Transport and Metabolism of 1-Aminocyclopropane-1-carboxylic Acid in Sunflower (Helianthus annuus L.) Seedlings

Transport and metabolism of [2,3-¹⁴C] 1-aminocyclopropane-1-carboxylic acid (ACC) from roots to shoots in 4-day-old sunflower (Helianthus annuus L.) seedlings were studied. [¹⁴C]ACC was detected in, and ¹⁴C₂H₄ was evolved from, shoots 0.5 hours after [¹⁴C]ACC was supplied to roots. Ethylene emanation from the shoots returned to normal levels after 6 hours. The roots showed a similar pattern, although at 24 hours ethylene emanation was still slightly higher than in those plants that did not receive ACC. [¹⁴C]N-malonyl-ACC (MACC) was detected in both tissues at all times sampled. [¹⁴C]MACC levels surpassed [¹⁴C]ACC levels in the shoot at 2 hours, whereas [¹⁴C]MACC levels in the root remained below [¹⁴C]ACC levels until 6 hours, after which they were higher. Thin-layer chromatography analysis identified [¹⁴C] ACC in 1-hour shoot extracts, and [¹⁴C]MACC was identified in root tissues at 1 and 12 hours after treatment. [¹⁴C]ACC and [¹⁴C] MACC in the xylem sap of treated seedlings were identified by thin-layer chromatography. Xylem transport of [¹⁴C]ACC in treated seedlings, and transport of ACC in untreated seedlings, was confirmed by gas chromatography-mass spectrometry. Some evidence for the presence of [¹⁴C]MACC in xylem sap in [¹⁴C]ACC-treated seedlings is presented. A substantial amount of radioactivity in both ACC and MACC fractions was detected leaking from the roots over 24 hours. A second radiolabeled volatile compound was trapped in a CO₂-trapping solution but not in mercuric perchlorate. Levels of this compound were highest after the peak of ACC levels and before peak MACC levels in both tissues, suggesting that an alternate pathway of ACC metabolism was operating in this system.     

Method for Simultaneous Measurement of Radioactive and Inactive CO(2) Evolved from Soil Samples During Incubation with Labeled Substrates

An apparatus is described which allows the simultaneous, continuous, and highly sensitive analysis of inactive and radioactive CO₂ evolved from ¹⁴C-supplemented soils or other materials. The apparatus consists of a control unit, a commercially available conductometric CO₂ analyzer, and fraction collector. A number of model experiments were conducted to demonstrate the potentials of the apparatus. These included analysis of the time course of priming action, when ¹⁴C-glucose was added to soil, separation of CO₂ respiration peaks caused by simultaneous degradation of radioactive and inactive soil supplements, and study of the effects of a fungicide, Benomyl, on degradation of ¹⁴C-labeled glucose. In the last experiment, partial degradation of the fungicide could also be followed.     

C(2)H(4): Its Incorporation and Metabolism by Pea Seedlings under Aseptic Conditions

The effects of various treatments on the recently reported system in pea (Pisum sativum cv. Alaska), which results in (a) the incorporation of ¹⁴C₂H₄ into the tissue and (b) the conversion of ¹⁴C₂H₄ to ¹⁴CO₂, was investigated using 2-day-old etiolated seedlings which exhibit a maximum response. Heat treatment (80 C, 1 min) completely inhibited both a and b, whereas homogenization completely inhibited b but only partially inhibited a. Detaching the cotyledons from the root-shoot axis immediately before exposing the detached cotyledons together with the root-shoot axis to ¹⁴C₂H₄ markedly reduced both a and b. Increasing the ¹⁴C₂H₄ concentration from 0.14 to over 100 μl/l progressively increased the rate of a and b with tissue incorporation being greater than ¹⁴C₂H₄ to ¹⁴CO₂ conversion only below 0.3 μl/l ¹⁴C₂H₄. Reduction of the O₂ concentration reduced both a and b, with over 99% inhibition occurring under anaerobic conditions. The addition of CO₂ (5%) severely inhibited ¹⁴C₂H₄ to ¹⁴CO₂ conversion without significantly affecting tissue incorporation. Exposure of etiolated seedlings to fluorescent light during ¹⁴C₂H₄ treatment was without effect. Similarly, indoleacetic acid, gibberellic acid, benzyladenine, abscisic acid, and dibutyryl cyclic adenosine monophosphate had no significant effect on either a or b.     

