PHYSIOLOGICAL RESPONSES DURING DARK SURVIVAL AND RECOVERY IN AUREOCOCCUS ANOPHAGEFFERENS (PELAGOPHYCEAE)1

The harmful bloom alga Aureococcus anophagefferens Hargraves et Sieburth can survive prolonged darkness, which could facilitate overwinter survival and dispersal by anthropogenic vectors such as ballast water. Experiments were conducted to examine the biochemical and photosynthetic changes in cells during dark storage. Cells were stored in the dark for periods from 2 to 14 days and were sampled at days 0, 1, 2, 4, 7, 10, and 14. Samples from days 2, 7, and 14 were monitored during a recovery period of 4–5 days. Physiological and photosynthetic parameters were measured during the dark storage and recovery periods. Cultures resumed growth quickly when returned to light, and bacterial counts remained constant during the dark storage period but increased rapidly during recovery periods. Cellular protein, carbohydrate, and lipid concentrations declined slightly during the dark period. There were no changes in chl a per cell or in RUBISCO per cell during 14 days of darkness. The data therefore suggest that A. anophagefferens is able to maintain its photosynthetic apparatus during dark storage periods of at least 2 weeks and relies on cellular reserves until it is returned to light to resume photosynthesis. During the recovery period in the light, the cells are able to acclimate rapidly to current light levels and resume growth.     

The "Point of no Return" Concept in Cell Division. The Effects of Some Metabolic Inhibitors on Synchronized Chlorella pyrenoidosa

The coarse of growth and cell division in synchronized cultures of Chlorella pyrenoidosa was studied after the addition of metabolic inhibitors at differing times during the cell cycle (14 h light - 10 h darkness with nitrate as nitrogen source. 12 h light: 12 h darkness with urea as nitrogen source). Dinitrophenol (DNP) added to a final concentration of 0.3 mM at any time in the synchronization cycle, the compound remaining in the suspension from the time of addition to the end of the dark period, inhibited spore formation completely. Growth measured as increase in cell volume was less sensitive to the action of the inhibitor. Chloramphenicol (CAP) added dining the 0–5 h interval to a final concentration of 0.1 mM resulted in 80 per cent inhibition of cell division. Similar treatment started at successive times thereafter resulted in a gradual decrease of the inhibition. Treatment at the 14th hour and during the dark period did not affect the sporulation. Similar experiments with 0.9 mM puromycin added at various times during the illumination period gave almost complete inhibition of cell division, while the growth was reduced by only 25 per cent. para-Fluorophenylalanine (p-FPhe) at 3.3 × 10^?2 mM stopped cell division nearly completely irrespective of addition time in the light period. Addition during the dark period also prevented an increase in the number of tree cells. In this case about half of the cells produced spores which were not released. It is concluded that DNP inhibits all stages of preparation for cell division, as well as the division process itself. With CAP a genuine transition point of preparation for cell division was observed, although its interpretation as related to protein synthesis is somewhat uncertain. With puromycin and p-FPhe no transitions were observed.     

A STUDY OF LIGHT INTENSITY,PERIODICITY, AND WAVELENGTH ON ZOOSPORE PRODUCTION BY PROTOSIPHON BOTRYOIDES KLEBS12

When mature Protosiphon cells were placed in darkness, zoospore production was more extensive and was completed in a shorter time at a temperature of 27 C than at 22 or 15 C. Cool-white fluorescent (Sylvania) light inhibited the process measurably at a radiation intensity of 0.6±10³ ergsjcm²-sec; inhibition was 96% complete at 14±10³ ergs/cm²-sec. For mature cells previously grown under repeated 12-12 hr light-dark cycles, a dark period of approximately 2 hr at 22 C allowed cell division to proceed to a stage such that reillumination did not inhibit continued development of zoospores. Monochromatic light from 402 to approximately -494 nm, as compared to darkness, inhibited zoospore formation; maximal inhibition was at 432-461 nm. In contrast, monochromatic light from 522 to 726 nm stimulated zoospore formation relative to darkness. Synchronous zoospore production was obtained using the following regimes: (A) 12 hr cool-white alternated with 12 hr yellow, (B) 12 hr cool-white alternated with 12 hr blue. Under regime A synchronous zoospore release (following synchronous production) occurred near the end of the yellow irradiation period, while under regime B it occurred near the end of the cool-white irradiation period. The significance of this in terms of photoprocesses and possible photoreceptors is discussed.     

