Changes in respiration of mitochondria isolated from cotyledons of ethylene-treated pea seedlings

Treatment of intact, germinating pea (Pisum sativum L. cv. Homesteader) seedlings with ethylene enhanced the cyanide-resistant respiration of mitochondria isolated from the cotyledons. The level of enhancement depended on the concentration of ethylene. Thus, exposure to 0.9 l·l^-1 of ethylene in air for days 4–6 of germination had little effect on cyanide-resistant respiration, while exposure to 130 l·l^-1 increased it from 10 to 50 nmol O₂·min^-1·(mg protein)^-1. The length of exposure to ethylene also affected the degree of enhancement. According to some literature data, lipoxygenase (EC 1.13.11.12) activity can be mistaken for cyanide-resistant respiration, but in our preparations of purified pea mitochondria ethylene had no effect on lipoxygenase activity, nor did the gas disrupt the outer mitochondrial membrane. Bahr and Bonner plots of respiration in the presence of salicylhydroxamic acid (SHAM) indicated that ethylene did not affect respiration proceeding via the cytochrome pathway. Thus, increases in total respiration in mitochondria from cotyledons of ethylene-treated pea seedlings reflect increases in cyanide-resistant respiration.Abbreviations Cyt c cytochrome c - SHAM salicylhydroxamic acid     

Enhancement of specific nitrogenase activity inAzospirillum brasilense andKlebsiella pneumoniae,inhibition inRhizobium japonicum under air by phenol

Specific nitrogenase activity inAzospirillum brasilense ATCC 29145 in surface cultures under air is enhanced from about 50 nmol C₂H₄·mg protein^-1·h^-1 to 400 nmol C₂H₄ by the addition of 1 mM phenol. 0.5 and 2 mM phenol added increase the rate 5-fold and 4-fold. This enhancement effect is observed only between 2 and 3 days after inoculation, with only a small reduction of the growth of the cells by the phenol added. In surface cultures under 1% O₂, nitrogenase activity is slightly reduced by the addition of 1–0.01 mM phenol. Utilization of succinate is enhanced during the period of maximum enhancement of nitrogenase activity by 60% by addition of 1 mM phenol. The cells did not produce¹⁴CO₂ from [U-¹⁴C] phenol, neither in surface cultures nor in liquid cultures and less than 0.1% of the phenol was incorporated into the cells. A smaller but significant enhancement of nitrogenase activity by about 100% in surface cultures under air was found withKlebsiella pneumoniae K 11 after addition of 1 mM phenol. However, inRhizobium japonicum 61-A-101 all phenol concentrations above 0.01 mM reduced nitrogenase activity. With 1 mM phenol added activity was reduced to less than 10% with no effect on the growth in the same cultivation system. With thisRhizobium japonicum strain significant quantities of phenol (25 mol in 24 h by 2·10¹² cells) were metabolized to¹⁴CO₂, with phenol as sole carbon source. WithAzospirillum brasilense in liquid culture under 1% and 2% O₂ in the gas phase, no enhancement of nitrogenase activity by phenol was noticed.     

N2 fixation by red alder (Alnus rubra) and scotch broom (Cytisus scoparius) planted under precommerically thinned Douglas-fir (Pseudotsuga menziesii)

Summary From acetylene reduction assays over a 10-month period starting in April 1979, nodule activities averaged 18.78 (se 4.67) moles C₂H₄ g nodule dw^–1 h^–1 forAlnus rubra and 59.95 (se 12.14) moles C₂H₄ g nodule dw^–1 h^–1 forCytisus scorparius. Plant rates were 1.91 (se. 47) moles C₂H₄ plant^–1 h^–1 forA. rubra and 0.55 (se. 17) moles C₂H₄ plant^–1 h^–1 forC. Scoparius. Plant activity and total leaf N were strongly correlated with the dw of other plant parts, but nodule activity and percent leaf N were not. Plant and nodule activities were not associated with temperature, moisture stress, precipitation events or percent light for either species over the growing season nor for 54A. rubra sampled in mid-season 1979 on one replication. After 5 to 6 growing seasons, 14A. rubra on the same site ranged from 30 to 332 cm in height and showed strong correlation between nodule dw, leaf dw, plant size and total leaf N. Results from this study and others indicate logistic equations may be modified to predict the effect of adding a N₂ fixing plant to a population of non N₂ fixing trees.     

