Über einen intrazellulären Parasiten beiCryptomonas (Cryptophyceae), I

An intracellular parasite occurring inCryptomonas rostratiformis and less numerously also inC. erosa andC. phaseolus. The parasite is described. It grows in the dorsal side of the host near the nucleus from which it is optically indistinguishable in young stages. When mature the parasite fills 1/3 to 1/2 the volume of theCryptomonas cell. It is seen as a colourless blister, which pushes back the plastid of the host. Reproduction occurs by separation of the protoplast into a hundred or moreBodo-like swarmers which perhaps represent the infectious phase. Under certain conditions, however, such as during decline of theCryptomonas population, the parasite transforms into thick-walled spindle-shaped cysts. Like the swarmers these cysts are released by rupture of the cryptomonad cells. The fate of the cysts is not known. TheCryptomonas population is destroyed by the infection in the course of a few days. Literature studies have shown that the parasite has been known for a long time, but considered incorrectly by different authors as part of theCryptomonas, or as a result of phagotrophic uptake of theCryptomonas. The parasite is compared with a somewhat similar parasite inMallomonas, and with certain parasitic dinoflagellates. The similarity with the latter is superficial only as it posesses a eucaryotic nucleus. The parasite shows some similarity with the genusParadinium (Mycetozoa) as well as with certainSporozoa.

     

Phototactic responses of four marine dinoflagellates with different types of eyespot and chloroplast

Great structural variety is seen in the eyespot of dinoflagellates, a structure involved in phototaxis. Although there are several works on the phototactic responses in some species of dinoflagellates, none of the dinoflagellates used in these studies possessed an eyespot and, therefore, we have no knowledge of the relationship between eyespot type and phototactic response. In this study, we determined wavelength dependency curves for phototaxis in four marine dinoflagellates that possess a different type of either eyespot or chloroplast. These include: (i) a dinoflagellate possessing a peridinin-containing ohioroplast with an eyespot (Scrippsiella hexapraecingula Horiguchi et Chihara); (ii) a dinoflagellate containing a diatom endosymbiont and with the type B eyespot sensu Dodge (1984; (Peridinium foli-aceum (Stein) Biecheler); (iii) a dinoflagellate with peri-dinin-containing chloroplasts, but lacking an eyespot (Atexandrium hiranoi Kita et Fukuyo); and (iv) a dinoflagellate with fucoxanthin, 19′-hexanoyloxyfucoxanthin and 19′-butanoyloxyfucoxanthin, but lacking an eyespot (Gymnodinium mikimotoi Miyabe et Kominami ex Oda), Regardless of the eyespot or the chloroplast type, all four dinoflagellates showed similar wavelength dependency curves for phototaxis, with sensitivity between 380 and 520 nm, the highest peak at approximately 440 or 460 nm and smaller peaks or shoulders at 400–420 nm and 480–500 nm. Substantial peaks have also been noted in the ultraviolet range (260–280 nm). The ultrastructural study of the eye-spot of Scrippsiella hexapraecingula revealed that the eyespot consists of two layers of lipid globules and probably acts as a quarter-wave stack antenna.     

Phototaxis in Cryptomonas sp. under condition suppressing photosynthesis

Effects of 3-(3, 4-dichlorophenyl)-l, 1-dimethylurea (DCMU)on photosynthetic oxygen evolution, respiratory oxygen uptake,phototactic response and swimming rate in Cryptomonas sp. weredetermined and compared. Photosynthetic oxygen evolution wascompletely inhibited in the presence of 10^–5 M DCMU. Thetreatment did not significantly affect the rates of respiratoryoxygen uptake, phototaxis, and swimming, indicating that directparticipation of photosynthesis in the phototaxis of this algacan be ruled out. Wavelength dependency of photosynthetic oxygen evolution wasalso determined in the range of 560 to 700 nm. The rate of photosyntheticoxygen evolution at 680 nm was as high as that at 560 nm, butno phototactic activity was seen at 680 nm although it was maximumat 560 nm. This is consistent with the above conclusion. (Received February 16, 1976; )     

Diaphototaxis and gravitaxis in a freshwater Cryptomonas

Phototaxis and gravitaxis are characterized in a freshwater species of the flagellate Cryptomonas. The phototactic orientation in this limnetic species is unusual and differs from all other Cryptomonas species studied so far: At both low (< or = 1O W m-2) and higher fluence rates it orients perpendicular to the light beam (diaphototaxis) while another freshwater Cryptomonas species (strain CR-1) is restricted to positive phototaxis and the marine species, C. maculata, shows both a positive and a more pronounced negative phototaxis. The mechanism of light direction detection seems to depend on a periodic shading or irradiation mechanism as confirmed by the disturbance of phototaxis in the presence of high viscosity media. In addition, this freshwater species possesses a rather pronounced negative gravitaxis which is only partially modified by phototaxis. The ecological consequences of this behavior are discussed.     

