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PubMed2000

Cycloheximide-induced inhibition of chitin synthesis, and decay of apical vesicles and chitosomes in Phycomyces blakesleeanus.

Addition of cycloheximide rapidly inhibited protein synthesis in Phycomyces blakesleeanus. In contrast, chitin biosynthesis decreased with biphasic kinetics displaying a slow and a rapid decay phases. Electron microscopic studies revealed a decrease in the number of apical vesicles and chitosomes after cycloheximide addition; and no change in wall thickness. It is proposed that the slow phase of decay in chitin biosynthesis represents the exhaustion of the pool of chitosomes which transport the chitin synthase necessary to maintain apical wall growth; whereas the second one corresponds to inactivation of the enzyme, which is short lived in vivo. Data also rule out a change in the polarization of wall synthesis induced by cycloheximide, as suggested in other systems.

Antifungal Agents↗
PubMed2004

A transplasma membrane redox system in Phycomyces blakesleeanus: properties of a ferricyanide reductase activity regulated by iron level and vitamin K3.

Intact Phycomyces blaskesleeanus mycelia are capable of reducing extracellular ferricyanide and this transmembrane reduction is an enzymatic process, which is enhanced by the presence of 10 mM lactate. It is modulated in response to intracellular iron levels and negatively regulated by iron and copper. It is inhibited by NEM, p CMB, iodoacetate, Zn2+, Cd2+, dicumarol, and capsaicine analog, but not by cloroquine, and activated by Ca2+, Mg2+, Na+, and K+. Ferricyanide reduction was concomitant with proton release into the extracellular medium, both processes being greatly promoted by vitamin K3 following hyperbolic saturation kinetics with regard to ferricyanide concentration. No stoichiometric proton release was observed with regard to ferricyanide reduction in the absence or the presence of vitamin K3. Proton release coupled with ferricyanide reductase activity does not appear to be due to H+-ATPase. The relevance of these findings to the relationship between the two processes is discussed.

Cell Membrane↗
PubMed1975

Meiosis in Phycomyces.

A four-factor cross between two strains of Phycomyces involving two auxotrophic, one color, and the mating type marker is described. Samples of 40 germspores from 84 individual fertile germsporangia were characterized. The results show: (i) The germspores of a germsporangium are derived from one meiosis in approximately 78% of the cases. (ii) The four markers are on separate chromosomes. They are nonselective. (iii) Analysis of a large sample of germspores from 106 pooled germsporangia confirms that the four markers are unlinked. (iv) From the ditype/tetratype ratios it is inferred that each marker is located about 15 map units from its centromere.

Alleles↗
PubMed1976

Responses of Phycomyces indicating optical excitation of the lowest triplet state of riboflavin.

Phototropic and light growth responses of the sporangiophore of Phycomyces have been elicited using tunable laser stimulation from 575 to 630 nm. The growth response shows additional components of the action spectrum with a sharp peak at 595 nm, a sharp cut-off at 585 nm, and a tail extending beyond 630 nm. The integral over the electronic transition (f-value) is 1.5 X 10(-9) times that at 455 nm. These parameters indicate a direct transition from the ground state to the lowest triplet state of riboflavin.

Fungi↗
PubMed2004

Gravitropism in Phycomyces: threshold determination on a clinostat centrifuge.

The absolute sensitivity of sporangiophores of Phycomyces blakesleeanus to centrifugal acceleration was determined on a clinostat centrifuge. The centrifuge provides centrifugal accelerations ranging from 10(-4) to 6 x g. The rotor of the centrifuge, which accommodates 96 culture vials with single sporangiophores, is clinostatted, that is, turning "head over", at slow speed (1 rev min(-1)) while it is running. The negative gravitropism of sporangiophores is characterized by two components: a polar angle, which is measured in the plane of bending, and an aiming-error angle, which indicates the deviation of the plane of bending from the vector of the centrifugal acceleration. Dose-response curves were generated for both angles with centrifugations lasting 3, 5, and 8 h. The threshold for the polar angle depends on the presence of statoliths, so-called octahedral protein crystals in the vacuoles. The albino strain C171 carAcarR (with crystals) has a threshold near 10(-2) x g while the albino strain C2 carAgeo-3 (without crystals) has a threshold of about 2 x 10(-1) x g. The threshold for the aiming error angle is ill defined and is between 10(-2) and 10(-1) x g. The threshold for the polar angle of the wild type NRRL 1555 (with crystals) is near 8 x 10(-2) x g.

