Effects of light and temperature on sporangiophore initiation in Pilobolus crystallinus (Wiggers) Tode

Sporangiophore initiation in Pilobolus crystallinus grown in white light was induced by either a dark or a low-temperature treatment. The period of darkness necessary to induce sporangiophore initiation was shortened by lowering the temperature. Arrhenius plots for the sporangiophore-suppressing reaction in both light and darkness consisted of two straight lines with a Q₁₀ of about 2 at lower temperatures and 8–11 at higher temperatures. The temperature at which the Q₁₀ changed was the lower, the higher the fluence rate: 14° C at 8 W/m², 19.5° C at 0.24 W/m² and 24.5° C in darkness. Possible interpretations of these results are briefly presented.Abbreviations %SP percentage of trophocysts initiating sporangiophores - D50% duration of treatment required to 50% sporangiophore initiation     

Photomorphogenesis inPhycomyces: Dependence on environmental conditions

The production of two kinds of vegetative reproductive structures, microphores and macrophores, byPhycomyces blakesleeanus Bgff. depends on plating density, ventilation, asparagine supply, and illumination. Quantitative determinations of these variables lead us to propose a new experimental system for developmental photobiology: standard plastic Petri plates containing 25 ml minimal medium are inoculated with 10⁵ viable, heat-activated spores and incubated, unpiled and unsealed, at 22° C. After 4 d microphores are counted and macrophores are weighed. Both microphorogenesis and macrophorogenesis are governed by light. Photosensitivity is a developmental phenomenon which occurs 32 to 68 h after inoculation, just before the beginning of vegetative reproduction in the dark controls. The maximum photosensitivity occurs 48 h after inoculation.     

Parameters governing gravitropic response of sporangiophores inPhycomyces blakesleeanus

The sporangiophores (spphs) of the fungusPhycomyces blakesleeanus bend upward in a negative gravitropic response when placed in a horizontal position in the dark. The spphs of a hypergravitropic mutant showed higher bending rate and shorter latency period than those of the wild type. In both strains, spphs of smaller diameter had higher bending rates. No significant differences were found between the wild type and the mutant and between the thin spphs and the spphs of standard diameter in respect to their elongation rates. Phototropic rate was also the same between the wild type and the mutant. Parameters influencing the gravitropic response such as diameter of the spph, absolute elongation rate, and ratio of differential growth between the upper and the lower sides of the extension zone of spph were investigated to elucidate the kinetics of bending in the mutant. The results demonstrate that the rapid gravitropic response in the mutant is due to its higher (about 5–6 times) differential-growth rate compared with the wild type.     

Photomorphogenesis inPhycomyces: Fluence-response curves and action spectra

Blue light regulates vegetative reproduction inPhycomyces blakesleeanus Bgff. by inhibiting the development of microphores and stimulating that of macrophores. Fluence-response curves were obtained at twelve different wavelengths. Each response exhibits a two-step (biphasic) dependence on fluence, as if it resulted from the addition of two separate components with different thresholds, midpoints, and amplitudes. The absolute threshold is close to 10 photons·m². The threshold fluence of the low-intensity component is about 10⁴ times smaller than that of the high-intensity component. The action spectra for each of the two components of the two responses share general similarities, but exhibit significant differences that might be taken to favour four separate photosystems. Additional complexity is indicated by the wavelength dependence of the saturation levels.     

The Phycomyces lens: measurement of the sporangiophore intensity profile using a fiber optic microprobe

A fiber optic microprobe, 5.5 m in diameter, was used as a detector to measure the light intensity profile at the distal cell surface of Phycomyces blakesleeanus (Burgeff) sporangiophores that were irradiated unilaterally by a collimated xenon source. The light intensity at a fixed location of the cell surface showed large random variations over time which were probably the result of optical effects of particles being carried past the probe by cytoplasmic streaming. The intensity profile, formed around the distal periphery of the cell by the lens action of the sporangiophore, was determined from intensity measurements made while the probe was held fixed and the incident beam direction was varied in angle of azimuth. The resulting profile consisted of two steeply rising sides enclosing a central plateau or shallow well which ranged in fluence rate from 1.6 to 2.2 times that of the incident beam. These experimental findings differ from theoretical modeling where much greater contrast between the sides and central portion of the lens profile was predicted. These results also indicate that the mechanism of phototropic sensory perception in Phycomyces may filter out cytoplasmic light flicker and may not require strong contrasting regions within the lens profile to detect light direction.     

