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1.
Micropropagated bananas derived from Banana Bunchy-Top Virus (BBTV) infected plants, but displaying no symptoms of the disease, were established in the field. They were grown for three years and produced a plant crop and ratoon crops. No disease symptoms were observed. There was uncertainty as to whether
–  micropropagation eliminated the virus from the material,
–  the plants were symptomlessly infected, or
–  the plants were somaclonal variants that suppress symptom expression.
To resolve this question, suckers from these plants and non-infected controls were established in pots and infected with aphids, Pentalonia nigronervosa Coq, collected from BBTV-infected plants. All plants produced characteristic Banana Bunchy-Top Disease (BBTD) symptoms in five months. In addition, samples collected from the original symptomless field plants were tested by DAS-ELISA using a polyclonal antibody specific for BBTV. No detectable levels of virus were found in any of the samples. These studies support the view that the symptomless plants were virus free and not symptomlessly infected or BBTV-resistant somaclones generated from micropropagation. Nevertheless there continues to be a need for caution in dissemination of micropropagated bananas, especially when obtained from regions where BBTV is known to occur.  相似文献   

2.
Thiolutin was found to inhibit the utilization of glucose and other growth substrates in Escherichia coli. The inhibition was detected by a sharp drop of the respiration rate after addition of the antibiotic. The actual function affected was allocated to the cytoplasmic membrane of the bacterial cells by the following evidence:
–  - spheroplasts were affected like intact cells,
–  - individual reactions of either the electron transport chain or the glycolytic pathway were not inhibited,
–  - glucose consumption in the culture stopped and the cells accumulated guanosine tetraphosphate as under starvation conditions,
–  - activation of the cell's apo-glucose dehydrogenase restored respiration via bypassing the glucose phosphotransferase system.
It was concluded that the transport of certain substrates across the membrane was inhibited.  相似文献   

3.
In this report we describe the most suitable protocol for callus formation and plant regeneration for cotton. We screened 15 cotton (Gossypium hirsutum L.) genotypes for metal resistance and two of them, Nazilli M-503 (M503) Nazilli 143 (N-143) selected as Cd, Cu and Ni resistant. The cotyledonary nodes from these genotypes were the best explants for regeneration of shoots (more than 90 %) and roots (50 to 70 %). Shoot apex also gave good shoot regeneration (more than 90 %) but their root regeneration efficiency was low (35 %). These results show that Murashige and Skoog (MS) media containing 0.44 μM naphthaleneacetic acid (NAA) and 0.98 μM indole-3-butyric acid (IBA) was the most suitable recipe for getting high shoot and root regeneration from cotyledonary nodes of N-143 and M503 cotton genotypes.Abbreviations
2,4 D  2,4-dichlorophenoxyacetic acid
BAP  6-benzylaminopurine
GA  gibberellic acid
IBA  indole-3-butyric acid
MS medium  Murashige and Skoog medium
NAA  naphthaleneacetic acid
This work was supported by the Textile Industry grant No. F000301 given to A.R. Memon.  相似文献   

4.
1.  A 28-kDa peptide from the brain of the tobacco hornworm,Manduca sexta, was purifiedvia HPLC. The peptide copurified with the insect neurohormone, prothoracicotropic hormone (PTTH), through two HPLC columns.
2.  Immunocyctochemistry using polyclonal antibodies against the 28-kDa peptide revealed that the peptide was produced in the same protocerebral neurons that produce PTTH. Western blot analysis demonstrated that the 28-kDa peptide and big PTTH are different molecules.
3.  A PTTHin vitro bioassay indicated that despite having chromatographic properties similar to those of big PTTH and being produced by the same neurons, the 28-kDa peptide did not have PTTH activity.
4.  Amino acid sequence analysis yielded a 27 N-terminal amino acid sequence that had no similarity with known peptides.
5.  Immunocytochemical studies revealed that the 28-kDa peptide is present as early as 30% embryonic development and is absent by adult eclosion. This is in contrast to big PTTH, which is expressed throughout theManduca life cycle.
6.  These data suggest that the 28-kDa peptide is another secretory phenotype of the lateral neurosecretory cell group III (L-NSC III) which may have functions distinct from those for big PTTH or may act synergistically with big PTTH.
  相似文献   

5.
Path analysis was used to determine the importance of long-term disturbance regime and the relative importances of correlations among vegetation patterns, disturbance history, and nitrogen (N) mineralization in old-growth forests of northwestern Minnesota. Leaf biomass (estimated by allometric equations), fire history (from fire scars on Pinus resinosa trees), and N mineralization rates (estimated from incubationsin situ) were determined from sample plots dominated by
–  Betula papyrifera, Populus tremuloides, andP. grandidentata
–  a mixture ofAcer saccharumandTilia americana, or
–  Quercus borealis andOstrya virginiana.
  相似文献   

