Amiprophos-methyl (APM): A rapid,reversible, anti-microtuble agent for plant cell cultures

Summary In plant cell suspension cultures sensitive to the herbicide amiprophos-methyl (APM), 1 to 3 M APM completely depolymerized both cortical and mitotic microtubule (MT) arrays in 1 hour. In comparison, a 2 hour application of 3 mM colchicine had no effect on MT arrays. Recovery from APM treatment occurred as early as 5 minutes after removal of APM. Short, cortical MTs were visible in 3 hours and complete MT arrays were found within 22 hours after drug removal.Sensitivity to APM-induced MT depolymerization varied according to species but was increased or decreased by varying the mitotic rate in cultures. The results indicated APM sensitivity was related to lowered stability of MT arrays in rapidly cycling cells. APM treatment may help distinguish stabilized cortical MTs in elongating cells and nonstabilized cortical MTs in rapidly dividing cells.Abbreviations MT microtubule - APM amiprophos-methyl - DMSO dimethyl sulfoxide - PBS phosphate buffered saline     

The occurrence of HT-2 toxin and other trichothecenes in Norwegian cereals

A total of 449 grain samples, 102 barley, 169 wheat and 178 oat samples were collected from different regions of Norway from 1996–1998 crops, mainly from grain loads and silos. The samples were analysed for type A and B trichothecenes, the largest groups of mycotoxins produced by the Fusarium species, by gas chromatography with mass spectrometric detection (GC-MS). Factors affecting the presence of the different trichothecenes are discussed. Deoxynivalenol (DON) and HT-2 toxin were the trichothecenes most frequently detected, followed by T-2 toxin, nivalenol, and scirpentriol, scirpentriol being detected only in seven samples (>20 g/kg).Oats were the grain species most heavily contaminated with an incidence(% >20 g/kg) and mean concentration of positive samples of 70%(115 g/kg) for HT-2 toxin, 30% (60 g/kg) for T-2 toxin, 57%(104 g/kg) for DON, and 10% (56 g/kg) for nivalenol. The corresponding values for barley were 22% (73 g/kg), 5% (85 g/kg),17% (155 g/kg) and 6% (30 g/kg), and for wheat 1.2% (20 g/kg),0.6% (20 g/kg), 14% (53 g/kg) and 0% for HT-2, T-2, DON and nivalenol, respectively. Norwegian oats were found to contain HT-2 and T-2 toxin in concentrations that might be at threat to human health for high consumers of oats. The amount of DON was significantly lower than in the crop from previous years.This revised version was published online in October 2005 with corrections to the Cover Date.     

Scanning electron microscopy of the rat retina

Summary Fixed and unfixed, freeze-dried pieces of isolated retina and the posterior part of the eye bulb from adult rats were examined in a scanning electron microscope.The inner limiting membrane shows distinct cell borders, protrusions, and scattered microvilli-like structures. Different types of nerve cells are observed in the ganglion cell layer and the inner nuclear layer. They all lack synaptic boutons on the surface of their perikarya. There is an intercellular space between the processes in the nerve fiber layer.The inner and outer segments are surrounded by a space with extracellular material. Their surface is smooth or slightly undulated. There is no evidence indicating the existence of basal infoldings continuous with the membraneous structures inside the rod outer segments. The connecting piece between the inner and outer segments resemble a symmetrically shaped hour-glass. The surface of the epithelial cells is covered by microvilli forming a honeycomb-like structure and each outer segment is surrounded by several microvilli.The results obtained are discussed in relation to those obtained by transmission electron microscopy. The probable existence of a significant extracellular space and the distribution of extracellular material between the segments and the microvilli are discussed.Supported by grants from H. Jeanssons Stiftelse Riksföreningen mot Cancer (265-B69-OIX) and the Swedish Medical Research Council (B70-12X-2534-02). I would like to thank the Swedish Silicate Research Institute, Göteborg, for using their scanning electron microscope, and Miss. M. Persson for skilful technical assistance.     