Centrifugation↗
PubMed1959

Photo-reactions in Phycomyces; growth and tropic responses to the stimulation of narrow test areas.

Sporangiophores of Phycomyces in stage IV b have been stimulated by parallel light in test areas 0.2 mm. wide. The growth responses to large stimuli are very large, owing probably to light scattered within the specimen. For medium stimuli the sensitive zone coincides with the growth response zone obtained previously and excludes the region of maximum stretch. Sustained stimulations were used to elicit tropic responses. The bends formed travel away from the sporangium at a speed equal to the growth speed. Thus they remain very close to the stimulus when this is held at a constant level relative to ground but separate from it for stimuli programmed differently. The existence of a protoplasmic structure, the "inner wall," with the following properties is postulated: it is attached to the lower, non-growing part of the sporangiophore and grows by addition above the sensitive zone. It neither stretches nor twists in the sensitive zone. It is the seat of the light receptors and gives growth and tropic responses. The cell wall follows its bends by elastic stretch.

Cytoplasm↗
PubMed1961

Photoreactions in Phycomyces. Responses to the stimulation of narrow test areas with ultraviolet light.

Equipment has been developed for ultraviolet illumination of sharply bounded test areas of the growing zone of sporangiophores of Phycomyces. The growing zone is opaque for this light and the tropic responses are negative. Periodic short narrow stimuli on alternating sides produce periodic tropic responses when applied at x > 0.5 mm, but none for x < 0.5 mm, where x is the distance below the sporangium. Sustained tropic stimuli, applied at constant x, produce tropic responses for any x > 0.1 mm. The lag between stimulus and response is 3.3 min. for any x > 0.5 mm. For smaller x the lag increases progressively. In all cases the tropic bend occurs at values of x > 0.5 mm. Sustained tropic stimuli, applied at constant height relative to ground, produce relatively sharp tropic bends. The center of the bend is at all times close to the simultaneous position of the stimulated area. The boundaries of a light-adapted zone move less than 0.1 mm in 10 min. relative to the sporangium. It is concluded that the receiving and adapting structures do not move relative to the sporangium, and that the responding system does not move relative to ground. The two systems move relative to each other with the speed of growth. The responding system does not extend above x = 0.5 mm.

Fungi↗
PubMed1961

Tropic responses of Phycomyces sporangiophores to gravitational and centrifugal stimuli.

A low-speed centrifuge was used to study the tropic responses of Phycomyces sporangiophores in darkness to the stimulus of combined gravitational and centrifugal forces. If this stimulus is constant the response is a relatively slow tropic reaction, which persists for up to 12 hours. The response is accelerated by increasing the magnitude of the gravitational-centrifugal force. A wholly different tropic response, the transient response, is elicited by an abrupt change in the gravitational-centrifugal stimulus. The transient response has a duration of only about 6 min. but is characterized by a high bending speed (about 5 degrees /min.). An analysis of the distribution of the transient response along the growing zone shows that the active phase of the response has a distribution similar to that of the light sensitivity for the light-growth and phototropic responses. Experiments in which sporangiophores are centrifuged in an inert dense fluid indicate that the sensory mechanism of the transient response is closely related to the physical deformation of the growing zone caused by the action of the gravitational-centrifugal force on the sporangiophore as a whole. However, the response to a steady gravitational-centrifugal force is most likely not connected with this deformation, but is probably triggered by the shifting of regions or particles of differing density relative to one another inside the cell.

Fungi↗
PubMed1961

Interplay between the reactions to light and to gravity in Phycomyces.

Sporangiophores of Phycomyces do not grow directly towards a horizontal beam of light, but equilibrate at an angle of about 30 degrees above the horizontal. After describing several related observations, this paper suggests that the dioptric properties of an obliquely illuminated cylindrical lens, illustrated by a dummy cell, as well as a negative geotropic response, play major roles in determining the direction of growth. The shift of the equilibrium direction of growth towards the vertical, or a purely geotropic response, over a tenfold range of very low intensities (around 10(6) quanta/cm(2) sec., or 10(-13)watt/cm(2)) has been studied, and an action spectrum made, measuring the quantum fluxes producing a standard intermediate equilibrium direction of growth at different wavelengths. This may differ from the action spectra at higher intensities in lacking conspicuous maxima from 370 to 490 mmicro. However, in the ultraviolet it parallels the other spectra, although without showing the much higher quantum efficiency of ultraviolet relative to visible light previously noted. Possible interpretations are discussed.