Photoresponses of Chaoborus larvae

The diel vertical migration of Chaoborus larvae is a well known phenomenon. In order to quantify the ability of larvae to utilize underwater light cues in their migration, we measured photoresponses of fourth-instar Chaoborus punctipennis larvae in the laboratory. The action spectrum for these larvae was characterized by a maximum in sensitivity at 400 nm, a plateau at a lower sensitivity from 480 to 560 nm, and a region of much lower sensitivity at wavelengths longer than 620 nm. Dark-adapted larvae exhibited a positive phototaxis at low light intensity which shifted to a negative phototaxix as light intensity increased. At 540 nm the threshold intensity was 1.5 × 10^?9 W/m² for positive phototaxis and about 10^?6 W/m² for negative phototaxis. Light adaptation decreased sensitivity and altered the phototactic pattern. Larvae have a clear circadian rhythm in negative phototaxis, in which greatest responsiveness occurs early in the day. We suggest that the rhythm in photoresponsiveness primarily controls the timing of the downward migration at dawn.     

Loss of Phototaxis and Degeneration of an Eyespot in Long‐term Algal Cultures: Evidence from Ultrastructure and Behaviour in the Dinoflagellate Kryptoperidinium foliaceum

Phototaxis provides phytoplankton with the means to orient themselves in a light gradient. This is accomplished using an eyespot and associated organelles. For the dinoflagellate Kryptoperidinium foliaceum, which has been described as having one of the most elaborate eyespot complexes known, positive phototaxis has hitherto not been reported. In this study, we show that a newly isolated strain of K. foliaceum is indeed capable of positive phototaxis with a mean vector (± 95% confidence interval) of 352°± 2.2, where 0/360° indicates the position of the light source. A study of three strains (UTEX 1688, CCMP 1326, and MBL07) of K. foliaceum showed that the eyespot in two of these strains has degenerated following decades in culture. Thus, previous studies have failed to report positive phototaxis due to loss of directionality caused by the degenerated eyespot. The results are discussed in a broader context and we conclude that studies on algal morphology and physiology may result in erroneous conclusions if based on algal cultures maintained under laboratory conditions for extended periods.     

Action spectrum of phototaxis in a cryptomonad alga, Cryptomonas sp.

The action spectrum of the positive topo-phototaxis in Cryptomonaswas determined by photometry in the region of 400 to 680 nmat a stimulus intensity of 8.3 ? 10^–11 Einsteins cm^–2sec^–1. The action spectrum had a main peak at about 560nm unlike peaks for most other flagellated algae. Blue lightwas not very effective and red light above 640 nm had not effect. Swimming rates of individual organisms were measured by darkfield photomicrography. We concluded that the photokinetic effectwas negligible. Among the component pigments of this alga, phycoerythrin hadan absorption spectrum whose main peak appeared to coincidewith that of the phototactic action spectrum. (Received October 31, 1973; )     

CELL FORM AND SURFACE PATTERNS IN CHROOMONAS and CRYPTOMONAS CELLS (CRYPTOPHYTA) AS REVEALED BY SCANNING ELECTRON MICROSCOPY1

Fifteen freshwater cryptomonad species were freeze-dried and examined with the scanning electron microscope. Surveys of cell surfaces revealed four general cell types. Chroomonas type cells lack a furrow but possess a shallow vestibular depression where the flagella are inserted. The presence of a gullet could not be detected. Cryptomonas spp. displayed three morphological types, all lacking gullets. The first type of Cryptomonas has a simple, shallow furrow with ridges that apparently can close to form a raphe but an oval opening or stoma remains at the posterior end and an opening from the vestibulum is formed at the anterior end. The second Cryptomonas type consists of a complex furrow with furrow ridges and folds that extend almost two-thirds of the cell length. A sloma is present in the central region of the closed furrow. The folds apparently can separate thereby exposing the underlying furrow. The third type of Cryptomonas possesses a simple, non-closing furrow. At the anterior end there is a vestibular ligule which extends from the dorsalleft side of the cell and covers the region of the vestibulum where the contractile vacuole discharges.     