Relationship of photocarotenogenesis to other behavioural and regulatory responses inPhycomyces

The effect of light on carotene accumulation was studied by analyzing the -carotene content of 4--old mycelia continuously exposed to illumination of different intensities. The wild-type, mutants defective in phototropism, mutants defective in carotene regulation, and newpic mutants specifically defective for photocarotenogenesis were examined. The results indicate that photocarotenogenesis depends on a single sensory pathway which shares its earlier steps (governed by genesmadA andmadB) with the sensory pathway for phototropism. It shares its later steps (probably governed by genescarA andpicB) with one of the pathways for carotene regulation, and includes at least one specific step (governed by genepicA) not known to be involved in other responses.     

Phototropic fluence-response curves for Pilobolus crystallinus sporangiophore

Fluence-response relationships were examined for positive and negative phototropism induced by blue (450 nm) and ultraviolet-B (UV-B, 280 nm) light, respectively, in the Pilobolus crystallinus sporangiophore. Fluence-response curves for both blue and UV-B light obtained by changing the fluence by varying exposure time only showed the classical first and second positive bending. However, fluence-response curves obtained by varying the fluence rate were bell-shaped irrespective of the length of the exposure time. With increasing exposure time the peak became higher along the ascendant arm and the descendant arm was shifted toward the higher fluence. The Bunsen-Roscoe reciprocity law was valid only when the fluence was less than approx. 400 pmol·m^-2 for both blue and UV-B light. Because the shapes of the fluence-response curves for blue and UV-B light were nearly the same, the photoreceptor systems for both blue and UV-B light are considered to be the same.Abbreviation UV-B ultraviolet-B     

Growth-rate adaptation of Phycomyces sporangiophores to partial depletion of oxygen

The growth rate of Phycomyces blakesleeanus sporangiophores was found to be very sensitive to sudden changes in the oxygen concentration. A change from 20% to 15% oxygen elicits a transient decrease in the growth rate which returns to normal 10 min after altering the concentration. After a step change to 10% oxygen, the growth rate shows two minima at 6–8 and 30–35 min and it reaches about 80% of its original value 50 min after this change. A threshold curve for this negative growth response shows that sporangiophores begin to sense a decrease in the oxygen concentration from 20% to 17%. Seven phototropically abnormal mutants with defects in the genes madA to madG were tested for the oxygen response. Two strains, C149madD120 and C316madF48, were found to have recoveries different from those of the wild type after step changes from 20% to 10% oxygen.     

Negative phototropism in the piloboloid mutants of Phycomyces blakesleeanus Bgff.

The sporangiophore (spph) of a piloboloid mutant, genotype pil, of Phycomyces ceases elongation and expands radially in the growth zone shortly after reaching the developmental stage IV b. The pil spph is always negatively phototropic to unilateral visible light when its diameter exceeds 210 m. Photoinduction of spph initiation, light-growth response, threshold of light energy fluence rate for the negative phototropism, avoidance and gravitropism in the pil mutant are all normal. In liquid paraffin, the pil spph shows negative phototropism as does the wild-type spph. Genetic analyses indicate that the negative phototropism of the pil mutant is governed by the phenotypic characteristics of pil but not by specific gene(s) responsible for negative phototropism. These facts imply that the reverse phototropism of the pil mutant results from a loss of the convergent lens effect of the cell because of the increase in cell diameter.Abbreviations spph(s) sporangiophore(s) - wt(s) wild type(s)     

Effect of carbon source and pH of the growth medium on spore germination inPhycomyces blakesleeanus

Phycomyces blakesleeanus sporangiospores responded differently to activation by physical and chemical stimuli. Spores that were physically (heat shock) activated or chemically (ammonium acetate) activated germinated and grew at pH 4.5 with the hexoses glucose, fructose, galactose, andN-acetylglucosamine, and with glycerol and amino acids. Under these conditions, physically activated spores showed a lower, although significant growth with the hexoses fructose, galactose,N-acetylglucosamine and with glycerol. On the other hand, physically activated spores incubated at alkaline pH (pH 7.3) required glucose to germinate; a requirement not observed with chemically activated spores, which showed significant growth in the other hexoses tested. Both physically and chemically activated spores incubated at pH 7.3 were unable to germinate and grow with amino acids and glycerol. These results suggest that there are different targets for activation of the spores by physical and chemical treatments. The levels of the fermentative enzymes alcohol dehydrogenase and lactate dehydrogenase and of the oxidative enzyme NAD⁺-isocitrate dehydrogenase were higher in cells grown at pH 4.5 in medium containing glucose; however, alcohol dehydrogenase and lactate dehydrogenase appear not to be affected by a change in the pH of the growth medium.     

Interaction of light and temperature on seed germination of Rumex obtusifolius L.