6.
1.  We used laser vibrometry and free field sound stimulation to study the frequency responses of the eardrum and the lateral body wall of awake male Eleutherodactylus coqui.
2.  The eardrum snowed one of two distinct frequency responses depending on whether the glottis was open (GO response) or closed (GC response) during the measurement.
3.  The lateral body wall vibrated with a maximum amplitude close to that of the eardrum and in the same frequency range.
4.  Covering the frog's body wall with vaseline reduced the vibration amplitude of the GC response by up to 15 dB.
5.  When a closed sound delivery system was used to stimulate a local area of the body wall the eardrum also showed one of two types of responses.
6.  These results suggest that sound is transmitted via the lung cavity to the internal surface of the eardrum. This lung input has a significant influence on the vibrations of the eardrum even when the glottis is closed.
7.  The vibration amplitude of the eardrum changed with the angle of sound incidence. The directionality was most pronounced in a narrow frequency range between the two main frequencies of the conspecific advertisement call.
  相似文献   

7.
G. Rombi  G. Piu  S. Piro  V. Anedda 《Cytotechnology》1993,11(Z1):S147-S149
Being able to carry zidovudine (AZT) at known concentrations into CD4+/CD38+ and CD14+ cells permits:
–  - to reduce the drug dosage and to increase the interval for administration (until 1 dose I.V. every week);
–  - to modulate the drug concentration into the CD4+/CD38 an CD14+ cells in relation to the in vitro determined HIV sensitiveness;
–  - to eliminate haematological, medullary and general toxicity;
–  - to be able to treat severely hill patients.
Further studies are necessary in order to:
–  - To find out the better phase to start the therapy;
–  - To use several drugs with different mechanisms of action in order to slow down as much as possible the presence of resistant viral strains.
–  - As for other drugs which are beginning to be used with artificial vehicles, futher studies are required to improve the selectivity and safety of LIPOAZT for the target cells including macrophages.
  相似文献   

8.
1.  We have obtained a cDNA clone encoding a human retinal D2 dopamine receptor.
2.  The longest open reading frame (1242 bp) of this clone encodes a protein of 414 amino acids having a predicted molecular weight of 47,000 and a transmembrane topology similar to that of other G protein-coupled receptors.
3.  Transient transfection of COS-7 cells with an expression vector containing the clone resulted in expression of a protein possessing a pharmacological profile similar to that of the D2 dopamine receptor found in striatum and retina.
4.  Northern blot analysis indicated that, in rat brain and retina, the mRNA for this receptor was 2.9 kb in size.
5.  In situ hybridization was performed to examine the distribution of the mRNA for this receptor in human retina. Specific hybridization was detected in both the inner and the outer nuclear layers.
6.  These findings are consistent with prior physiological and autoradiographic studies describing the localization of D2 dopamine receptors in vertebrate retinas. Our observations suggest that photoreceptors as well as cells in the inner nuclear layer of human retinas may express the mRNA for this D2 dopamine receptor.
  相似文献   

9.
Phytoplanktonic populations were studied in Tazenat lake by three methods:
–  Primary production using 14C technic
–  Standing crop estimation
–  Amount of chlorophyll a
A comparison of the results obtained gives an insight into the utilisation and transformation of energy by the biota of the lake  相似文献   

10.
1.  Transepithelial potential differences (PDte) and acidification rates of the bath chamber were measured on isolated perfused posterior gills of the fiddler crabUca tangeri adapted to dilute seawater.
2.  The PDte decreased to almost zero when Na+ was substituted by choline or when ouabain was added to the perfusion saline in high concentrations (10 mmol·l–1). Thus, the rheogenic NaCl-transport across the gill epithelium seems to be totally Na+-dependent.
3.  When Cl– was replaced by gluconate, a bath positive PDte occurred which was insensitive to ouabain. This PDte could also be observed when, in addition to Cl– removal, Na+ was replaced by TMA+.
4.  Bath acidification under normal conditions could be abolished by ouabain, indicating that there is H+ excretion via electrically silent Na+/H+ exchange. In contrast, bath acidification under Cl–-free conditions is only partially blocked by ouabain.
5.  It is concluded that under Cl–-free conditions a rheogenic H+-pump in the apical membrane is responsible for the ouabain-insensitive bath acidification as well as for the PDte.
Parts of this study had been published earlier in abstract form  相似文献   