The supramolecular organization of red algal cell membranes and their participation in the biosynthesis and secretion of extracellular polysaccharides: a review

Summary The relationship between the supramolecular organization of red algal cell membranes and the biosynthesis and secretion of the cell wall skeletal and matrix polysaccharides is reviewed. Freeze-fracture studies have revealed that organized macromolecular structures — linear terminal complexes and tetrads — are present on the plasma membrane and on membranes of the endomembrane system. The linear terminal complexes seem to be involved in the biosynthesis, assembly, and orientation of the cellulose microfibrils and the tetrads in the synthesis of the matrix polysaccharides. It is shown how the research on the supramolecular organization of cell membranes has increased the knowledge on the biosynthesis and secretion of the extracellular crystalline and non-crystalline polysaccharides in red algae. In this review, the progress to date is discussed.Dedicated to Prof. Dr. Dr. h.c. Eberhard Schnepf on the occasion of his retirement     

Immature erythroid cells with novel morphology and cytoskeletal organization in adultXenopus

Summary Nucleated erythrocytes of non-mammalian vertebrates are a useful model system for studying the correlation between changes in cell shape and cytoskeletal organization during cellular morphogenesis. They are believed to transform from spheres to flattened discs to ellipsoids. Our previous work on developing erythroblasts suggested that pointed cells containing incomplete, pointed marginal bands (MBs) of microtubules might be intermediate stages in the larval axolotl. To test whether the occurrence of such pointed cells was characteristic of amphibian erythrogenesis, we have utilized phenylhydrazine (PHZ)-induced anemia in adultXenopus. In this system, circulating erythrocytes are destroyed and replaced by erythroblasts that differentiate in the blood, making them experimentally accessible. Thus, we followed the time-course of morphological and cytoskeletal changes in the new erythroid population during recovery. During days 7–9 post-PHZ, pointed cells did indeed begin to appear, as did spherical and discoidal cells. The percentage of pointed cells peaked at days 11–13 in different animals, subsequently declining as the percentage of elliptical cells increased. Since degenerating old erythrocytes were still present when pointed cells appeared, we tested directly whether pointed ones were old or new cells. Blood was removed via the dorsal tarsus vein, and the erythrocytes washed, fluorescently tagged, and re-injected. In different animals, 2–8% of circulating erythrocytes were labeled. Subsequent to induction of anemia in these frogs, time-course sampling showed that no pointed cells were labeled, identifying them as new cells. Use of propidium iodide revealed large nuclei and cytoplasmic staining indicative of immaturity, and video-enhanced phase contrast and anti-tubulin immunofluorescence showed that the pointed cells contained pointed MBs. The results show that pointed cells, containing incomplete, pointed MBs are a consistent feature of amphibian erythrogenesis. These cells may represent intermediate stages in the formation of elliptical erythrocytes.Abbreviations MB marginal band - MS membrane skeleton - PHZ phenylhydrazine     

Interactions of γ-L-glutamyltaurine with excitatory aminoacidergic neurotransmission

The in vitro effects of -L-glutamyltaurine on different stages of excitatory aminoacidergic neurotransmission were tested with -D-glutamyltaurine as reference. -L-Glutamyltaurine enhanced the K⁺-stimulated release of [³H]glutamate from cerebral cortical slices (25% at 0.1 mM) and slightly inhibited the uptake by crude brain synaptosomal preparations (about 10% at 1 mM). -L-Glutamyltaurine was also a weak displacer of glutamate and its agonists from their binding sites in brain synaptic membrane preparations, being, however, less selective to quisqualate (QA) sites than -D-glutamyltaurine. The basal influx of Ca²⁺ into cultured cerebellar granular cells was not affected by 1 mM -L-glutamyltaurine, but the glutamate- and its agonist-activated influx was significantly inhibited in low-Mg²⁺ (0.1 mM) and Mg²⁺-free media. The glutamate-evoked increase in free intracellular Ca²⁺ and the kainate-activated formation of cGMP in cerebellar slices were both markedly inhibited by 0.1 mM -L-giutamyltaurine. We propose that -L-glutamyltaurine may act as endogenous modulator in excitatory aminoacidergic neurotransmission.     