Assembly of two low-dimensional coordination polymers from Ag(I) and Cd(II) and 2,3-bis(2-pyridyl)pyrazine

Polydentate nitrogen heterocycle ligand 2,3-bis(2-pyridyl)pyrazine (2,3-dpp) reacted with M(NO₃)_x (M = Ag, x = 1; M = Cd, x = 2) to give two new complexes [Ag(2,3-dpp)(NO₃)]₂ (1) and [Cd(2,3-dpp)(NO₃)₂]_n (2). Both complexes have been characterized by single-crystal X-ray diffraction, elemental analyses, IR and ¹H NMR spectroscopy. Single-crystal X-ray analyses showed that complex 1 crystallized in monoclinic, space group P2₁/n is a dimmer containing penta-coordinated Ag⁺ ion. While compound 2 has 1D chain-like structure with repeat unit Cd(2,3-dpp)(NO₃)₂, in which the Cd(II) presents octa-coordinated N4O4 donor set with two four-membered chelating rings and two five-membered chelating rings around Cd(II) ion. Meanwhile, every neutral chain [Cd(2,3-dpp)(NO₃)₂]_n is mutually connected by face-to-face π?π packing interactions to form a two dimensional layer. Furthermore, antibacterial activities of compound 1 and luminescent property of the compound 2 are also investigated.     

The Metabolism of the Germinating Oil Palm (Elaeis guineensis) Seedling : In Vivo Studies

The metabolism of ¹⁴C-labeled fatty acids and triacylglycerols was followed in intact germinating oil palm seedlings as well as in tissue slices. In the germinating seedling, the shoot contained a normal pattern of membrane fatty acids (mainly C₁₆, C_18:1, C_18:2) but the kernel contained about 68% C₁₂ and C₁₄ fatty acids. Haustorium fatty acids were intermediate between the two. [¹⁴C]Acetate was actively metabolized by shoot and haustorium slices but not so actively by the kernel. Approximately 9% to 17% was converted to water-soluble substances, 4% to 6% to CO₂, and 0.5% to 5.9% to lipids. The fatty acids synthesized in the shoot and haustorium were mainly C₁₆, C₁₈, and C_18:1 fatty acids but in the kernel about 18% to 32% of the ¹⁴C-fatty acids were C₁₂ fatty acids.

[¹⁴C]Lauric acid was absorbed and metabolized by haustorium slices and by the haustorium in intact seedlings; it was partly esterified to triacylglycerols and also converted to water-soluble substances and insoluble tissue material. In contrast, tri-[¹⁴C]laurin was absorbed but not metabolized. The haustorium also absorbed other fatty acids but the longer chain (C₁₆ and C₁₈) fatty acids were not esterified or metabolized further. Preincubation of the haustorium with plant hormones or in the presence of kernel tissue did not alter its inactivity towards tri-[¹⁴C]laurin.

When tri-[¹⁴C]laurin or [¹⁴C]lauric acid were injected into the seed or the shoot, there was no movement or radioactivity to other parts of the seedling. When injected into the shoot, but not into the seed, tri-[¹⁴C] laurin was hydrolyzed and partly metabolized to water-soluble substances.

     

Selective Inhibition of the Demethylation at C-14 in Ergosterol Biosynthesis by the Fungicide,Denmert (S-1358)

In cell-free homogenates of Saccharomyces cerevisiae, Denmert (S-1358) inhibited the incorporation of radioactivity from dl-mevalonate-2-¹⁴C into 14-desmethyl-lanosterol, 4α-methyl-cholesta-8,24-dien-3-one, 4α-methyl-zymosterol and 4-desmethyl sterols (zymosterol and episterol) at a concentration of 10^?4 m. Concomitantly, a large accumulation of radioactivity was observed in the Ianosterol fraction.