11.
(1)  The influence of sheep grazing of moderate grazing (MG), heavy grazing (HG), inordinate grazing (IG), over grazing (OG), and extinct grazing (EG) on vegetation succession was studied in the Stipa baicalensis steppe during 1984–1986.
(2)  The relationships between the relative sum of dominance ratio (RSDR) and the degree of succession (DS) at all stages of grazing succession in the Stipa baicalensis steppe were revealed in terms of the method of mathematical analysis under five grazing intensities mentioned above.
(3)  The dynamic models of grazing succession that are based on accurate grazing intensities in relation to succession courses were constructed using RSDR5, and DS. The models may explain the rules of grazing succession in the Stipa baicalensis steppe.
  相似文献   

12.
The caudal photoreceptors (CPRs) of crayfish (Procambarus clarkii) can trigger walking and abdominal movements by their response to light.
1.  In a restrained, inverted crayfish, illumination of A6 evoked a CPR discharge followed by leg movements and bursting from the abdominal tonic flexor (TF) motoneurons. Intracellular electrical stimulation of a single CPR at high frequency (80 Hz) evoked similar responses.
2.  Responses only occurred when a single CPR axon was driven at 60 Hz or more and outlasted the stimulus.
3.  CPR stimulation also excites the pattern-initiating network (Moore and Larimer 1987) in the abdomen.
4.  The axon of the CPR projects from ganglion A6 to the brain. Terminal branches occur in the subesophageal ganglion and the brain. A small descending interneuron is dye-coupled to CPR in the subesophageal ganglion.
5.  In animals with cut circumesophageal connectives, the CPRs can evoke walking and the abdominal motor pattern.
6.  The relationship of the abdominal motor pattern to walking is altered by restraint and/or inversion. In freely moving crayfish, the cyclic abdominal motor pattern is only observed with backward walking. In restrained, inverted crayfish, the motor pattern occurs with both forward or backward walking.
  相似文献   

13.
Several species of weakly electric fish reflexively change their frequency of electric organ discharge (EOD) in response to sensing signals of similar frequency from conspecifics; that is, they exhibit jamming avoidance responses (JAR).Eigenmannia increases its EOD frequency if jammed by a signal of lower frequency and decreases its EOD frequency if jammed by a signal of higher frequency. This discrimination is based on an analysis of the patterns of amplitude modulations and phase differences resulting from signal interference. Fish of the closely related genus,Sternopygus, however, do not exhibit a JAR. Here we show that despite lacking this behavior,Sternopygus shares many sensory processing capacities withEigenmannia:
1.  Fish could be conditioned to discriminate the sign of the frequency difference (Df) between an exogenous sinusoidal signal and its own EODs with as few as 300 training trials.
2.  Fish can discriminate the sign of Df for jamming signals with an amplitude as low as 2 V/cm (p-p); which is approximately 40 dB below the amplitude of the fish's EOD, as measured lateral to the operculum.
3.  Fish appear to discriminate the sign of Df by evaluating modulations in signal amplitude and differences in the timing of signals received by different areas of the body surface.
4.  Sternopygus processes electrosensory information through band-pass modulation filters. Tuning to modulation rates over at least 4–16 Hz exists.
  相似文献   

14.
The present review describes the effects of light on reproductive processes in fungi, mainly when action spectra are available.The study of these has resulted in three kinds of photoresponses observable in fungi:
–  responses only to UV light (230–380 nm)
–  responses to NUV and blue light (300–520nm)
–  responses to great wavelengths of the visible spectrum. The photomorphogenetic processes on the control of these same photoreceptor pigments are reviewed.
  相似文献   

15.
1.  The effects of three barbiturates and the local anesthetic procaine on the ion channel function of mouse nicotinic acetylcholine receptor (nAChR) muscle subtype expressed inXenopus laevis oocytes were examined by whole-cell voltage-clamp technique.
2.  A concentration-response curve for the specific nicotinic agonist dimethylphenylpiperazinium iodide (DMPP) was first determined. This agonist produced increasing whole-cell currents up to a concentration of 100µM (EC50 = 13µM), then decreased responses at higher concentrations.
3.  The barbiturates (amobarbital, secobarbital, pentobarbital) and procaine produced reversible inhibition of DMPP-induced currents at clinically used concentrations. The two classes of drugs differed in the voltage dependence of the inhibition: procaine-induced inhibition was increased at more negative transmembrane holding potentials (-90 vs. -45 mV); whereas amobarbital-induced inhibition did not vary at different transmembrane potentials.
4.  Mutant forms of the nAChR, containing single amino acid changes in the M2 regions of and subunits, showed increased sensitivity to procaine but no change in sensitivity to amobarbital-induced inhibition.
5.  These electrophysiologic studies provide further evidence that barbiturates and local anesthetics produce inhibition of the nAChR at different sites.
  相似文献   

