^–5 M). Reductionof PAL activity (specific activity or per axis basis) by OBHAcompared to control levels, continued throughout a time courseof 96 h. Kinetic studies on soybean PAL revealed a K_m of 1.1mM for L-phenylalanine and an apparent K_i of 3.5 µM forOBHA. (Received May 31, 1985; Accepted August 6, 1985)     

Factors Influencing Alanine Aminotransferase Activity in Leaves of Lolium temulentumL.: II. EFFECTS OF GROWTH REGULATORS AND PROTEIN BIOSYNTHESIS INHIBITORS

Effects of kinetin (K), gibberellin A₃ (GA₃), and 2-(chloroethyl)-trimethylammoniumchloride (CCC) on levels of alanine aminotransferase (GPT) andrates of protein synthesis were studied with both intact plantsand isolated leaf segments of Lolium temulentum L. In intactplants CCC stimulated and CA₃ reduced GPT activity, the effectsbsing much greater in 8.h than in 16-h photoporiods. CCC showedmaximum stimulatory effects at 10^–2 M and K at 5 x 10⁵M. No effect of GA₃ could be demonstrated with concentrationsup to 10^–4M. Both K and CCC retarded GPT decline in leafsections, the latter without associated effects upon pigmentbreakdown. Cycloheximide was highly effective in reducing proteinsynthesis in leaf sections. A close correlation between rateof protein synthesis and GPT activity was found over an inhibitorconcentration range from 10^–6 to 10^–4 M. The resultsare discussed in terms of possible methods of in vivo regulationof GPT activity.     

Effects of Preillumination on Dark Nitrogen Fixation and Respiration by Anabaena Cylindrica

In whole filaments of Anabaena cylindrica dark nitrogen-fixingactivity (measured as acetylene reduction) and respiration increasedwith the light intensity of a fixed period of preillumination,saturating at ca. 10,000 lux. With saturating light during preillumination,the amount and duration of dark nitrogen-fixing activity increasedwith length of preillumination, but respiration declined rapidlyin the dark. At dark respiration rates below 250 nmol O₂ uptake mg protein^–1?h^–1(State 1) no significant nitrogen-fixing activity is observed.From 250 to 550 nmol O₂ uptake?mg protein^–1?h^–1(State 2), nitrogen-fixing activity depends on O₂ uptake whileabove 550 nmol O₂ uptake?mg protein^–1?h^–1 (State3), nitrogen-fixing activity no longer increases with furtherincrease in O₂ uptake rate. (Received June 18, 1983; Accepted November 10, 1983)     

Biological activity of phyllosinol, a phytotoxic compound isolated from a culture filtrate of Phyllosticta sp.

1. Phyllosinol is a phytotoxic metabolite of Phyllosticta sp. Thissubstance at 100 µg/ml produced dark grey necrotic lesionson the leaf of red clover. Sensitivities of various plant speciesto phyllosinol differed both quantitatively and qualitatively.
2. Phyllosinol reduced root growth in rice seedlings by 60% at10^–4 M, whereas stimulation of root elongation occurredat a concentration range from 10^–9 to 10^–5 M.
3. Phyllosinolat 2.5x10^–4M promoted adventitious root formationin epicotylsof Azukia cuttings by about 100%. Promotion waspartly reducedby simultaneous application of cysteine.
4. IAA-induced elongationof isolated Avena coleoptile sectionswas inhibited by phyllosinolat a concentration range from 10^–5to 10^–3M.
5. Sulfhydrylcompounds, i.e. cysteine and glutathione relievedinhibitioncaused by phyllosinol in IAA-induced elongation ofAvena coleoptilesections.
6. GA₃-induced elongation of wheat leaf sections wasslightly inhibitedby phyllosinol at 10^–4M.
7. Phyllosinolalso has antibiotic activity. Among the organismstested, Phycomycetesand Gram-negative bacteria appeared mostsusceptible to phyllosinol.

(Received April 21, 1970; )     

Selective inhibition of antimycin A-insensitive respiration in Ustilago maydis and Ceratocystis ulmi