Multiple light inputs control phototaxis in Synechocystis sp. strain PCC6803

The phototactic behavior of individual cells of the cyanobacterium Synechocystis sp. strain PCC6803 was studied with a glass slide-based phototaxis assay. Data from fluence rate-response curves and action spectra suggested that there were at least two light input pathways regulating phototaxis. We observed that positive phototaxis in wild-type cells was a low fluence response, with peak spectral sensitivity at 645 and 704 nm. This red-light-induced phototaxis was inhibited or photoreversible by infrared light (760 nm). Previous work demonstrated that a taxD1 mutant (Cyanobase accession no. sll0041; also called pisJ1) lacked positive but maintained negative phototaxis. Therefore, the TaxD1 protein, which has domains that are similar to sequences found in both bacteriophytochrome and the methyl-accepting chemoreceptor protein, is likely to be the photoreceptor that mediates positive phototaxis. Wild-type cells exhibited negative phototaxis under high-intensity broad-spectrum light. This phenomenon is predominantly blue light responsive, with a maximum sensitivity at approximately 470 nm. A weakly negative phototactic response was also observed in the spectral region between 600 and 700 nm. A deltataxD1 mutant, which exhibits negative phototaxis even under low-fluence light, has a similar action maximum in the blue region of the spectrum, with minor peaks from green to infrared (500 to 740 nm). These results suggest that while positive phototaxis is controlled by the red light photoreceptor TaxD1, negative phototaxis in Synechocystis sp. strain PCC6803 is mediated by one or more (as yet) unidentified blue light photoreceptors.     

EFFECTS OF TEMPERATURE AND IRRADIANCE ON THE GROWTH OF TWO FRESHWATER PHOTOSYNTHET1C CRYPTOPHYTES1

Effects of light and temperature on growth of two freshwater photosynthetic cryptophytes of different cell size were studied in batch cultures. For the smaller Cryptomonas 979/67, Steele's model and equation of Platt et al. described the relationship between growth rate and photon flux density (PFD), whereas a hyperbolic tangent function gave a better fit for the larger Cryptomonas 979/62. Maximum growth rates given by the three models were consistent with each other, but the hyperbolic tangent function gave slightly lower estimates. Maximum growth rates in relation to temperature were well described for both species by the model of Logan et al. The optimum temperature for growth for Cryptomonas 979/67 was ca. 24.5° C and 19.0° C for Cryptomonas 979/62. The lethal temperatures were 30.4° C and 23.1° C for 979/67 and 979/62, respectively. The estimated maximum growth rates were 1.38 div.·day^?1 for Cryptomonas 979/67 and 0.87 div.·day ^?1 for Cryptomonas 979/62. There were interspecific differences in photoadaptation strategies, as Cryptomonas 979/67 required relatively high PFDs to show net growth, whereas Cryptomonas 979/62 grew at lower irradiances. Cryptomonas 979/67 showed photoinhibition soon after the saturation point, but Cryptomonas 979/62 tolerated a much wider range of irradiance. From their growth responses to light, Cryptomonas 979/ 67 appears to be a stenotopic and Cryptomonas 979/ 62 a eurytopic strain.     

Multiple pathways of excitation energy flow in the photosynthetic pigment system of a cryptophyte,Cryptomonas sp. (CR-1)*

Energy transfer pathways in a cryptophyte, Cryptomonas sp. (CR-1 strain) were investigated mainly by the steady state fluorescence spectroscopy and the time-resolved spectrum. Cryptomonas sp. (CR-1) contains chlorophyll (Chi) a, Chi c₂, carotenoids and cryptomonad phycoer-ythrin (Cr-PE₅₆₅), the last of which is known to be located in the lumenal side of the thyiakoid membranes. The spectral heterogeneity cf pigments was resolved by fluorescence spectra; there were at least five emission bands of Chi a at -196°C. Chlorophyll C₂ and carotenoids transferred independently to the common Chi a form (Chi a₆₆₃), and Cr-PE₅₆₅, to the different form (Chi a₆₈₂). Chlorophyll c₂ was not an intermediary component of energy transfer from carotenoid to Ch a; this is a common phenomenon to green algae and brown algae. The Chi a₆₆₃ and Chi a₆₈₂ are postulated to be located in the light-harvesting chlorophyll protein (LHC) II; thus, the energy is accumulated on Chi a₆₈₂‘n LHC II. The energy transfer step in Cr-PE_;565, was short, which was shown by a small, time-dependent red-shift of the emission. In the photosystem (PS) II core, two fluorescence components were resolved at 688 and 696 nm. The former was the trap at cryogenic temperatures. A large red-shift induced by the low temperature was explained by an equilibrium between Chi a₆₈₂ in LHC II and Chi a₆₈₈ in PS II core. The presence of Chi a₆₈₂ emission at physiological temperature is a unique feature of this alga. This was also reported in dinophyceae, which contain peridinin-ChI a-protein in the lumenal side of the thyiakoid membrane. Thus, this modification might be common in systems where the antenna complexes bind to the LHC II on the lumenal side. Based on the spectral data, we proposed a model for the molecular organization of PS II and the energy transfer pathways in cryptophyceae.     