Fungi↗
PubMed1964

THE EFFECT OF LIGHT ON THE GEOTROPIC RESPONSES OF PHYCOMYCES SPORANGIOPHORES.

The geotropic responses of Phycomyces sporangiophores were studied under varying intensities of illumination, using a low speed centrifuge and a fixed beam of blue light. This light has a strongly inhibitory effect on the transient geotropic response, reducing it to 36 per cent of its magnitude in darkness. The inhibition does not vary systematically with light intensity over a range of 400-fold. The light sensitivity of the transient geotropic response thus differs from the light-growth response system, which shows the same growth rate in light and darkness. By contrast, the slower long term geotropic response is enhanced by light of moderate intensities, but is strongly inhibited by high intensities. At and above a mean intensity of about 1 microw/cm(2), the long term response is completely removed. If the intensity is lowered from an inhibitory level, either to darkness or to a low level, the geotropic response appears after a time lag of 20 minutes. Furthermore an increase in intensity from one level to another, both levels normally enhancing, results in a transient reversal in the long term geotropic response, also after a time lag of 20 minutes. Thus it is suggested that light is acting at some intermediate step in the long term geotropic sensory system, a step that normally requires 20 minutes for completion.

Fungi↗
PubMed1965

STEADY-STATE PHOTOTROPISM IN PHYCOMYCES.

The steady-state phototropic bending of Phycomyces sporangiophores was studied using apparatus designed to keep the growing zone vertical and the angle of illumination constant over long periods of time. The bending speed is quite constant if the intensity and angle of illumination are fixed. A phototropic inversion occurs in response to a sudden change in intensity, either an increase or a decrease. A bending component lateral to the illumination direction is strongly evident at normal incidence. It is shown that this component is due to a rotation between the stimulus and response loci about the axis of the growing zone, which is probably related to the spiral growth of the cell. The steady-state bending speed is at a maximum value for illumination directions ranging from normal incidence to about 45 degrees . From 45 to 14 degrees the bending speed decreases linearly with angle, reaching zero at 14 degrees . Angles less than 14 degrees elicit a weak negative phototropic response. Using an optical model of the growing zone, the intracellular intensity distribution was determined as a function of the angle of illumination. Several hypotheses relating the intensity distribution to the phototropic response are discussed.

Biophysical Phenomena↗
PubMed1975

Avoidance response, house response, and wind responses of the sporangiophore of Phycomyces.

Avoidance response: An object placed 1 mm from the growing zone of a Phycomyces sporangiophore elicits a tropic response away from the object. The dependence of this response on the size of the object and its distance from the specimen is described, as well as measurements which exclude electric fields, electromagnetic radiation, temperature, and humidity as avoidance-mediating signals. This response is independent of the composition and surface properties of the object and of ambient light. House Response: A house of 0.5- to 10-cm diameter put over a sporangiophore elicits a transient growth response. Avoidance responses inside closed houses are slightly smaller than those in the open. Wind responses: A transverse wind elicits a tropic response into the wind, increasing with wind speed. A longitudinal wind, up or down, elicits a transient negative growth response to a step-up in wind speed, and vice versa. It is proposed that all of the effects listed involve wind sensing. This proposal is supported by measurements of aerodynamic effects of barriers and houses on random winds. The wind sensing is discussed in terms of the hypothesis that a gas is emitted by the growing zone (not water or any normal constituent of air), the concentration of which is modified by the winds and monitored by a chemical sensor. This model puts severe constraints on the physical properties of the gas.

Fungi↗
PubMed1981

Phycomyces: irregular growth patterns in stage IVb sporangiophores.

Net rotation and net elongation of a stage IVb Phycomyces growing zone were simultaneously measured minute by minute with a photographic apparatus coupled with a rotating stage. A direct correlation between a growth response and a twist response after either a light stimulus or a house stimulus was found. There were significant irregularities in growth rate in both the elongation and rotation that were not a result of measurement error; these irregularities were poorly, if at all, correlated. We believe that these fluctuations reflect the underlying molecular mechanism of cell wall synthesis.

Fungi↗
PubMed1984

Threshold and adaptation in Phycomyces. Their interrelation and regulation by light.