Auxin-induced Ethylene Production and Its Inhibition by Aminoethyoxyvinylglycine and Cobalt Ion

Auxin is known to stimulate greatly both C₂H₄ production and the conversion of methionine to ethylene in vegetative tissues, while amino-ethoxyvinylglycine (AVG) or Co²⁺ ion effectively block these processes. To identify the step in the ethylene biosynthetic pathway at which indoleacetic acid (IAA) and AVG exert their effects, [3-¹⁴C]methionine was administered to IAA or IAA-plus-AVG-treated mung bean hypocotyls, and the conversion of methionine to S-adenosylmethionine (SAM), 1-amino-cyclopropane-1-carboxylic acid (ACC), and C₂H₄ was studied. The conversion of methionine to SAM was unaffected by treatment with IAA or IAA plus AVG, but active conversion of methionine to ACC was found only in tissues which were treated with IAA and which were actively producing ethylene. AVG treatment abolished both the conversion of methionine to ACC and ethylene production. These results suggest that in the ethylene biosynthetic pathway (methionine → SAM → ACC → C₂H₄) IAA stimulates C₂H₄ production by inducing the synthesis or activation of ACC synthase, which catalyzes the conversion of SAM to ACC. Indeed, ACC synthase activity was detected only in IAA-treated tissues and its activity was completely inhibited by AVG. This conclusion was supported by the observation that endogenous ACC accumulated after IAA treatment, and that this accumulation was completely eliminated by AVG treatment. The characteristics of Co²⁺ inhibition of IAA-dependent and ACC-dependent ethylene production were similar. The data indicate that Co²⁺ exerts its effect by inhibiting the conversion of ACC to ethylene. This conclusion was further supported by the observation that when Co²⁺ was administered to IAA-treated tissues, endogenous ACC accumulated while ethylene production declined.     

Role of ethylene in postharvest quality of cut oriental lily ‘Stargazer’

The effects of endogenous and exogenous C₂H₄ and C₂H₄ inhibitors on the postharvest leaf and flower quality of Oriental lily Stargazer were investigated. Endogenous C₂H₄ was not produced by freshly harvested excised leaves or flowers. Treatment of freshly harvested excised flowers, buds, leaves, and intact cut stems with C₂H₄ concentrations as high as 10 µl·l^–1 did not affect bud opening or longevity or the development of leaf yellowing. Therefore, treatment with anti-C₂H₄ compounds, such as silver thiosulfate (STS) and 1-methylcyclopropene (1-MCP), did not improve the quality of the flowers. Data thus indicate that freshly harvested Stargazer were not sensitive to C₂H₄. Sensitivity of Stargazer to C₂H₄, however, increased dramatically following cold storage, as exposure of cold-stored stems to C₂H₄ concentrations as low as 0.3 µl·l^–1 significantly affected bud opening. The development of leaf yellowing on cold-stored stems was not affected by the exogenous C₂H₄. Pretreating cold-stored stems with 1-MCP significantly reduced blasting of small buds that failed to develop due to carbohydrate depletion and reduced the percentage of buds that did not fully open. Concurrently, 1-MCP did not affect the quality of the leaves. These data indicate that sensitivity of cut lilies to C₂H₄ differs following cold storage and that 1-MCP is a more suitable anti-C₂H₄ compound than STS. Furthermore, studies on endogenous C₂H₄ production revealed that, while C₂H₄ was not detected in freshly harvested buds and leaves, it was produced by both following cold storage. The latter produced C₂H₄ at a higher rate than the former. Results of this study clearly indicate that there are two situations in which lilies will benefit from pretreatment with an anti-C₂H₄ compound (1) when cut stems contain buds that are marginally small for opening and (2) when cut stems will be cold stored before marketing.     