In good agreement with the results described above, Denmert inhibited the conversion of ¹⁴C-labeled lanosterol to 4-desmethyl sterols, while the conversion of ¹⁴C-labeled 14-desmethyl-lanosterol to 4-desmethyl sterols was hardly affected by the fungicide. It is therefore evident that Denmert is a potent selective inhibitor of the demethylation at the C–14 position in ergosterol biosynthesis.

The fungicide, triarimol, was also found to exhibit the same effect on sterol biosynthesis as Denmert.     

Comparative uptake of nitrate by intact seedlings of C3 (barley) and C4 (corn) plants: Effect of light and exogenously supplied sucrose

The effect of light and exogenously supplied sucrose on NO₃ ⁻ uptake was studied in 9-day-old intact C₃ (barley) and C₄ (corn) seedlings. The seedlings used were uninduced for nitrate uptake system (i.e. had never seen nitrogen during germination and growth) and were exposed to continuous light for 3 days to avoid any diurnal variation and to load the seedlings fully with photosynthates. The uptake assay was conducted either in light or in darkness. Prior to assay, seedlings were treated with darkness or light for 24 h. Accordingly, four sets of seedlings, i.e. pretreated with light and assayed in light (LL); pretreated and assayed in darkness (DD); pretreated with light and assayed in darkness (LD); and pretreated with darkness and assayed in light (DL) were formed. Barley exhibited 55% higher NO₃ ⁻ uptake than corn during light (LL) and 91% higher during darkness (DD). Shifting barley seedlings from light to dark (LD) or dark to light (DL) for uptake assay, did not affect NO₃ ⁻ uptake, i.e. in LD the uptake was similar to LL and in DL it was similar to DD. However, in corn, the light conditions during the assay determined the uptake regardless of the conditions during the period preceding the assay. One percent sucrose in the medium increased NO₃ ⁻ uptake by 31% in barley and 70% in corn during light (LL). The corresponding increase during darkness (DD) was 38% in both barley and corn. Removal of the corn residual endosperm decreased NO₃ ⁻ uptake by 40% during darkness. Etiolated seedlings (those having never seen light) of both barley and corn were able to take up significant amount of NO₃ ⁻ during darkness. Externally supplied sucrose in the assay medium of etiolated seedlings increased the NO₃ ⁻ uptake to about 4 and 2 fold in barley and corn, respectively. The data presented here provide evidence that: 1. In intact seedlings, light per se is not obligatory for NO₃ ⁻ uptake and that the carbohydrate supply may mimic light. 2. Light affected the NO₃ ⁻ uptake differently in barley and corn. This revised version was published online in June 2006 with corrections to the Cover Date.     

Metabolism of tritiated gibberellin a(20) in maize

After the application of 2.36 Curies per millimole [2,3-³H]gibberellin A₂₀ (GA₂₀) to 21-day-old maize (Zea mays L., hybrid CM7 × CM49) plants, etiolated maize seedlings, or maturing maize cobs, a number of ³H-metabolites were observed. The principal acidic (pH 3.0), ethyl acetate-soluble metabolite was identified as [³H]GA₁ on the basis of co-chromatography with standard [³H]GA₁ on SiO₂ partition, high resolution isocratic elution reverse phase C₁₈ high performance liquid chromatography and gas-liquid chromatography radiocounting. Two other acidic metabolites were identified similarly as [³H]GA₈ and C/D ring-rearranged [³H]GA₂₀, although gas-liquid chromatography radiocounting was not performed on these metabolites. Numerous acidic, butanol-soluble (e.g. ethyl acetate-insoluble) metabolites were observed with retention times on C₁₈ high performance liquid chromatography radiocounting similar to those of authentic glucosyl conjugates of GA₁ and GA₈, or with retention times where conjugates of GA₂₀ would be expected to elute. Conversion to [³H]GA₁ was greatest (23% of methanol extractable radioactivity) in 21-day-old maize plants. In etiolated maize seedlings, the C/D ring-rearranged [³H]GA₂₀-like metabolite was the major acidic product, while conversion to [³H]GA₁ was low.     