Sporidia of Ustilago maydis and conidia of Ceratocystis ulmipossess an antimycin A and azide-tolerant electron transportpathway which apparently diverts electrons to O₂ from some pointon the substrate side of the antimycin A block. The alternatepathway (induced by 0.5 µg/ml antimycin A or 5x10^–4M sodium azide) supports a respiratory rate 1.5–2 timesthat of the normal system, but has a terminal oxidase with alower than normal affinity for O₂. A similarly high respiratoryrate in U. maydis is supported by the normal pathway when uncoupledby 4 µg/ml of 4,5-dichloro-2-trifluoromethylbenzimidazole,but a high affinity for O₂ in this case indicates that the normalterminal oxidase is utilized. Respiration by the normal pathway in both fungi is only slightlyor moderately inhibited by 1.5x10^–3 M benzohydroxamicacid (BHAM) and 5x10^–4 M 8-hydroxyquinoline. The alternatepathway in U. maydis, however, is inhibited as much as 84 and92% respectively by these two compounds, while alternate respirationin C. ulmi can be inhibited as much as 86 and 76% respectively.BHAM, 8-hydroxyquinoline, 2-pyridinethiol-1-oxide, a,a'-dipyridyl,carboxin, and diphenylamine inhibit alternate respiration ata site on the alternate pathway which is not part of the normalelectron transport system. Antimycin A and azide-insensitiverespiration found in U. maydis and C. ulmi closely resemblesinhibitor insensitivity noted in several fungi and some higherplants. Such an alternate respiratory pathway may be an earlystep in the evolution of oxidative phosphorylation. (Received June 27, 1972; )     

Effects of Abscisic Acid on the Growth Pattern of the Shoot Apical Meristem and on Flowering in Chenopodium rubrum L.

Abscisic acid (ABA) at 1 x 10^–4 M or 3 x 10^–4 Mwas applied to the apical buds of Chenopodium rubrum plantsexposed to different photoperiodic treatments and showing differentpatterns of floral differentiation. Stimulation of growth inwidth of the apical meristem of the shoot and/or inhibitionof growth in length was obtained under all photoperiodic treatments.This change of growth pattern was followed by different effectson flowering. In non-induced plants grown under continuous light ABA stimulatedpericlinal divisions in the peripheral zone and the initiationof leaves as well as the growth in width of bud primordia. Inplants induced by two short days reduced growth of the meristemcoincided with ABA application. Longitudinal growth of the meristemwas inhibited in this case and only a temporary stimulationof inflorescence formation took place. In plants induced ata very early stage, ABA exerted a strong inhibitory effect onflowering. A permanent and reproducible stimulatory effect onflowering was obtained in plants induced by three sub-criticalphotoperiodic cycles if ABA was applied to apices released fromapical dominance. In this case formation of lateral organs andinternodes was promoted by ABA and was followed by stimulatedinflorescence formation. Gibberellic acid (GA2) at 1x 10^–4M or 3 x 10^–4 M brought about a similar effect on floweringas ABA, although the primary growth effect was different, i.e.GA₂ stimulated longitudinal growth. The effects of ABA and GA₂ on floral differentiation have beencompared with earlier results obtained from auxin and kinetinapplications. These growth hormones are believed to regulateflowering by changing cellular growth within the shoot apex.Depending on the actual state of the meristem identical growthresponses may result in different patterns of organogenesisand even in opposite effects on flowering. Shoot apex, flowering, photoperiodic induction, abscisic acid, gibberellic acid, Chenopodium rubrum L.     

Involvement of cellulose synthesis in actions of gibberellin and kinetin on cell expansion. Gibberellin-coumarin and kinetin-coumarin interactions on stem elongation

In azuki bean (Azukia angularis = Vignia angularis) epicotylsections, 5 ? 10^–4 M coumarin inhibited the incorporationof radioactivity from [U^–14C]glucose into the cellulosefraction by 35% in the absence of indole-3-acetic acid (IAA)and by 40% in the presence of 1 ? 10^–4 M IAA. There wasno inhibitory effect on the incorporation of radioactivity intothe other fractions. Coumarin at 5 ? 10^–4 M reversed thepromoting effect of 1 ? 10^–5 M gibberellin A₃ (GA) andthe inhibitory effect of 1 ? 10^–5 M kinetin on IAA-inducedelongation of sections with no significant effects on IAA-inducedelongation. Neither GA nor kinetin had any appreciable effectson cellulose synthesis. No inhibition of cellulose syntheiswas observed with 1 ? 10^–3 M colchichine, which has beenreported to have effects similar to those of coumarin on GA-or kinetin-affected stem elongation. Coumarin at 5 ? 10^–4M was ineffectual in breaking up wall microtubules, while adisrupting effect on wall microtubules was clearly demonstratedwith 3 ? 10^–4M colchicine. From these results, the possible involvement of cellulose synthesisin cell expansion controlled by GA or kinetin was suggested. (Received August 3, 1973; )     

A study on senescence in tobacco leaf disks II. Chloroplast and cytoplasmic rRNAs

In tobacco leaf disks floated on water in the dark, chloroplastrRNA (23S and 16S rRNA) decreased rapidly, and this decreasewas inhibited by 10^–6M BA. The cytoplasmic rRNA (25S and18S rRNA) level changed little during a few days of dark incubationregardless of the presence or absence of BA. Cycloheximide at10^–5 M completely removed the effect of BA. ChloroplastrRNA and cytoplasmic rRNA respectively decreased and increasedduring a 4-day culture in the light, and BA had no influenceon these light effects. (Received December 2, 1974; )