Molecular weight and quaternary structure of ribulose bisphosphate carboxylase from the cyanobacterium,Synechococcus sp.

Inhibition of photosynthetic growth of Rhodopseudomonas capsulata by metronidazole was dependent on the nitrogen supply in culture solutions. Cultures fixing dinitrogen were more susceptible to inhibition by low concentrations than those supplied with NH ₄ ⁺ . Light-dependent C₂H₂ reduction and H₂ production by washed cells were inhibited by 80% and 60% respectively by 1 mM metronidazole. When this compound was first reduced with H₂-palladised asbestos prior to assay, it only partially restricted C₂H₂ reduction in washed cells (33%) compared with unreduced inhibitor (68%). Metronidazole was without effect on other metabolic functions. Thus, even at 40 mM it did not inhibit either (a) dark or light respiration in cells grown under photo- and chemo-heterotrophic conditions; (b) H₂-dependent photoreduction of ¹⁴CO₂; (c) -glutamyltransferase activity of glutamine synthetase in cell-free extracts (25 mM inhibitor).Metronidazole (1 mM) completely inhibited C₂H₂ reduction by washed cells of Azotobacter vinelandii. The dithionite-dependent C₂H₂ reduction of a partially purified nitrogenase was only partially inhibited (30%) by 1 mM metronidazole.     

Regulation of growth in stem sections of deep-water rice

Submergence in water greatly stimulates internodal elongation in excised stem sections of deep-water rice (Oryza sativa L. cv. Habiganj Aman II) and inhibits growth of leaf blades and leaf sheaths. The highest rates of internodal growth have been observed in continuous light. Very little growth occurs in submerged sections kept in darkness or incubated under N₂ in the light. The effect of submergence on the growth of deep-water rice is, at least in part, mediated by C₂H₄, which accumulates in the air spaces of submerged sections. This accumulation results from increased C₂H₄ synthesis in the internodes of submerged sections and reduced diffusion of C₂H₄ from the tissue into the water. Increased C₂H₄ levels accelerate internodal elongation and inhibit the growth of leaves. Compounds capable of changing the rate of C₂H₄ synthesis, namely aminoethoxyvinylglycine, an inhibitor of C₂H₄ synthesis, and 1-aminocyclopropane-1-carboxylic acid, the immediate, precursor of C₂H₄, have opposite effects on growth of internodes and leaves. The enhancement of internodal elongation by C₂H₄ is particularly pronounced in an atmosphere of high CO₂ and low O₂. The increase in C₂H₄ synthesis in internodes of submerged sections is primarily triggered by reduced atmospheric concentrations of O₂. The rate of C₂H₄ evolution by internodes isolated from stem sections and incubated in an atmosphere of low O₂ is up to four times greater than that of isolated internodes incubated in air. In contrast, C₂H₄ evolution from the leaves is reduced under hypoxic conditions. The effect of submergence on growth of stem sections of deep-water rice can be mimicked by exposing non-submerged sections to a gas mixture which is similar to the gaseous atmosphere in the internodal lacunae of submerged sections, namely 3% O₂, 6% CO₂, 91% N₂ (by vol.) and 1 l l^-1 C₂H₄. Our results indicate that growth responses obtained with isolated rice stem sections are similar to those of intact deep-water rice plants.Abbreviations ACC 1-aminocyclopropane-1-carboxylic acid - AVG aminoethoxyvinylglycine     

Effect of ethylene and 1-methylcyclopropene on chlorophyll catabolism of broccoli florets