CO(2) Assimilation by Etiolated Hordeum vulgare Seedlings during the Onset of Photosynthesis

The assimilation of CO₂ by etiolated Hordeum vulgare seedlings during an illumination period indicates a conversion of the organisms to autotrophy.

After 1 hour illumination, increases in the photo-assimilation of CO₂ are observed and the distribution of C¹⁴ in the soluble fraction of the plants is predominantly in intermediates of the Calvin cycle.

     

The synthesis and reaction kinetics of some Co(IIl) and Cr(III) chloro complexes of 1,4,8-Triazaoctane (2,3-tri) and the isolation of chiral trans-dichloro [CoCl2(NH3)(2,3-tri)] ClO4

The reaction of 2,3-tri with CrCl₃·6H₂O₁, dehydrated in boiling DMF, results in the formation of mer-CrCl₃(2,3-tri) and anation of hydrolysed solutions of mer-MCl₃(2,3,-tri) (M=Co, Cr) with 6 M HCl containing HClO₄, forms trans-dichloro- mer-[MCl₂(2,3-tri)(OH₂)]ClO₄·H₂O (M=Cr, Co; I, II). trans-Dinitro-mer-[Co(NO₂)₂(NH₃)(2,3-tri)] ClO₄ crystallises from the reaction between mer-Co(NO₂)₃(2,3-tri) and aqueous 7 M ammonia, on addition of NaClO₄·H₂O, and trans-dichloro-mer-[CoCl₂(NH₃)(2,3-tri)]ClO₄ (III) can be isolated by treatment of the dinitro with 12 M HCl. Reaction of mer-CoCl₃(2,3-tri) with C₂O₄₂⁻, followed by addition of aqueous NH₃ and NaClO₄·H₂O results in the isolation of racemic mer-[Co(ox)(NH₃)(2,3-tri)]ClO₄· H₂O. This complex was resolved into its enantiomeric forms and treatment of these with SOCl₂/MeOH/ HClO₄ gave the chiral forms of trans-dichloro-mer- [CoCl₂(NH₃)(2,3-tri)]ClO₄ (R or S at the see-NH center). The rates of loss of the first chloro ligand from these dichloro complexes have been measured spectrophotometrically in 0.1 M HNO₃ over a 15 K temperature range to give the following kinetic parameters; (I) k_H(298)=7.25 × 10⁻⁵ s⁻¹, E_a=78.5 kJ mol⁻¹, δS₂₉₈^#=₋69 J K⁻¹ mol⁻¹; (II) k_H(298)=4.00 × 10⁻³ s⁻¹, E_a=89.9, δS₂₉₈^#= +87.5; (III) k_H(298)=3.09 × 10⁻⁴ s⁻¹, E_a=103, δS₂₉₈^#=+27. Treatment of the dichloro cations with Hg²⁺/HNO₃ results in the generation of mer- M(2,3-tri)(OH₂)₃³⁺ (M=Cr, Co; IV, V) and trans- diaqua-mer-Co(NH₃)(2,3-tri)(OH₂)₂³⁺ (VI). The Co(III) cations isomerise to the fac configuration with (V) K_isom(298) μ=1.0 M)=2.97 × 10⁻⁵ s⁻¹, E_a=115, δS₂₉₈^#=+46. (VI) K_isom(298) (μ=1.0 M)=4.13 × 10⁻⁵ s⁻¹, E_a=113, δS₂₉₈^#=+52.     

