Your browser doesn't support javascript.
loading
Show: 20 | 50 | 100
Results 1 - 20 de 37
Filter
Add more filters










Publication year range
1.
Fungal Genet Biol ; 29(3): 211-20, 2000 Apr.
Article in English | MEDLINE | ID: mdl-10882537

ABSTRACT

To identify the molecular mechanisms of gravitropism in the fungus Phycomyces blakesleeanus we determined several biochemical and physical parameters of paracrystalline protein bodies, so-called octahedral crystals. The crystals, which are present throughout the central vacuoles of the sporangiophore, function as statoliths (Schimek et al., 1999a,b). They possess an average volume of 9.96 microm(3) and a specific mass of 1.26 g cm(-3). SDS-PAGE of purified crystals shows three major proteins with relative molecular masses of 16, 46.5, and 55 kDa. These proteins are absent in gravitropism mutants which lack the crystals. Phototropism mutants (genotype mad) which are graviresponsive (class 1) and those which are defective in gravitropism (class 2) contain the crystals and the three associated proteins. Absorption spectra of isolated crystals and in situ absorption spectra of growing zones indicate the presence of chromophores, probably oxidized and reduced flavins. The flavin nature of the chromophores is also indicated by their fluorescence properties. It appears likely that the chromophores represent an essential part of the statoliths and thus the gravitropic transduction chain.


Subject(s)
Fungal Proteins/chemistry , Fungal Proteins/metabolism , Gravitropism , Phycomyces/chemistry , Phycomyces/growth & development , Crystallization , Electrophoresis, Polyacrylamide Gel , Fungal Proteins/genetics , Fungal Proteins/isolation & purification , Gravitropism/genetics , Molecular Weight , Phototropism , Phycomyces/genetics , Spectrophotometry
2.
Plant Physiol ; 123(2): 765-76, 2000 Jun.
Article in English | MEDLINE | ID: mdl-10859206

ABSTRACT

The interaction between gravitropism and phototropism was analyzed for sporangiophores of Phycomyces blakesleeanus. Fluence rate-response curves for phototropism were generated under three different conditions: (a) for stationary sporangiophores, which reached photogravitropic equilibrium; (b) for sporangiophores, which were clinostated head-over during phototropic stimulation; and (c) for sporangiophores, which were subjected to centrifugal accelerations of 2.3g to 8.4g. For blue light (454 nm), clinostating caused an increase of the slope of the fluence rate-response curves and an increase of the maximal bending angles at saturating fluence rates. The absolute threshold remained, however, practically unaffected. In contrast to the results obtained with blue light, no increase of the slope of the fluence rate-response curves was obtained with near-ultraviolet light at 369 nm. Bilateral irradiation with near-ultraviolet or blue light enhanced gravitropism, whereas symmetric gravitropic stimulation caused a partial suppression of phototropism. Gravitropism and phototropism appear to be tightly linked by a tonic feedback loop that allows the respective transduction chains a mutual influence over each other. The use of tropism mutants allowed conclusions to be drawn about the tonic feedback loop with the gravitropic and phototropic transduction chains. The results from clinostating mutants that lack octahedral crystals (implicated as statoliths) showed that these crystals are not involved in the tonic feedback loop. At elevated centrifugal accelerations, the fluence-rate-response curves for photogravitropic equilibrium were displaced to higher fluence rates and the slope decreased. The results indicate that light transduction possesses a logarithmic transducer, whereas gravi-transduction uses a linear one.


Subject(s)
Gravitropism , Phototropism , Phycomyces/physiology , Light , Mutation , Phycomyces/genetics
3.
Planta ; 210(1): 132-42, 1999 Nov.
Article in English | MEDLINE | ID: mdl-10592041

ABSTRACT

To elucidate the graviperception of the unicellular fungus, Phycomyces blakesleeanus, sporangiophores were inspected for intracellular structures which relocate with respect to gravity. Two structures, paracrystalline proteins (so-called octahedral crystals) and an aggregate of lipid globules, were identified which showed redistribution upon reorientation of the sporangiophore. Octahedral crystals occur throughout the sporangiophore, including the apical growing zone, and are localized inside vacuoles in which they reside singly or in clusters of up to 40 loosely associated individuals. Upon a 90 degrees reorientation of sporangiophores, crystal clusters sedimented in approximately 50-200 s from the upper to the lower side, corresponding to a speed of 0.5-2 micrometers s-1. Stage-4 sporangiophores (with sporangium) of three mutants which lack the crystals displayed anormal kinetics of gravitropism and substantially reduced bending angles in comparison to sporangiophores of the wild type. While horizontally placed wild-type sporangiophores reached the vertical position after 10-12 h, the crystal-lacking mutants bent maximally 40 degrees-50 degrees upward. In stage-1 sporangiophores a conspicuous aggregate of lipid globules is positioned about 50 micrometers below the apex. The globules floated upwards when the sporangiophore was placed horizontally forming in this way a cap-like aggregate. It is proposed that both the sedimenting protein crystals and the upward-floating globules are involved in gravisensing.