Germination of Rumex obtusifolius L. seeds (nutlets) is low in darkness at 25° C. Germination is stimulated by exposure to 10 min red light (R) and also by a 10-min elevation of temperature to 35° C. A 10-min exposure to far-red light (FR) can reverse the effect of both R (indicating phytochrome control) and 35° C treatment. Fluence-response curves for this reversal of the effect of R and 35° C treatments are quantitatively identical. Treatment for 10 min with light of wavelenght 680, 700, 710 and 730 nm, after R and 35° C treatment, demonstrates that germination induced by 35° C treatment results from increased sensitivity to a pre-existing, active, far-red-absorbing form of phytochrome (Pfr) in the seeds.Abbreviations FR far-red light - P phytochrome - Pr red-absorbing form of P - Pfr far-red-absorbing form of P - R red light     

Analysis of growth and rotational behavior of sporangiophores in Pilobolus crystallinus (Wiggers) Tode

The growth and rotation of the sporangiophore of Pilobolus crystallinus, which are important factors in its phototropic behavior, were analyzed throughout its development. The sporangiophore initial emerged from the trophocyst and elongated at the extreme tip without rotating. The elongation rate of the sporangiophore apex then gradually decreased and the apex expanded radially to produce the sporangium, but no rotation occurred. A transient cessation of elongation after sporangium development was followed by resumption of both elongation and radial expansion in the region beneath the sporangium developing the subsporangial vesicle. Rotation was not obvious at this stage. Radial expansion of the subsporangial vesicle continued at a decreasing rate until full size was reached. Elongation then recommenced in the newly established growth zone in the upper region of the sporangiophore just beneath the subsporangial vesicle. During this period of growth, the sporangiophore rotated in a clockwise direction as viewed from above. All growth and rotation ceased about 1 h before ejection of the sporangium into the air. Based on these results, a modified classification of the developmental stages has been proposed.This work was carried out under the Joint Research Program of the Institute of Genetic Ecology, Tohoku University, Japan (892006). The authors please to thank Kaori Koga and Hiroko Kikuchi for their helpful assistance.     

A comparison of cell-wall-yielding properties for two developmental stages of Phycomyces sporangiophores

The yielding properties of the cell wall, irreversible wall extensibility (m) and yield threshold (Y), are determined for stage I sporangiophores of Phycomyces blakesleeanus from in-vivo creep experiments, and compared to the values of m and Y previously determined for stage IVb sporangiophores using the same pressureprobe method (Ortega et al., 1989, Biophys. J. 56, 465). In either stage the sporangiophore enlarges (grows) predominately in length, in a specific region termed the growing zone, but the growth rates of stage I (5–20 urn · min^–1) are smaller than those of stage IVb (30–70 m · min^–1). The results demonstrate that this difference in growth rate is the consequence of a smaller magnitude of m for stage I sporangiophores; the obtained values of P (turgor pressure), Y, and P-Y (effective turgor for irreversible wall extension) for stage I sporangiophores are slightly larger than those of stage IVb sporangiophores. Also, it is shown that the magnitude of m for the stage I sporangiophore is regulated by altering the length of the growing zone, L_g. A relationship between m and L_g is obtained which can account for the difference between values of m determined for stage I and stage IVb sporangiophores. Finally, it is shown that similar changes in the magnitude of m and (which have been used interchangeably in the literature as a measure of irreversible wall extensibility) may not always represent the same changes in the cell-wall properties.Abbreviations and Symbols L length - L_g length of growing zone - m irreversible wall extensibility - P turgor pressure - Y yield threshold - (P-Y) effective turgor for irreversible wall extension - relative irreversible wall extensibility - _g relative irreversible wall extensibility of the growing zone (m/L_g) This work was supported by National Science Foundation grant DCB-8801717 to J.K.E. Ortega.     

Interaction of light and temperature on the germination of Rumex obtusifolius L.

Seeds (nutlets) of Rumex obtusifolius L. fail to germinate in darkness at 25° C, but are stimulated by short exposure to red light (R) the effectiveness of which can be negated by a subsequent short exposure to far red light (F) indicating phytochrome control. Short periods of elevated temperature treatment (e.g. 5 min at 35° C) can induce complete germination in darkness. Although short F cannot revert the effect of 35° C treatment, cycling the phytochrome pool by exposure to short R before short F results in reversion of at least 50% of the population. Prolonged or intermittent F can also revert the germination induced by 35° C treatment. The effect of elevated temperature treatment is interpreted on the basis of two possible models; (i) that it increases the sensitivity of the seeds to a low level of pre-existing active form of phytochrome (Pfr) (ii) that it induces the appearance of Pfr in the dark. In both cases it is envisaged that elevated temperature treatment and Pfr control germination at a common point in the series of reactions that lead to germination.Abbreviations D Dark - F far red light - P phytochrome - Pr red absorbing form of P - Pfr far red absorbing form of P - R red light     