Chlamydomonas reinhardtii Dangeard (Chlamydomonadales, Chlorophyceae) mutant with multiple eyespots

We have isolated a new Chlamydomonas reinhardtii Dangeard (Chlamydomonadales, Chlorophyceae) mutant with from one up to more than four eyespots cell^?1. It was designated mes (multiple eyespots)‐10 A wild‐type cell has a single eyespot, located under the chloroplast envelope, at a certain position near the cell's equator where the chloroplast envelope is in contact with the cell membrane. The eyespot(s) in mes‐10, however, are located at various positions on its chloroplast. The mes‐10 cells displayed negative phototaxis to 480–500 nm light. This behavior differed from that of a similar mutant, ptx4, which has been shown to have multiple eyespots and display no phototaxis (Pazour et al., J. Cell Biol. 1995; 131 : 427–40). Mes‐10 may retain a functional photoreceptor and a photosignal transduction system independently of its multiple eyespots. This mutant should be useful for studying how C. reinhardtii responds to light signals, as well as how eyespots are formed in the cell.     

Observations on the ultrastructure of the flagella and periplast in the Cryptophyceae

The flagella in Cryptomonas ovata Ehrenberg and two other un-named strains of Cryptomonas both bear stiff hairs with fine distal filaments of the same type as those found in the Xanthophyceae, the Chrysophyceae sensu stricto, the Phaeophyceae, the Bacillariophyceae, the Eustigmatophyceae and the Oomycetes. On the longer of the two flagella the hairs are 2·5 µm long and in two opposite rows whereas on the shorter flagellum they measure only 1 µm, are arranged in a single row and are more closely spaced. The long flagellum also bears a characteristic lateral swelling with a tuft of hairs of the same type as on the remainder of the flagellum, at approximately the level at which it emerges from the gullet. The hairs on the flagella of Hemiselmis rufescens Parke are distributed in a similar manner to those in Cryptomonas but they are more flexible and the swelling and tuft of hairs appear to be absent from the long flagellum. Hairs are apparently absent from the short flagellum of Chroomonas sp. The periplast in Cryptomonas ovata shows a hexagonal pattern in surface view and in sections of all three Cryptomonas strains appears as a typical plasmalemma underlain by a discontinuous layer of electron-dense material with variable substructure. The distribution of flagellar hairs and the structure of the periplast appear to be characters unique to the Cryptophyceae and these features emphasise the isolated position of this class of algae.     

Investigations on the phototactic orientation of Anabaena variabilis

Phototaxis of the blue-green alga Anabaena variabilis was studied using both population method and observation of single trichomes by microscope. The trichomes react positively at low and negatively at high illuminance. The inversion point lies at about 1000 1x. The action spectrum of positive phototaxis indicates that the photosynthetic pigments chlorophyll a, C-phycocyanin and allo-phycocyanin are involved in the absorption of the active light. The same range of wavelengths is active in negative phototaxis, but in addition, wavelengths between 500 and 560 nm and between 700 and 750 nm are also effective. Obviously pigments of unknown chemical nature are sharing in light absorption. Two alternatives are discussed. Since inhibitors of photosynthesis such as DCMU and DBMIB do not affect phototactic orientation, a direct coupling of phototaxis with photosynthesis can be excluded.Abbreviations DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - DBMIB Dibromothymoquinone (2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone) Presented in part at the International Symposium on Photosynthetic Prokaryotes: August 22–28, 1976, Dundee, Scotland     

Phototaxis in water fleas (Daphnia magna) is differently influenced by visible and UV light