Segregation analysis in hereditary retinoblastoma

Summary Segregation analysis was performed on 211 nuclear families belonging to 166 pedigrees of hereditary retinoblastoma found in a number of series which have been gathered from the literature. Bilaterally affected carriers appear homogeneous. The segregation ratio in their offspring is 0.49, and the proportion of bilateral cases among affected offspring is 0.87. Both unilaterally affected and unaffected carriers appear heterogeneous. The very low segregation ratio (0.08) in the offspring of unilateral carriers who are not detected through an affected child, suggests the possiblity of two types of carriers, high and low transmitters. The proportions of low transmitters was estimated as 0.14 among all familial unilateral carriers and as 0.45 among all detected unaffected carriers. Unilateral and unaffected high transmitters give a significantly lower segregation ratio than bilaterally affected carriers.On the one hand, the existence of these two different types of carriers provides arguments in support of the hypothesis of delayed mutation. On the other hand, the differences in penetrance among high transmitters, according to their phenotype, supports the hypothesis of host resistance. Under the two-mutation hypothesis, the possibility that the mutation rate is variable among individuals and partly genetically determined, is suggested.     

The evolution of self-fertility inCrepis tectorum (Asteraceae)

The extent of self-fertility was examined in 16 populations ofCrepis tectorum. A hypothesis that a weedy habit favours autogamy was only partly supported. Low levels of self-fertility characterized non-weedy populations from calcareous grasslands (alvars) on the Baltic island in Öland. By contrast, plants in nearly all weed populations studied were more or less self-fertile. However, the trend towards autogamy may have occurred independently of the trend towards a weedy habit, as shown by moderately to high levels of self-fertility in alvar populations from two other Baltic islands. In the weed group, there was a tendency for plants from two field populations to be more autogamous than plants from more ruderal habitats. There was an association between self-fertility and small, inconspicious heads in the alvar group but the association was weaker when weed populations were also considered. The relatively wide heads characterizing the ruderal weed populations may, at least partly, be an indirect effect of increases in overall plant size and/or in the size of the fruit associated with each flower.     

Role of mitogen-activated protein kinase pathway in reactive oxygen species-mediated endothelin-1-induced β-myosin heavy chain gene expression and cardiomyocyte hypertrophy

Endothelin-1 (ET-1) has been found to increase cardiac -myosin heavy chain (-MyHC) gene expression and induce hypertrophy in cardiomyocytes. ET-1 has been demonstrated to increase intracellular reactive oxygen species (ROS) in cardiomyocytes. The exact molecular mechanism by which ROS regulate ET-1-induced -MyHC gene expression and hypertrophy in cardiomyocytes, however, has not yet been fully described. We aim to elucidate the molecular regulatory mechanism of ROS on ET-1-induced -MyHC gene expression and hypertrophic signaling in neonatal rat cardiomyocytes. Following stimulation with ET-1, cultured neonatal rat cardiomyocytes were examined for ³H-leucine incorporation and -MyHC promoter activities. The effects of antioxidant pretreatment on ET-1-induced cardiac hypertrophy and mitogen-activated protein kinase (MAPKs) phosphorylation were studied to elucidate the redox-sensitive pathway in cardiomyocyte hypertrophy and -MyHC gene expression. ET-1 increased ³H-leucine incorporation and -MyHC promoter activities, which were blocked by the specific ET_A receptor antagonist BQ-485. Antioxidants significantly reduced ET-1-induced ³H-leucine incorporation, -MyHC gene promoter activities and MAPK (extracellular signal-regulated kinase, p38, and c-Jun NH₂ -terminal kinase) phosphorylation. Both PD98059 and SB203580 inhibited ET-1-increased ³H-leucine incorporation and -MyHC promoter activities. Co-transfection of the dominant negative mutant of Ras, Raf, and MEK1 decreased the ET-1-induced -MyHC promoter activities, suggesting that the Ras-Raf-MAPK pathway is required for ET-1 action. Truncation analysis of the -MyHC gene promoter showed that the activator protein-2 (AP-2)/specificity protein-1 (SP-1) binding site(s) were(was) important cis-element(s) in ET-1-induced -MyHC gene expression. Moreover, ET-1-induced AP-2 and SP-1 binding activities were also inhibited by antioxidant. These data demonstrate the involvement of ROS in ET-1-induced hypertrophic responses and -MyHC expression. ROS mediate ET-1-induced activation of MAPK pathways, which culminates in hypertrophic responses and -MyHC expression. Tzu-Hurng Cheng, Neng-Lang Shih: These authors have equally contributed to this work     