Branchlets of broccoli (Brassica oleracea L.) were used to examine ethylene-stimulated chlorophyll catabolism. Branchlets treated with: 1) air (CK); 2) 1 µL·L^–1 1-methylcyclopropene (1-MCP) for 14 hr at 20 °C; 3) 1000 µL·L^–1 ethylene (C₂H₄) for 5 hr at 20 °C; or 4) 1-MCP then C₂H₄, were stored in the dark at 20 °C for up to 3 d. Chlorophyll (Chl) content and branchlet hue angle decreased during the storage period and 1-MCP treatment delayed this change. Chl degradation in broccoli was accelerated by exposure to C₂H₄, especially for Chl a. Prior treatment with 1-MCP prevented degreening stimulated by C₂H₄. Lipoxygenase activity was not altered by any of the treatments, however, 1-MCP with or without ethylene resulted in reduced activity of chlorophyllase (Chlase) and peroxidase (POD). Exposure to C₂H₄ stimulated Chlase activity and extended the duration of high POD activity. Treatment with 1-MCP followed by C₂H₄ resulted in reduced POD activity and delayed the increase in Chlase activity. The results suggest chlorophyll in broccoli can be degraded via the POD – hydrogen peroxide system. Exposure to C₂H₄ enhances activity of Chlase and extends the duration of high POD activity, and these responses may accelerate degreening. Treatment with 1-MCP delays yellowing of broccoli, an effect that may be due to the 1-MCP-induced reduction in POD and Chlase activities.     

Uptake of [2-14C]abscisic acid and distribution of 14C in apple embryos

Pyrus malus L. var. Golden delicious embryos were incubated with (±)-[2-¹⁴C]abscisic acid (ABA) (10^-5 M, 355 kBq mol^-1). After incubations of various durations, the radioactivity was measured in whole embryos, cotyledons, and embryonic axes.With either 48-h or 16-d incubation periods, the uptake of [¹⁴C]ABA depended upon the mode of culture used. The lowest values corresponded to the absorption by the embryonic axis, the highest to the absorption by the distal parts of the two cotyledons. The cotyledons accumulated the main part of the radioactivity under all conditions. Dormant and almost completely after-ripened embryos cultivated for 4 d showed no significant differences in the radioactivity uptake for identical modes of culture. There was a linear relationship between exogenous ABA concentrations (0.5 to 3.10^-5 M) and ABA uptake for embryos cultivated for 4 d with the distal parts of the cotyledons immersed in the medium.Abbreviations ABA abscisic acid. RM, RM⁺, C/2 M, and CM are different modes of embryo cultures: embryonic axis immersed alone (RM), together with the proximal parts of the cotyledons (RM⁺); distal parts of the cotyledons immersed alone (CM); embroyo flat on the medium, the root and the external surface of one cotyledon being in contact with the medium (C/2 M) - PP proximal parts of the cotyledons - DP distal parts of the cotyledons     

Isolation and characterization of a toxic intracellular protein from Vibrio parahaemolyticus

A toxic factor released from disrupted cells of Vibrio parahaemolyticus was partially purified by gel filtration after precipitation with (NH₄)₂SO₄ at 40% saturation. The factor, which was a thermostable protein of 63 kDa, lysed human erythrocytes at a concentration of 0.15 g ml^-1. Its LD₅₀ by intravenous injection into mice was 6.4 g. Fluid accumulated in suckling mice force-fed with the toxic material (1 to 25 g). Haemolytic activity, which occurred maximall at 37°C and pH 7.0 was enhanced by Ca²⁺, Cu²⁺ and Zn²⁺, each at 1 mm. Anti-toxic-factor serum agglutinated V. parahaemolyticus cells. The factor may play a role in the pathogenesis of V. parahaemolyticus infections and in the host's defence mechanisms against infection by the microorganism.     

Oxidation of ethylene by cotyledon extracts from Vicia faba L.