光温条件对狭翅大刀螳生长发育的影响及其捕食功能研究

室内条件下饲养狭翅大刀螳(Tenodera angustipennis),研究温度与光照两个因子对狭翅大刀螳生长发育的影响。同时考察狭翅大刀螳若虫对不同密度小菜蛾幼虫与成虫及萝卜蚜的捕食功能反应．结果表明。温度对狭翅大刀螳生长发育的影响显著,随着温度的升高。在设定的温度范围内其历期明显缩短．狭翅大刀螳1～3龄若虫最适生长温度为25℃。而4、5龄若虫的最适生长温度为25～30℃．单因子光照对狭翅大刀螳生长发育无显著影响．捕食功能反应试验所得的数据,按HoUing模型进行模拟,经卡方检验。其理论值与实测值无显著差异。证明建立的模型能较好地模拟狭翅大刀螳的捕食情况．     

Effects of temperature and light on cyst germination and germinated cell survival of the noxious raphidophyte Heterosigma akashiwo

The effects of temperature and light on the germination of Heterosigma akashiwo cysts were examined using bottom sediments collected from Hakata Bay, Japan. In a suspension of mixed sediment and seawater in the temperature range of 5–30 °C, motile cells emerged within 3 weeks, but at ≤12 °C the cell numbers were markedly lower and the emergence of motile cells delayed. When suspension samples incubated at various temperatures were moved to 20 °C and incubated, only a few additional motile cells emerged. The number of motile cells germinated in the dark was significantly lower than under light conditions. When suspension samples incubated in the dark were exposed to light, only a few additional motile cells emerged. These results indicate that the initiation of germination in Heterosigma cysts suspended in seawater is not dependent on temperature and light conditions, although the speed of the germination process is affected by temperature, and cell survival just after germination is strongly affected by temperature and light.     

Effect of temperature and light on the toxicity and growth of the blue-green alga Microcystis aeruginosa (UV-006)

The toxicity and growth of Microcystis aeruginosa (UV-006) from the Hartbeespoort Dam, South Africa were investigated at different temperatures and photon fluence rates under laboratory conditions. Cells harvested in late logarithmic growth phase were most toxic when grown at 20°C (LD₅₀) median lethal dose [IP, mouse]=25.4 mg kg^-1). Toxicity was markedly reduced at growth temperatures above 28° C. Fluence rate had a smaller effect on the toxicity of the cells, but toxicity tended to be less at the very low and high light fluences. Optimal conditions for growth did not coincide with those for toxin production. Well-aerated cultures of this isolate kept at pH 9.5 by CO₂ addition, a temperature of 20–24° C, a fluence rate of 145 mol photons m^-2 s^-1 and harvested in the late logarithmic growth phase yielded the maximum quantity of toxin.Abbreviation LD₅₀ median lethal dose An abstract of this work, presented as a poster at the IUBS symposium on toxins and lectins, held at the CSIR, Pretoria, South Africa during 1982 was published in S. Afr. J. Sci. 78, 375 (1982)     

Response of cylindrospermopsin production and release in Aphanizomenon flos-aquae (Cyanobacteria) to varying light and temperature conditions

The influence of light and temperature on the cylindrospermopsin (CYN) production of two Aphanizomenon flos-aquae strains, isolated from North-eastern German lakes, was investigated with semi-continuously growing cultures. A light gradient from 10 to 60 μE m⁻² s⁻¹ in combination with temperatures of 16, 20, and 25 °C was tested.CYN concentrations varied by a maximum factor of 2.7 in strain 10E9 with a significant decrease with increasing temperature. Strain 22D11 showed less pronounced changes, i.e. by a factor of 1.6, and without clear relationship to temperature.Reaction patterns of CYN production to changing light intensities are different at different temperatures. In both strains CYN concentrations increase significantly at 20 °C between 10 and 60 μE m⁻² s⁻¹, whereas they decrease significantly at 25 °C in the same light gradient. The amount of synthesised CYN is not reflected by growth rates of the strains in a uniform manner. Nonetheless several temperature–light combinations which constitute physiological stress seem to trigger CYN production and particularly CYN release from cells. The lowest growth rate observed at 16 °C and 60 μE m⁻² s⁻¹ of strain 22D11 may reflect photoinhibition due to the lower temperature and related limited CO₂-fixation. Under these conditions, extracellular CYN concentrations increased to 58% of total CYN, while the share of extracellular CYN of all other light and temperature regimes was 11–26%. From the results and the experimental design we conclude an active release of the toxin into medium to be more likely than mere leakage from cells.