Tentative immunohistochemical demonstration of melatonin in the rat pineal gland

Summary In the present study an attempt was made to demonstrate melatonin in the rat pineal gland by means of immunohistochemistry. The anti-body used was raised against 5-methoxy-N-acetyltryptophan which is chemically similar to melatonin. Specific fluorescence was demonstrable only in pineals from rats killed during the night, when melatonin formation is high. It was restricted to parenchymal cells lying in a marginal zone of the organ. These results are discussed in relation to a subdivision of the pineal parenchyma into cortical and medullary areas.Supported by a grant of the Deutsche Forschungsgemeinschaft (VO 135/4) within the Schwerpunktprogramm Neuroendokrinologie     

ζ-Potential of n-Alkane Emulsion Droplets and Its Role in Substrate Transport into Yeast Cells

The -potentials of n-alkane droplets, formed by fatty acids, were studied in model systems of the culture liquid of yeasts (Candida maltosa) capable of utilizing n-alkanes. The value of the -potential was found to depend on the droplet size. The negative -potential of submicron droplets was so high that it prevented the droplets from coagulating with cells also possessing a high negative -potential. The dominant role of submicron n-alkane droplets in the kinetics of yeast growth could be accounted for by the existence of a mechanism regulating the contact interactions of individual cells with the droplets followed by the uptake of the substrate.     

Changes in DNA content and chromosomal size during cell culture and plant regeneration of Scilla siberica: selective chromatin diminution in response to environmental conditions

The chromosomal complement and DNA content of cells of the monocotyledonous plant Scilla siberica were studied at various stages of growth, such as callus outgrowths from bulb tissue (bulb callus), callus grown from single protoplasts prepared from bulb callus (protoplast callus), regenerated plants kept for 2–4 years on agar medium and under constant climatic conditions, and regenerated plants grown first for 2 years on agar and then for 1 year in the garden. During callus culture, several different forms of chromatin loss were observed: (1) chromosome elimination early during cell culture, resulting in cells which were mostly diploid but still had large chromosomes similar to those of the original triploid plants (type 1 cells); from these cells no plants could be regenerated. (2) Dramatic reduction in heterochromatin containing the satellite DNA and, apparently subsequently, also of many other chromatin moieties, resulting in the formation of small chromosomes; frequent polyploidization in these cells, resulting in a variable number of chromosomes per cell (preferentially 30–40, in ca. 70% of the cells; type 2 cells). (3) Appearance of a large number of very small (< 1 m) Feulgenpositive chromatin particles (minute chromosomes; often arranged in metaphase-like arrays, suggesting that they were effectively distributed during mitosis). Such cells could survive and divide under cell culture conditions but did not regenerate plants (type 3 cells). In bulb calli, all three cell types were found whereas in protoplast calli only cells of type 2 and 3 were seen. Type 2 and 3 cells had lost, despite their frequent polyploidization, about 80% of their initial nuclear DNA content and an even higher proportion (>95%) of the satellite sequences. Southern DNA blot analysis revealed that sequences hybridizing with certain protein-coding genes such as that for chalcone synthase were also drastically reduced in copy number whereas the proportion of rDNA was even somewhat increased. In plants regenerated from type 2 cells of protoplast calli, which were aneuploid at near-pentaploidy to hexaploidy, further conspicuous changes in chromosomal and DNA content were not observed, as long as they were kept on agar medium and under constant climatic conditions. However, when such plants were grown in the garden for at least 1 year, the satellite DNA as well as the sequences hybridizing with the chalcone synthase gene were disproportionately increased to 30%–40% of their normal proportion, whereas the total DNA had increased by only approximately 15%. The chromosome numbers remained near-pentaploid to hexaploid as in the cell cultures from which these plants had been regenerated. These phenomena of selective loss and regain of chromatin in response to environmental conditions (cell culture, regenerated plants on agar, regenerated plants grown outdoors) are discussed in relation to other forms of chromatin loss, including developmentally controlled chromatin diminution in certain animals.     