16.
1.  In this commentary we discuss results obtained by a micromethod for the study of Cl– permeability across single nerve membranes from rabbit Deiters' neurons.
2.  These results showed the presence of GABAA receptors on the nerve cell membrane cytoplasmic side.
3.  We could show that these receptor complexes have a higher affinity for GABA than their extracellularly facing counterparts. Moreover, they present a phenomenon of desensitization. Another distinct property is that upon activation by GABA, they expose positive charges at their cytoplasmic mouths.
4.  We propose that these receptor complexes could functionin situ as a device for extruding Cl– anions from the nerve cell interior. This phenomenon would create an electrochemical gradient for Cl– penetration into the cell upon the action of extracellular GABA, after its presynaptic release.
  相似文献   

17.
Glycolytic intermediates and related metabolites were measured in the fat body of the American cockroach (Periplaneta americana) to locate the rate-limiting reactions that regulate glycolysis during the action of the corpus cardiacum (CC) in vitro.
1.  The concentrations of glucose 1-phosphate, fructose 6-phosphate, and fructose 1,6-bisphosphate were approximately doubled after 30 min treatment with CC extract, whereas that of glucose 6-phosphate increased more than four-fold. Slightly lower increases occurred after 10 and 60 min treatment.
2.  Triose phosphates, 2-phosphoglyceric acid, phosphoenolpyruvate and pyruvate were unaffected by CC extract.
3.  Glycerol 3-phosphate, which is 20\2-200 times more concentrated than any of the other measured metabolites in the unstimulated tissue, is increased more than two-fold by CC extract.
4.  NAD, NADP, and ATP were not significantly affected by CC extract. ADP was increased significantly by the gland extract.
  相似文献   

18.
1.  By penetrating axons in the ventral nerve cord of the dragonfly, Aeshna umbrosa, we measured the intracellular responses of target-selective visual interneurons to movement of black square targets ranging from 1° to 32° visual angle at several levels of mean background luminance.
2.  Neuronal responses, measured both in number of spikes and in the magnitude of integrated postsynaptic potentials, showed a preference for larger target size at lower mean luminance (Table 1, Figs. 1–3). The latency of postsynaptic potential (psp) and spike responses from onset of target movement increased with a decrease in mean luminance (Fig. 1).
3.  A measure of mean target size preference (Eqn. 1) for one identified interneuron (MDT4) in both laboratory and outdoor lighting shows a continuous decrease of preferred size with increases of mean luminance over more than 4 orders of magnitude.
4.  The time to reach the new steady state of cell response after the decrease of mean luminance was ordinarily less than 30 s, but sometimes longer (Fig. 4).
  相似文献   

19.
Methyl jasmonate (JA-Me) promoted leaf abscission of succulent plant, Crassula lycopodioides, and exudation from stems and leaves after leaf abscission when it was sprayed in whole plants. Major component of the exudate was identified as sucrose based on the results described below.
(1)  The reaction of the excudate was not positive in the Somogyi-Nelson method but in the phenol-sulfuric acid method.
(2)  The exudate was hydrolyzed with invertase of Candida utilis, after that showing a positive reaction in the Somogyi-Nelson method.
(3)  Only glucose and mannose were identified in the exudate after hydrolysis with trifluoroacetic acid using a gas-liquid chromatograph (GLC).
(4)  A single peak corresponding to the retention time of sucrose was observed using a high performance liquid chromatograph (HPLC).
In addition, potassium and sodium were found in the exudate as major inorganic cations. These results suggest that exudate of Crassula lycopodioides is phloem sap, and JA-Me promotes the excudation due to the inhibition of the synthesis of callose in sieve tubes of succulent plants.  相似文献   

20.
1.  The reactions of tympanic nerve fibers ofLocusta migratoria were recorded by glass microelectrodes in the metathoracic ganglion.
2.  The units were classified by frequency-, intensity-, and directional characteristics as well as by their response pattern. The response to speciesspecific song is compared with the response to song ofEphippiger ephippiger.
3.  The physiological properties lead to a classification into three types of low-frequency neurons (characteristic frequency 3.5–4 kHz; 4kHz; 5.5–6 kHz) and one type of high-frequency neuron (12–20 kHz). This is similar to other species (Gray, 1960, Michelsen, 1971).
4.  Intensity-coding is done by sharp rising intensity characteristics and by different absolute thresholds of the units.
5.  There is a marked directional sensitivity with some differences between LF and HF units. In the low frequency range the tympanal organ seems to react as a pressure gradient receiver; for high frequencies another mechanism is discussed.
6.  No filtering of species-specific song takes place at the level of the receptor cells.
  相似文献   

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