Studies on Effects of Certain Quinones: II. Photosynthetic Incorporation of CO(2) by Chlorella

The effects of various quinone herbicides and fungicides on the photosynthetic ¹⁴CO₂ fixation and the incorporation of ¹⁴C among the products of photosynthesis in Chlorella pyrenoidosa was investigated. Addition of 30 μm 2,3-dichloro-1,4-naphthoquinone (dichlone), 2-amino-3-chloro-1,4-naphthoquinone (06K-quinone), or 2,3,5,6-tetrachloro-1,4-benzoquinone (chloranil) inhibited CO₂ fixation, whereas 1,4-benzoquinone had no effect. Treatment with 3 μm or higher concentrations of dichlone, 06K-quinone or 1,4-benzoquinone also produced marked changes in the pattern of ¹⁴C distribution. A noticeable effect was an increase in the proportion of ¹⁴C in sucrose and glycine accompanied by a reduction in ¹⁴C lipids and glutamic acid. These changes appear to occur as a result of shifts in the flow of carbon along various biosynthetic pathways of photosynthetic CO₂ fixation. It is suggested that inactivation of coenzyme A and shortage of reduced triphosphopyridine nucleotide in the quinone-treated cells inhibited the synthesis of lipids and glutamic acid, thereby diverting more carbon into sucrose and glycine.     

Mercury(II) binding to s4U in E. coli tRNA(Val)

The accessibility of the s⁴U base in native tRNA^Val from E.coli was monitored by studying the binding of various mercurials. The relative binding order HgBr₂[unk]HgCl₂CH₃HgOAc[unk]CH₃HgCl[unk]PCMB parallels approximately the steric requirements of linear HgX₂ or RHgX compounds for S_N2 displacement by sulfur, although other factors are operative. Para-chloromercuri-benzoate (PCMB) does not bind the thiolated nucleotide unless the tertiary structure of the tRNA is opened up by removal of Mg²⁺ ions and heating to 40°. Under these conditions, equilibrium dialysis measurements using ¹⁴C-labeled PCMB showed one binding site (n = 0.93) with an association constant, K₁, of 9 × 10⁴M⁻¹.     

The hormonal control of betacyanin synthesis in Amaranthus caudatus

Gibberellic acid (GA₃) inhibits amaranthin synthesis whereas the growth retardant, phosphon D, enhances pigment levels in A. caudatus seedlings exposed to light. No effect was observed on chlorophyll and carotenoid synthesis. Radioactive tyrosine and DOPA were incorporated into amaranthin. The specific activity of amaranthin synthesised in the presence of ¹⁴C-tyrosine or ¹⁴C-DOPA in seedlings treated with GA₃ is higher than water controls. The specific activity of pigment from phosphon D treated tissue is relatively low. GA₃ treated tissue has lower active tyrosine and DOPA pools compared to phosphon treated seedlings. Tyrosine and DOPA-oxidase activity increases in GA₃ treated and H₂O control seedlings exposed to light. Kinetin stimulates the synthesis of amaranthin in dark-grown seedlings and this is not overcome by simultaneous GA₃ application. Dark-grown seedlings treated with different kinetin concentrations and incubated in ¹⁴C-tyrosine synthesise radioactive amaranthin of similar specific activity. Kinetin treatment of dark-grown seedlings brings about an increased tyrosine and DOPA-oxidase activity. The results indicate that GA₃ controls the production and/or availability of tyrosine whereas kinetin can mimic light treatment and controls the utilisation of tyrosine probably by bringing about the synthesis or activation of tyrosine and DOPA-oxidase protein.     

Carbon fluxes in the rhizosphere of sweet chestnut seedlings (Castanea sativa) grown under two atmospheric CO2 concentrations: 14C partitioning after pulse labelling

Partitioning of ¹⁴C was assessed in sweet chestnut seedlings (Castanea sativa Mill.) grown in ambient and elevated atmospheric [CO₂] environments during two vegetative cycles. The seedlings were exposed to ¹⁴CO₂ atmosphere in both high and low [CO₂] environments for a 6-day pulse period under controlled laboratory conditions. Six days after exposure to ¹⁴CO₂, the plants were harvested, their dry mass and the radioactivity were evaluated. ¹⁴C concentration in plant tissues, root-soil system respiratory outputs and soil residues (rhizodeposition) were measured. Root production and rhizodeposition were increased in plants growing in elevated atmospheric [CO₂]. When measuring total respiration, i.e. CO₂ released from the root/soil system, it is difficult to separate CO₂ originating from roots and that coming from the rhizospheric microflora. For this reason a model accounting for kinetics of exudate mineralization was used to estimate respiration of rhizospheric microflora and roots separately. Root activity (respiration and exudation) was increased at the higher atmospheric CO₂ concentration. The proportion attributed to root respiration accounted for 70 to 90% of the total respiration. Microbial respiration was related to the amount of organic carbon available in the rhizosphere and showed a seasonal variation dependent upon the balance of root exudation and respiration. The increased carbon assimilated by plants grown under elevated atmospheric [CO₂] stayed equally distributed between these increased root activities. ei]H Lambers     