Immunocytochemical study of seminal γ-glutamyltransferase using monoclonal antibodies

We produced three monoclonal antibodies, SG1, SG2 and SG3, specific for human seminal -glutamyltransferase when characterized by enzyme-linked immunosorbent assay and immunoblotting. Seminal -glutamyltransferase was localized, by immunostaining, to the epithelial cells of the ductus epididymidis, seminal vesicle and prostate gland with SG1, those of the prostate gland with SG2, and those of the seminal vesicle with SG3. Rabbit polyclonal anti-seminal -glutamyltransferase serum reacted with the proximal convolution of the kidney and the bile capillaries of the liver, and with the epithelial cells of the reproductive organs. However, immunoreactivity was not observed in the kidney or liver with the monoclonal antibodies. Thus, these monoclonal antibodies are probably all specific to seminal -glutamyltransferase but recognize different epitopes.     

Secretion of either of a pair of immunoglobulins,IgM or IgX,in somatic hybrid cells derived by fusion of a B-cell lymphoma cell line carrying both immunoglobulin isotypes

The I.29 cell line is a nonsecreting B-cell leukemia which bears two different immunoglobulin isotypes on its surface, IgM and IgX. The I.29 cells were hybridized with nonsecreting myeloma cells giving rise to dozens of immunoglobulin secreting hybridomas. These fall into three groups differing in the class of immunoglobulin they secrete. Cells of the first group secrete pentameric IgM (, ), those of the second group secrete an unknown immunoglobulin, IgX, which may constitute an allotype of IgA, and those of the third group produce light chains only. The two complete immunoglobulins, IgM and IgX, have the same idiotype, as revealed by serological cross-reactivity of an exhaustively absorbed rabbit anti-idiotype serum.The molecular sizes of the heavy chains of the secreted IgM and IgX are slightly smaller than the and chains, respectively, which are derived from the surface of normal B cells as judged by sodium dodecyl sulfate-polyacrylamide gel electrophoresis.Abbreviations used in this paper Ig immunoglobulin - NMS normal mouse serum - NaDodSO₄ sodium dodecyl sulfate - PAGE polyacrylamide gel electrophoresis - 2ME 2-mercaptoethanol - BPB bromophenol blue - NP40 nonidet P40 This particular immunoglobulin heavy chain has not been fully characterized. It is neither , , nor but is related to, although not identical with, . Because this immunoglobulin has unique properties, it is referred to as IgX.     

Formation of thionates by freshwater and marine strains of sulfate-reducing bacteria

The formation of thionates (thiosulfate, trithionate and tetrahionate) during the reduction of sulfate or sulfite was studied with four marine and four freshwater strains of sulfate-reducing bacteria. Growing cultures of two strains of the freshwater species Desulfovibrio desulfuricans formed up to 400 M thiosulfate and 100 M trithionate under conditions of electron donor limitation. Tetrathionate was observed in lower concentrations of up to 30 M. Uncoupler-treated washed cells of the four freshwater strains formed thiosulfate and trithionate at low electron donor concentrations with sulfite in excess. In contrast, only one of four marine strains formed thionates. The freshwater strain Desulfobulbus propionicus transformed sulfite almost completely to thiosulfate and trithionate. The amounts produced increased with time, concentration of added sulfite and cell density. Tetrathionate was detected only occasionally and in low concentrations, and was probably formed by chemical oxidation of thiosulfate. The results confirm the diversity of the sulfite reduction pathways in sulfate-reducing bacteria, and suggest that thiosulfate and trithionate are normal by-products of sulfate reduction.Abbreviations CCCP carbonyl cyanide m-chlorophenylhydrazone     