The absolute light sensitivity of Phycomyces sporangiophores was determined by analyzing the intensity dependence of the phototropic bending rate and of the light growth and dark growth responses to step changes of the intensity. We found that the different methods give approximately the same results for the wild-type strain, as well as for several behavioral mutants with defects in the genes madA, madB, and madC. A crucial factor in the determination of thresholds is the light intensity at which the strains grow during the 4 d after inoculation and prior to the experiment. When the wild-type strain grows in the dark, its threshold for the bending rate is 10(-9) W X m-2, compared with 2 X 10(-7) W X m-2 when it is grown under continuous illumination. Further, the maximal bending rate is twice as high in dark-grown strains. This phenomenon is further complicated by the fact that the diameter and growth rate of the sporangiophores also depend on the illumination conditions prior to the experiment: light-grown sporangiophores have an increased diameter and an increased growth rate compared with dark-grown ones. Some of the behavioral mutants, however, are indifferent to this form of light control. Another factor that is controlled by the growth conditions is adaptation: the kinetics of dark adaptation are slower in light-grown sporangiophores than in dark-grown ones. We found empirically a positive correlation between the slower dark adaptation constant and the threshold of the bending rate, which shows that the two underlying phenomena are functionally related.

Dark Adaptation↗
PubMed1984

Phycomyces: detailed analysis of the anemogeotropic response.

Stage IVb sporangiophores of Phycomyces grow into the wind--the anemotropic response--and away from gravity--the geotropic response. A procedure has been designed to measure the equilibrium bend angle that results when the two stimuli are given simultaneously over a long period of time. This angle will be referred to as the anemogeotropic equilibrium angle. This measurement of a sensory response is analogous to the photogeotropic equilibrium angle in which the variable stimulus is light instead of wind. We have found that the anemogeotropic angle, measured relative to the vertical, increases with both increasing wind speed and increasing relative humidity of the wind stimulus. This finding is new and argues against a major prediction of the mass transfer model that anemogeotropism and relative humidity are inversely related. Data from these anemogeotropic experiments further suggest that the self-emitted gas responsible for both the anemotropic response and the avoidance response is water.

Air Movements↗
PubMed1984

The gravireceptor of Phycomyces. Its development following gravity exposure.

The gravitropism of a mature stage IV Phycomyces sporangiophore has a shorter and more uniform latency if the sporangiophore is exposed horizontally to gravity during its earlier development (stage II and stage III). This early exposure to an altered gravitational orientation causes the sporangiophore to develop a gravireceptor as it matures to stage IV and resumes elongation. A technique has been developed to observe the spatial relationship between the vacuole and the protoplasm of a living sporangiophore and to show the reorganization caused by this exposure to altered gravity. Possible gravireceptor mechanisms are discussed.

Cytoplasm↗
PubMed1986

A BASIC program on heterokaryosis and survival in Phycomyces.

We have written a BASIC program about survival and heterokaryosis in Phycomyces for APPLE II series. Surviving and heterokaryotic unit fraction of spores as a consequence of several lethal effects such as mitotic, dominant and recessive lethals can be computed by the system, and also the uninucleate fraction of spores which were originated by mitotic and recessive lethals. The probability of a mitotic lethal per nucleus can be also computed starting from the only surviving unit fraction of spores. The program can also compute the relationship between the mutation rates due to mitotic and recessive lethals acting together concurrently, introducing surviving and heterokaryotic unit fraction of spores. The program can be easily modified to run on different microcomputers with similar versions of BASIC.

Algorithms↗
PubMed1985

Developmental modulation of DNA methylation in the fungus Phycomyces blakesleeanus.

DNA methylation is a rather sparse event among fungi. Phycomyces blakesleeanus seems to be one of the few exceptions in this context. 5-Methylcytosine represents 2.9% of the total cytosine in spore DNA and is located in approximately the same amount at any of the four CA, CT, CC or CG dinucleotides. A progressive and gradual drop in total 5-methylcytosine parallels the development of the fungus. This demethylation is non random but sequence specific and is not accounted for equally by the four different methylated dinucleotides, CG being much less affected (20% demethylated) than CA, CT and CC (more than 90% demethylated at the same time). "De novo" methylation to restore the initial pattern probably takes place during spore maturation. By using specific hybridization probes we have been able to show that the rRNA genes are not significantly methylated at any stage of development, regardless of their transcription status.

5-Methylcytosine↗