Method for Simultaneous Measurement of Radioactive and Inactive CO2 Evolved from Soil Samples During Incubation with Labeled Substrates

An apparatus is described which allows the simultaneous, continuous, and highly sensitive analysis of inactive and radioactive CO₂ evolved from ¹⁴C-supplemented soils or other materials. The apparatus consists of a control unit, a commercially available conductometric CO₂ analyzer, and fraction collector. A number of model experiments were conducted to demonstrate the potentials of the apparatus. These included analysis of the time course of priming action, when ¹⁴C-glucose was added to soil, separation of CO₂ respiration peaks caused by simultaneous degradation of radioactive and inactive soil supplements, and study of the effects of a fungicide, Benomyl, on degradation of ¹⁴C-labeled glucose. In the last experiment, partial degradation of the fungicide could also be followed.     

Novel 1H-pyrrolo[2,3-c]pyridines as acid pump antagonists (APAs)

A series of 1H-pyrrolo[2,3-c]pyridines as acid pump antagonists (APAs) was synthesized and the inhibitory activities against H⁺/K⁺ ATPase isolated from hog gastric mucosa were determined. After elaborating on substituents at N1, C5, and C7 position of 1H-pyrrolo[2,3-c]pyridine scaffold, we have observed that compounds 14f and 14g are potent APAs with H⁺/K⁺ ATPase IC₅₀ = 28 and 29 nM, respectively.     

Structure and reactivity of [Ru(2,3-Medpp)2Cl2]

The structure and reactivity of the complex [Ru(2,3-Medpp)₂Cl₂](PF₆)₂ (2,3-Medpp⁺=2-[2-(1-methylpyridiniumyl)]-3-(2-pyridyl)pyrazine) was investigated by X-ray diffraction (XRD), ¹H NMR, redox, and UV-Vis absorption measurements. X-ray analysis shows that crystals obtained from an acetonitrile-toluene solution contain the trans-Cl₂, trans-pyrazine isomeric form, while ¹H NMR and redox measurements on the main product of the synthetic workup indicate the presence of the trans-Cl₂, cis-pyrazine isomer. In the dark at 70 °C, the complex [Ru(2,3-Medpp)₂Cl₂]²⁺ reacts slowly in acetonitrile isomerizing to the cis-[Ru(2,3-Medpp)₂(CH₃CN)Cl]³⁺ species. Under ambient light in the presence of excess AgNO₃ the cis-[Ru(2,3-Medpp)₂(CH₃CN)₂]⁴⁺ species is obtained.     

Oxidation of (hydroxyethyl)ferrocene by [2-pyridylmethylbis(2-ethylthioethyl)/amine]copper(II)