Role of the microtubule cytoskeleton in alternating changes in cellulose-microfibril orientation in the coenocytic green alga,Chaetomorpha moniligera

The functions of the microtubule (MT) cytoskeleton in changing the orientation of microfibrils (MFs) in the cell walls of the coenocytic green alga Chaetomorpha moniligera Kjellman were investigated by electron microscopy. The cortical MT cytoskeleton in Chaetomorpha was comprised of longitudinally oriented MTs. Cellulose MFs, however, alternately changed their orientation longitudinally and transversely to form crisscross MF textures. Microtubules were parallel to longitudinally oriented MFs but never to those that were transversely oriented. The average density of MTs during the formation of longitudinally oriented MFs was 216 per 50 m of wall and that of transversely oriented MFs 170/50 m. To determine exactly the MT-density dependency of each MF orientation, changes in MF orientation were examined by changing MT density after treating and removing amiprophos-methyl (APM). Microtubules were reduced in number by a half (100/50 m) after 2 h and by 3/4 (50/50 m) after 3 h of treatment with APM (3 mM). This reduction was caused by the disappearance of alternating MTs. Microtubules retained this density (50/ 50 m) up to 6 h, and then gradually disappeared within 24 h. Microfibril orientation in the innermost cell wall was transverse after treatment with APM for 2 h but was helicoidal after 6 h. Polymerization of MTs occurred in the longitudinal direction following the removal of APM after treatment for 48 h. Microtubule density rose to about 100/50 m and 200/50 m after 6 h and 24 h, respectively. The orientation of MTs changed from helicoidal to transverse and transverse to longitudinal after 6 h and 24 h, respectively. When APM was removed prior to formation of the helicoidal texture, longitudinally oriented MFs appeared within 6 h. There is thus an alternating cycle of formation of longitudinally and transversely oriented MFs within a 12-h period. Formation of transversely oriented MFs as a result of APM treatment started in the middle of a cell as hoops which then extended in the apical and basal directions. Formation of longitudinally oriented MFs as a result of the removal of APM started from the apical end and proceeded toward the base. It follows from these results that: (1) the point of formation of longitudinally oriented MFs differs from that for transversely oriented MFs, (2) MF orientation in each case depends on a separately functioning mechanism, (3) MT density changes rhythmically to trigger a switch for crisscross orientation of MFs.Abbreviations APM amiprophos-methyl - MF microfibril - MT microtubule - TC terminal complex We thank Dr. K. Okuda for making helpful discussion and Miss. T. Matsuki for assistance with replica preparation.     

Presence of plastid and absence of mitochondrial DNA in male reproductive cells as evidence for cytoplasmic inheritance in Turnera ulmifolia and Zantedeschia aethiopica

Summary. Epifluorescence microscopy of mature pollen grains of Turnera ulmifolia and Zantedeschia aethiopica stained with 4,6-diamidino-2-phenylindole demonstrated the presence of fluorescent cytoplasmic DNA aggregates in the male reproductive cells of both species. Double staining of the cells with 4,6-diamidino-2-phenylindole and 3,3-dihexyloxacarbocyanine iodide in Technovit resin sections showed that the mitochondria of these cells did not correspond to the fluorescent cytoplasmic DNA aggregates. Electron microscopy studies revealed both plastids and mitochondria in the cells of these species. In addition, immunoelectron microscopy using an anti-DNA monoclonal antibody showed clear labeling of plastids but not mitochondria. These data provide cytological evidence for biparental plastid inheritance and maternal mitochondrial inheritance in these species.Correspondence and reprints: College of Life Sciences, Peking University, Beijing 100871, Peoples Republic of China.     