Improved rates of ethylene oxidation by cell-free preparations from cotyledons of Vicia faba L. have been obtained using cryogenic storage techniques and by developing a method for the hydrolysis of ethylene oxide. Gel permeation chromatography showed that a low-molecular-size fraction was required for activity; accordingly, the kinetics of ethylene oxidation in the presence of this fraction were studied. Reduced pyridine nucleotides could substitute for the low-molecular-size fraction. Activity under a nitrogen atmosphere was 60% lower than in air. The need for reduced nicotinamide adenine dinucleotide phosphate (NADPH) and oxygen indicated that the enzyme might be a mixed-function oxidase. Using sufficient NADPH to approach saturation, the apparent Michaelis constant (K _m) for ethylene was 1.94±0.38 · 10^-8 M (aqueous phase), and when ethylene was saturating, the K _m for NADPH was 3.7 · 10^-5 M. Carbon monoxide was found to inhibit by competing with ethylene, and the inhibitor constant was 5.97 · 10^-7 M in solution. In the presence of excess ethylene and NADPH, activity was highest in phosphate-buffered medium pH 7.9. The bulk of the activity was found in a microsomal fraction.Abbreviations Epps N-2-hydroxyethylpiperazine-N-3-propane sulphinic acid - Tris 2-amino-2-(hydroxymethyl)-1,3-porpanediol     

Rhodium and iridium olefin complexes with bulky cyclopentadienyl and hydrotris(pyrazolyl)borate ligands

The synthesis of a series of rhodium and iridium complexes bearing bulky cyclopentadienyl or hydro(trispyrazolyl)borate ligands is described. The rhodium cyclopentadienyl and hydrotris(pyrazolyl)borate diene compounds, [(η⁵-C₅Me₄Bu^t)Rh(η⁴-2,3-MeRC₄H₄] (R = H, 1; Me, 2) and Tp^MsRh(η⁴-2,3-MeRC₄H₄) (R = H, 3; Me, 4; Tp^Ms is hydrotris(3-mesitylpyrazol-1-yl)borate), respectively, have been prepared from the corresponding Rh(I) diene precursors and Zn(C₅Me₄Bu^t)₂ (for 1 and 2), or TlTp^Ms (for 3 and 4), as effective C₅Me₄Bu^t or Tp^Ms transfer reagents. In contrast with these results, attempts to obtain a bis(ethylene) derivative of the Tp^tolIr(I) unit (Tp^tol stands for hydrotris(3-p-tolylpyrazol-1-yl)borate) have provided instead the Ir(III) complex [(κ⁴-N,N′,N″,C-Tp^tol)-Ir(C₂H₅)(C₂H₄)] (5), whose formation requires C-H bond activation of a molecule of ethylene and of one of the Tp^tolp-tolyl substituents. In refluxing toluene 5 experiences metalation of a second p-tolyl substituent to give [(κ⁵-N,N′,N″,C,C′-Tp^tol)-Ir(C₂H₄)] (6), which features unusual κ⁵-Tp^tol coordination. The latter compound reacts with carbon monoxide to yield the corresponding carbonyl, 7.     

Freezing injury in cold-acclimated and unhardened spinach leaves

Spinach plants (Spinacia oleracea L.) were frost-hardened by cold-acclimation to 1° C or kept in an unhardy state at 20°/14° C in phytotrons. Detached leaves were exposed to temperatures below 0°C. Rates of photosynthetic CO₂ uptake by the leaves, recorded after frost treatment, served as a measure of freezing injury. Thylakoid membranes were isolated from frost-injured leaves and their photosynthetic activities tested. Ice formation occurred at about-4° to-5° C, both in unhardened and cold-acclimated leaves. After thawing, unhardened leaves appeared severely damaged when they had been exposed to-5° to-8° C. Acclimated leaves were damaged by freezing at temperatures between-10° to-14° C. The pattern of freezing damage was complex and appeared to be identical in hardened and unhardened leaves: 1. Inactivation of photosynthesis and respiration of the leaves occurred almost simultaneously. 2. When the leaves were partly damaged, the rates of photosynthetic electron transport and noncyclic photophosphorylation and the extent of light-induced H⁺ uptake by the isolated thylakoids were lowered at about the same degree. The dark decay of the proton gradient was, however, not stimulated, indicating that the permeability of the membrane to-ward protons and metal cations had not increased. 3. As shown by partial reactions of the electron transport system, freezing of leaves predominantly inhibited the oxygen evolution, but photosystem II and photosystem I-dependent electron transport were also impaired. 4. Damage of the chloroplast envelope was indicated by a decline in the percentage of intact chloroplasts found in preparations from injured leaves. The results are discussed in relation to earlier studies on freezing damage of thylakoid membranes occurring in vitro.Abbreviations Chl chlorophyll - DCPIP 2,6-dichlorophenol indophenol - HEPES N-2-hydroxyethylpiperazine-N-2-ethane sulfonic acid - MES 2(N-morpholino) ethane sulfonic acid     