Subject(s)
Fungal Proteins/physiology , Gravitropism/physiology , Gravity Sensing/physiology , Phycomyces/physiology , Crystallization , Fungal Proteins/chemistry , Gravitation , Gravitropism/genetics , Gravitropism/radiation effects , Light , Lipids , Mutation , Phycomyces/genetics , Phycomyces/growth & development , Phycomyces/radiation effects , Plastids/physiology , Spores, Fungal/genetics , Spores, Fungal/growth & development , Spores, Fungal/physiology , Spores, Fungal/radiation effects , Vacuoles/physiology
4.
Adv Space Res ; 24(6): 687-96, 1999.
Article in English | MEDLINE | ID: mdl-11542610

ABSTRACT

The sporangiophores of the zygomycete fungus Phycomyces blakesleeanus contain octahedral crystals with diameters of up to 5 micrometers in their vacuole. The crystals are associated with the intracellular membrane system. In tilted or horizontally placed sporangiophores, the crystals sediment to the respective lower face of the vacuole with a velocity of up to 100 micrometers per minute. The sedimentation is completed within about 2 minutes, well within the latency period for the negative gravitropic response of Phycomyces. Crystal-lacking mutant strains display a smaller maximal bending angle and a reduced gravitropic bending rate in comparison to the wild type. We therefore conclude that the crystals serve as statoliths for gravitropism in Phycomyces.


Subject(s)
Fungal Proteins/ultrastructure , Gravity Sensing/physiology , Phycomyces/ultrastructure , Crystallization , Fungal Proteins/chemistry , Gravitropism/genetics , Gravitropism/physiology , Mutation , Phycomyces/chemistry , Phycomyces/genetics , Phycomyces/growth & development , Vacuoles/ultrastructure
5.
Can J Surg ; 32(5): 321, 1989 Sep.
Article in English | MEDLINE | ID: mdl-2766134
6.
Can J Surg ; 31(6): 452-3, 1988 Nov.
Article in English | MEDLINE | ID: mdl-3052767

ABSTRACT

The form of address for British surgeons--"Mister" instead of "Doctor"--has mystified other members of the medical profession for years. The author attempts to show that the designation "Mister" is neither an affectation nor a denigration but a natural consequence of the history of British barbery, barber-surgery and ultimately surgery, resulting from the advice and tutelage of King Henry VIII and Parliament.


Subject(s)
General Surgery/history , Terminology as Topic , History, 15th Century , History, 16th Century , History, 18th Century , History, 20th Century , History, Medieval , United Kingdom
7.
J R Soc Med ; 81(6): 370-1, 1988 Jun.
Article in English | MEDLINE | ID: mdl-20894696
8.
Lancet ; 2(8569): 1220, 1987 Nov 21.
Article in English | MEDLINE | ID: mdl-2890849
9.
J Hand Surg Am ; 12(5 Pt 1): 811, 1987 Sep.
Article in English | MEDLINE | ID: mdl-3655253
11.
Orthop Rev ; 15(4): 261-6, 1986 Apr.
Article in English | MEDLINE | ID: mdl-3453934

ABSTRACT

To sum up: Communication, particularly oral, would be aided or furthered by abstention from cacolalia. Clichés, redundancies, and expressions battered by overuse should be avoided and the imparting of knowledge by means of precise language should be done audibly and at a reasonable speed. One should speak at scientific meetings only as fast and certainly as simply as one would in ordinary mundane intercourse. Above all, one's audience should not know what words or expressions are going to be used in certain given situations. If this could be attained, the hours in a hospital on rounds or at lectures would be better spent and ultimately, the speaker, too, would derive more satisfaction from his work if he were rewarded with stimulating questions from an appreciative audience instead of the perfunctory applause of somnolent, noncomprehending colleagues, driven almost to distraction by unending cacolalia complicated by lightning speed and rank inaudibility.


Subject(s)
Language , Orthopedics , Writing , Humans
13.
Orthop Rev ; 15(3): 190-3, 1986 Mar.
Article in English | MEDLINE | ID: mdl-3331006
14.
J Bone Joint Surg Am ; 67(1): 170, 1985 Jan.
Article in English | MEDLINE | ID: mdl-3968100
15.
Can Med Assoc J ; 133(2): 91-2, 1985 Jul 15.
Article in English | MEDLINE | ID: mdl-20314574
16.
Can Med Assoc J ; 130(4): 349, 1984 Feb 15.
Article in English | MEDLINE | ID: mdl-20314312
17.
Can Med Assoc J ; 128(6): 628, 1983 Mar 15.
Article in English | MEDLINE | ID: mdl-20313871
18.
Can Med Assoc J ; 129(7): 677-8, 1983 Oct 01.
Article in English | MEDLINE | ID: mdl-20313963
19.
JAMA ; 247(24): 3314, 1982 Jun 25.
Article in English | MEDLINE | ID: mdl-7087073
20.
Can Med Assoc J ; 126(8): 900-1, 1982 Apr 15.
Article in English | MEDLINE | ID: mdl-20313717
SELECTION OF CITATIONS
SEARCH DETAIL
...