Formation of the imidazolides of dinucleotides under potentially prebiotic conditions

Summary Imidazolides of dinucleotides such as ImpApA can be formed from the corresponding dinucleotides in a two-stage process, which gives up to 15% yields under potentially prebiotic conditions. First a solution of the dinucleotide and sodium trimetaphosphate is dried out at constant temperature and humidity. This produces polyphosphates such as pnApA in excellent yield (80%). The products are dissolved in water, imidazole is added, and the solution is dried out again. This yields the 5-phosphorimidazolides.Abbreviations P₃! trimetaphosphate - A adenosine - U uridine - EDTA ethylenediaminetetraacetic acid - Ap adenosine 2(3)-phosphate - Ap! adenosine cyclic 2:3-phosphate - pA adenosine 5-phosphate - pA²p adenosine 2, 5-diphosphate - pA³p adenosine 3, 5-diphosphate - pAp! 5-phospho-adenosine cyclic 2:3-phosphate - ATP adenosine 5-triphosphate - ImpA adenosine 5-phosphorimidazolide - A²pA adenylyl-[25]-adenosine - A³pA adenylyl-[35]-adenosine - A²pU adenylyl-[25]-uridine - A³pU adenylyl-[35]-uridine - pA²pA 5-phosphoadenylyl-[25]-adenosine - pA³pA 5-phospho-adenylyl-[35]-adenosine - pA²pU 5-phospho-adenylyl-[25]-uridine - pA³pU 5-phospho-adenylyl-[35]-uridine - pApN (N= A, U) 5-phosphate of a dinucleoside phosphate - p_nApN (N = A, U; n = 2, 3, 4.) 5-polyphosphate of a dinucleoside phosphate - ImpA²pA imidazolide of pA²pA - ImpA³pA imidazolide of pA³pA - ImpA²pU imidazolide of pA²pU - ImpA³pU imidazolide of pA³pU - ImpApN imidazolide of pApN     

Effect of orchard and postharvest application of daminozide on ethylene synthesis by apple fruit

The effects of daminozide (butanedioic acid-2,2-dimethylhydrazide) on ethylene synthesis by apple fruits were investigated. The objective was to determine the effects of postharvest applications as compared to the standard application of diaminozide in the orchard. Immersion in a solution containing 4.25 g L^–1 active ingredient for 5 min delayed the rise in ethylene production in individual Cox apples at 15°C by about 2 days, whereas orchard application of 0.85 g L^–1 caused delays of about 3 days. Both modes of application depressed the maximal rate of ethylene production attained by ripe apples by about 30%. Daminozide did not affect the stimulation of respiration by ethylene treatment of Gloster apples, but it delayed the increase in ethylene synthesis. Daminozide applied immediately after harvest delayed the rise in ethylene synthesis in Golden Delicious held at 15°C, but it was less effective when applied 48 h after harvest or when apples were held at 5°C. Exposure to 1–2 l L^–1 ethylene for 48 h was less effective in promoting the rise in ethylene in daminozidetreated Cox and Gloster apples than in untreated fruit. High (100–1000 l L^–1) concentrations of ethylene more or less overcame the daminozide effect. Apples absorbed about 40% of surface-applied [¹⁴C]daminozide in 48 h, but more than 90% of the radioactivity in the fruit was recovered from the peel and outer 1 cm of the cortex. Daminozide was partly converted to carbon dioxide and other metabolites.     

The influence of the pH on the pectinolytic activity of flax-retting bacteria

The pectinase produced during the anaerobic retting of flax appeared to have a pH optimum between 5.4 and 5.6. Continuous neutralization during the fermentation, however, induced the production of a pectinase with a pH optimum of 7.1.The majority of the pectin splitting bacteria in the acid and in the neutral retting liquors belonged to the speciesClostridium pectinovorum.Pure culture studies withCl. pectinovorum at fixed pH levels showed that the pectinase produced is adapted to the pH of the environment. No differences in pH dependency could be established between the hemicellulases from the acid and the neutral retting liquor.Although a pH of 6.5 is far from optimal for the hemicellulase, the actual hemicellulolytic activity in the neutral pH retting method is greater than the activity of the normal, acid retting liquor. This fact supports the theory that hemicellulase is responsible for losses in fibre quality and quantity in the neutral pH retting method.