Ethylene homopolymerization and ethylene/1-hexene copolymerization catalysed by mixed salicylaldiminato cyclopentadienyl zirconium complexes

Three new mixed salicylaldiminato cyclopentadienyl zirconium complexes Cp′[2-Bu^t-6-(C₆H₁₁NCH)C₆H₃O]ZrCl₂ (Cp′ = ⁿBuC₅H₄ (3a), ^tBuC₅H₄ (3b) and Me₄C₅H (3c)) were prepared and the structure of complex 3c was confirmed by X-ray diffraction analysis. All of the three complexes showed high activities for ethylene homopolymerization with the activation of methylaluminoxane, and 3a showed the highest activity up to 1.15 × 10⁶ g PE/mol Zr h for ethylene homopolymerization at 70 °C. The ¹³C NMR spectrum showed that the obtained polymer is linear polyethylene. Complexes 3a-c also catalysed ethylene/1-hexene copolymerization with high activities from 6.29 × 10⁵ to 12.3 × 10⁵ g Copolymer/mol Zr h and with 0.89-1.39% 1-hexene incorporation level. In addition, the influence of the substituted alkyl on Cp on the catalytic behavior of corresponding zirconium complexes was discussed.     

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.     

Nitrogen fixation in subarctic streams influenced by beaver (Castor canadensis)

Nitrogen fixation was measured in four subarctic streams substantially modified by beaver (Castor canadensis) in Quebec. Acetylene-ethylene (C₂H₂ C₂H₄) reduction techniques were used during the 1982 ice-free period (May–October) to estimate nitrogen fixation by microorganisms colonizing wood and sediment. Mean seasonal fixation rates were low and patchy, ranging from zero to 2.3 × 10^–3 µmol C₂H₄ · cm^–2 · h^–1 for wood, and from zero to 7.0 × 10^–3 µmol C₂H₄ · g AFDM^–1 · h^–1 for sediment; 77% of all wood and 63% of all sediment measurements showed no C₂H₂ reduction. Nonparametric statistical tests were unable to show a significant difference (p > 0.05) in C₂H₂ reduction rates between or within sites for wood species or by sediment depth.Nitrogen contributed by microorganisms colonizing wood in riffles of beaver influenced watersheds was small (e.g., 0.207 g N · m^–2 · y^–1) but greater than that for wood in beaver ponds (e.g., 0.008 g N · m^–2 · y^–1) or for streams without beaver (e.g., 0.003 g N · m^–2 · y^–1). Although mass specific nitrogen fixation rates did not change significantly as beaver transform riffles into ponds, the nitrogen fixed by organisms colonizing sediment in pond areas (e.g., 5.1 g N · m^–2 · y^–1) was greater than that in riffles (e.g., 0.42 g N · m^–2 · y^–1). The annual nitrogen contribution is proportional to the amount of sediment available for microbial colonization. We estimate that total nitrogen accumulation in sediment, per unit area, is enhanced 9 to 44 fold by beaver damming a section of stream.     