The effects of vertical illumination with monochromatic lights on phototaxis of Daphnia magna in a test chamber were determined at five levels of equal quantal flux density (between 188 and 6.42 · 10⁻⁵ nEinstein). Visible adaptation light (500 nm) and subsequent spectral test light had the same quantal flux density. The animals reacted to ultraviolet light (260–380 nm) with negative phototaxis, whereas visible light (420–600 nm) caused positive phototaxis. Action spectra were determined, based on the evaluation of different parameters of phototactic behavior. The maximum spectral sensitivity in the ultraviolet was found at 340 nm. The maximum spectral efficiency in the visible varied in dependence on light intensity. Ecological consequences of the results are discussed. Accepted: 3 August 1998     

The eyespot of the flagellateTetraselmis cordiformis stein (Chlorophyceae): Structural spezialization of the outer chloroplast membrane and its possible significance in phototaxis of green algae

Summary The eyespot region of the flagellateTetraselmis cordiformis Stein (Chlorophyceae) was investigated with the freeze-fracture technique. The only fracture faces observed in this region were the two complementary fracture faces (PF and EF) of the outer chloroplast envelope membrane. Intramembranous particle numbers on both fracture faces of this membrane were significantly higher in the eyespot region as compared to regions outside the eye-spot. Higher numbers of particles on the PF face in the eyespot region were mainly caused by an increase in particle numbers of the size class 6–8 mm, while on the EF face particle size distribution was not significantly different between eyespot and other regions. Functional implications are discussed and evidence is presented that the outer chloroplast envelope membrane may be the site of photoreceptor location in green algal phototaxis.     

Diurnal vertical migration study during a winter bloom of Cryptophyceae in a floodplain pool

The diurnal vertical migration (DVM) of the phytoplankton community was studied in a small (270m²), shallow (1.8m), and frozen floodplain pool. Steep vertical gradients were detected in O₂, NH₄⁺-N, NO₃⁻-N and PO₄^3--P profiles. The phytoplankton of the pool is characterized by year round dominance of Cryptophyceae: Cryptomonas curvata and Cryptomonas marssonii created more than 90% of total phytoplankton biomass during the time of study. DVM was studied by analysing vertical profiles six times during a 24 hour cycle; samples were taken at 20 cm intervals along the profiles. Koliella planktonica, the only non-motile alga, showed a stable uniform distribution. Dinobryon divergens and Chrysococcus rufescens created a stable distinct concentration maximum at 40cm. Unlike these three species, both Cryptomonas spp. actively changed their position during the 24 hour cycle with distinctive evening downward and morning upward migration. The absence of filtering zooplankton excluded its influence on the patterns of phytoplankton DVM. The results showed the key role of PhAR (Photosynthetic active irradiance) in day - positioning of Cryptomonas. Night-time uptake of phosphate and/or ammonium at the bottom is probable, although direct evidence is lacking.     

Bi‐modal sensitivity to monochromatic light by the mud snail Ilyanassa obsoleta †

Under laboratory conditions the mud snail Ilyanassa obsoleta exhibits a pronounced positive behavioral response to monochromatic light. The response spectrum for‐this positive phototaxis has maxima at 480 nm and 560–580 nm. The threshold intensities for this response are 2.06 x 10^‐7 /μW/cm² for 480 nm and 2.18 × 10^‐7 μW/cm² for 580 nm. These results are suggestive of Ilyanassa's possessing two visual pigments with different absorption maxima.     

Changes in pigmentation of phytoplankton species during growth and stationary phase — consequences for reliability of pigment-based methods of biomass determination

In applied water ecology several methods for estimating the biomass or activity of phytoplankton depend on the proportion of accessory pigments (xanthophylls) to chlorophyll a. Therefore, changes in pigmentation during growth and stationary phase were investigated in four different species (Amphidinium klebsii, Euglena gracilis, Prymnesium parvum, Cryptomonas ovata) typical representatives of the major algal groups. The ratios of the different xanthophylls to chlorophyll a depended not only on the growth phase, but also on the species. InAmphidinium andEuglena, the ratio of xanthophylls to chlorophyll rises continuously during the growth phase and declined during the stationary phase. InPrymnesium, quantitative pigmentation was found to be nearly independent of the growth phase. InCryptomonas, however, this ratio was relatively constant during growth, but increased in the stationary phase. In contrast to higher plants, in which the breakdown of chlorophylls occurs before that of the xanthophylls, in three of the species both pigment classes were reduced in parallel when the cultures were in the stationary phase. AgingCryptomonas, however, exhibited a pigment breakdown pattern similar to higher plants. The use of these findings for the widely applied biomass determination by chlorophyll fluorescence and for other pigment-based methods is discussed.