A kinetic study of the oxidation of (hydroxyethyl)ferrocene (HEF) by [2-pyridylmethylbis(2-ethyl-thioethyl)ainine]copper(II) (Cu(pmas)²⁺) is reported, with the objective of documenting the influence of the two thioether sulfur ligands on the electron transfer rate. Both reactants exhibit a first-order dependence at pH 6, I = 0.1 M(NaNO₃); k(25°C) = 1.3 × 10⁴M⁻¹sec⁻¹, ΔH3 = 10.1 kcal/mole, ΔS3 = −6 eu. The apparent Cu(pmas)^2+/+ self-exchange electron transfer rate constant calculated from this reaction on the basis of relative Marcus theory (4.7 × 10¹M⁻¹ sec⁻¹) agrees well with previous findings on ferrocytochrome c, Fe(CN)₆⁴⁻, and Ru(NH₃)₅py²⁺ oxidations. Spectrophotometric titrations of Cu(pmas)²⁺ and Cu(tmpa)²⁺ (tmpa = tris(2-pyridylmethyl)amine) with azide ion showed that both Cu(pmas)N₃)⁺ (K_f1 = 3.1 × 10³M⁻¹) and Cu(pmas)(N₃)₂ (K_f2 = 3.5 × 10¹M⁻¹) but Cu(tmpa)(N₃)⁺ (K_f = 6.6 × 10²M⁻¹) are formed up to 0.15 M N₃⁻ (25°C, pH 6, I = 0.2 M), suggesting that a thioether sulfur atom is displaced in the uptake of a second N₃⁻ ion by Cu(pmas)(N₃)⁺. The effect of thioether sulfur displacement by azide ion on the HEF-Cu(pmas)²⁺ reaction rate may be understood entirely through the tendency of N₃⁻ to shift the position of the redox equilibrium towards the reactant side, without invoking any special role for the sulfur ligand in promoting electron transfer reactivity.     

Transport of Benzyladenine and Gibberellin A(1) from Roots in Relation to the Dominance between the Axillary Buds of Pea (Pisum sativum L.) Cotyledons

In etiolated, 5-day-old pea (Pisum sativum L.) seedlings a significantly more intensive growth of buds situated in the axil of the excised cotyledons was observed as early as 4 hours after decapitation and excision of one cotyledon of each pair. If [8-¹⁴C]benzyladenine ([¹⁴C]BA) was applied to roots of intact plants 10 hours prior to such decapitation and excision, significantly higher both total and specific ¹⁴C activities were observed in buds situated on the side of the excised cotyledons as early as 4 hours after decapitation and excision. Although the removal of a substantial part of the root system carried out simultaneously with decapitation and excision of one cotyledon resulted in a decrease in total ¹⁴C activity of buds, nevertheless a higher accumulation of ¹⁴C activity was maintained in buds situated on the side of excised cotyledon. If [¹⁴C]BA was applied to roots of seedlings after they were decapitated and deprived of one cotyledon, both total and specific ¹⁴C activities of buds situated on the side of excised cotyledons were significantly higher as early as the end of uptake of [¹⁴C]BA by roots, i.e. after 10 hours. On the other hand, [1,2-³H]gibberellin A₁ applied to roots of intact and/or decapitated and one-cotyledon-deprived seedlings in the same way as [¹⁴C]BA did not appear in the buds until very much later and only in negligible amounts (i.e.³H activity). This indicates that the release of buds from apical dominance represents an active and selective process which can result from the ability of buds to utilize and/or synthesize only certain growth substances within a certain time interval.     

The Effect of Light on the Tricarboxylic Acid Cycle in Green Leaves: III. A Comparison between Some C(3) and C(4) Plants

The chlorophyll-based specific activity of cytochrome oxidase and three exclusively mitochondrial enzymes of the tricarboxylic acid cycle showed little variation between leaves of C₃ and C₄ plants or between mesophyll and bundle sheath cells of Atriplex spongiosa and Sorghum bicolor. However, a large, light-dependent transfer of label from intermediates of the tricarboxylic acid cycle to photosynthetic products was a feature of leaves of C₄ plants. This light-dependent transfer of label was barely detectable in leaves of C₃ plants and in leaves of F₁ and F₃ hybrids of Atriplex rosea (C₄) and Atriplex patula spp hastata (C₃). The light-dependent transfer of label to photosynthetic products in leaves of C₄ plants was inhibited by the tricarboxylic acid cycle inhibitors malonate and fluoroacetate. The requirement for continued tricarboxylic acid cycle activity was also indicated in experiments with specifically labeled succinate-¹⁴C. These experiments, together with the distribution of ¹⁴C in glucose prepared from sucrose-¹⁴C formed during the metabolism of succinate-2,3-¹⁴C, confirmed that the photosynthetic metabolism of malate and aspartate derived from the tricarboxylic acid cycle, and not the refixation of respiratory CO₂, was the main path of carbon from the cycle to photosynthesis.