Culture conditions effecting plant regeneration from cotyledons of Vigna radiata (L.) Wilczek

Conditions for plant regeneration from excised cotyledons of Vigna radiata were studied. Complete plant developed from the uncallused proximal ends of cotyledons on Murashige & Skoog's (MS), Gamborg's (B₅) and C (MS salts + B₅ vitamins) basal media. The basal medium C was found to be best for plant regeneration. Regeneration frequency, however, varied with genotype, size, orientation and age of explant and the different plant growth regulators combination in the medium. Addition of cytokinins induced callusing at the proximal ends of cotyledons followed by multiple shoot formation. Out of 6-benzyl aminopurine (BAP), kinetin (KIN), N (^–2 isopentyl) adenine (2iP) and adenine sulphate (AS), only BAP and KIN were found to be more effective in enhancing the frequency of shoot regeneration. BAP at 1×10^-1M induced maximum (60%) shoot regeneration whereas maximum number of shoots (8 to 9 shoots) per explant was observed with 5×10^-6M BAP. Cotyledons excised from two-day old seedlings were most regenerative. The regenerative response of cotyledons decreased when sliced into two equal parts either longitudinally or transversely. Callusing and organogenic differentiation occured only if the petiolar end of cotyledons was in contact with medium. None of the tested treatments were effective in inducing shoot bud differentiation from subcultured callus. Well developed shoots rooted when incubated on half strength MS, MS and MS basal medium supplemented with IAA (5×10^-6M). The rooted plants were transferred to pots and later established in the field with 60% success.Abbreviations AS adenine sulphate - BAP 6-benzylaminopurine - B₅ medium after Gamborg et al. [6], - C Medium with MS salts + B₅ vitamins - 2iP N (^–2 isopentyl) adenine - IAA indole-3-acetic acid - KIN Kinetin - MS medium after Murashige & Skoog [21] - NAA 1-napthaleneacetic acid     

Reactivity of a new family of diamido-diamine cyclam-based zirconium complexes in ethylene polymerization

Compounds of general formula [(^∗Bn₂Cyclam)ZrCl₂] (^∗Bn = 4-^tBuC₆H₄CH₂, (4) and 4-CF₃C₆H₄CH₂, (5)) were synthesised using Zr(CH₂SiMe₃)₂Cl₂(Et₂O)₂ and the corresponding ligand precursors 1,8-(4-^tbutylbenzyl)-1,4,8,11-tetraazacyclotetradecane (H₂(4-^tBuBn)₂Cyclam), (4a), and 1,8-(4-trifluoromethylbenzyl)-1,4,8,11-tetraazacyclotetradecane (H₂(4-CF₃Bn)₂Cyclam), (5a). Complexes 4 and 5, in addition to other [(^∗Bn₂Cyclam)ZrCl₂] compounds previously described by some of us (^∗Bn = PhCH₂, (1), 3,5-Me₂C₆H₃CH₂, (2) and 3,5-^tBu₂C₆H₃CH₂, (3)) were tested in the polymerization of ethylene in the presence of MAO. System 4/MAO presents the highest activity (2790 g PE molZr⁻¹ h⁻¹ atm⁻¹). The polymers formed are slight to moderately branched polyethylenes with a percentage of branching ranging between 1.2% and 3.3%. The melting points obtained by differential scanning calorimetry (DSC) ranging from 128 to 140 °C, are consistent with rather high average molecular weight polymers with crystallinity close to 50%.     

Nitrogen fixation byRubus ellipticus J. E. Smith

Summary Nitrogenase activity as assayed by acetylene reduction was observed in detachedRubus ellipticus J. E. Smith root nodules collected in the field and tested under ambient conditions. The nitrogenase activity was 8.4 moles C₂H₄.gfr. wt nodule^–1.h^–1 or 24.0 moles C₂H₄.g dry wt nodule^–1.h^–1 being at a rate comparable with that measured in some other non-legumes assayed in Java at the same time under similar conditions. Nodule morphology bore little resemblance to the root nodules of other non-leguminous plants and nodule structure was different from the other rosaceous examples.The endophyte inhabiting the root nodules was actinomycetal.