Resting Stages of Skeletonema marinoi Assimilate Nitrogen From the Ambient Environment Under Dark,Anoxic Conditions

The planktonic marine diatom Skeletonema marinoi forms resting stages, which can survive for decades buried in aphotic, anoxic sediments and resume growth when re-exposed to light, oxygen, and nutrients. The mechanisms by which they maintain cell viability during dormancy are poorly known. Here, we investigated cell-specific nitrogen (N) and carbon (C) assimilation and survival rate in resting stages of three S. marinoi strains. Resting stages were incubated with stable isotopes of dissolved inorganic N (DIN), in the form of ¹⁵N-ammonium (NH₄⁺) or -nitrate (NO₃⁻) and dissolved inorganic C (DIC) as ¹³C-bicarbonate (HCO₃⁻) under dark and anoxic conditions for 2 months. Particulate C and N concentration remained close to the Redfield ratio (6.6) during the experiment, indicating viable diatoms. However, survival varied between <0.1% and 47.6% among the three different S. marinoi strains, and overall survival was higher when NO₃⁻ was available. One strain did not survive in the NH₄⁺ treatment. Using secondary ion mass spectrometry (SIMS), we quantified assimilation of labeled DIC and DIN from the ambient environment within the resting stages. Dark fixation of DIC was insignificant across all strains. Significant assimilation of ¹⁵N-NO₃⁻ and ¹⁵N-NH₄⁺ occurred in all S. marinoi strains at rates that would double the nitrogenous biomass over 77–380 years depending on strain and treatment. Hence, resting stages of S. marinoi assimilate N from the ambient environment at slow rates during darkness and anoxia. This activity may explain their well-documented long survival and swift resumption of vegetative growth after dormancy in dark and anoxic sediments.     

GROWTH OF TWO FACULTATIVELY HETEROTROPHIC MARINE CENTRIC DIATOMS1,2

The facultative, heterotrophs Cyclotella cryptica (sclone WT-1-8) and Coscinodiscus sp. were selectively isolated from coastal waters by dark incubation of organically enriched solid medium. C. cryptica grows in the dark with glucose and galactose, and Coscinodiscus sp. with glucose. Clone WT-1-8 of C. cryptica grows about twice as fast with glucose as a previously studied clone (0-3A). In the dark with, 5 × 10^?6 M glucose C. cryptica divides every 3 days, while with 5 × 10^?5 M glucose Coscinodiscus sp. divides every 10 days. Heterotrophic growth of either diatom for 1 year does not cause a major reduction in carbon, nitrogen, chlorophyll a, and chlorophyll c contents, or in photosynthetic ability, compared to light-grown cells. It is possible that facultative heterotrophy is of ecological benefit to these diatoms, probably for slow growth and survival during extended periods of dim light or darkness.     

HETEROSIGMA AKASHIWO (RAPHIDOPHYCEAE) RESTING CELL FORMATION IN BATCH CULTURE: STRAIN IDENTITY VERSUS PHYSIOLOGICAL RESPONSE 1,2

In this study, we examined the impact of environmental perturbation on the movement of the toxic bloom‐forming alga Heterosigma akashiwo (Hada) Hada ex Y. Hara et Chihara [syn. H. carterae (Hulburt) F.J.R. Taylor] between vegetative and resting cell phases of the life history. Resting state induction, in batch culture, was most effective when vegetative cells were subjected to low temperature (10° C) and darkness for extended time periods. Heterosigma cells in stasis had neither a cell wall nor scales but were surrounded by a calyx, most probably of polysaccharide composition. The resting cell was completely immobile, although both flagella remained attached. Heterosigma resting cells did not require a maturation period before successful activation to the vegetative state could occur. Cell division and motility were impacted sequentially during both the induction and activation phases of resting cell development. Our data show that Heterosigma had an obligate light requirement for resting cell activation. In replete medium, very low light fluences of 5 μmol photons·m ^{? 2}·s ^{? 1} were as effective as 60 μmol photons·m ^{? 2}·s ^{? 1} in the initiation of activation. Such sensitivity to extremely low light might give Heterosigma a competitive advantage for bloom formation in nature. Reduced nitrate levels significantly shortened the temporal transition of vegetative cells into the resting cell phase of the life history. Additionally, when resting cells induced in nitrate‐limited medium were activated under nitrate‐replete condition, the efficiency of the activation response was directly correlated to light availability. Both vegetative and resting cells maintained a haploid DNA complement. Rapid amplified polymorphic DNA (RAPD) analysis demonstrated variation in genetic identity among axenic Heterosigma strains. Strain identity influenced success in resting cell induction and survival in stasis. To date, no defined sexual cycle has been described. These observations are discussed in terms of population fitness. The data presented in this report provide a model algal system wherein the molecular events that govern long‐term stasis in an obligately autotrophic organism can now be assessed.     

Prolonged nitrate exhaustion and diatom mortality: a comparison of polar and temperate Thalassiosira species

The survival of two diatom species. Thalassiosira antarcticaComber isolated from the Southern Ocean and Thalassiosira rotulaMeunier isolated from the North Sea. was investigated duringa 21 day nitrate-exhaustion period, both in the light and indarkness. Both species endured 3 weeks of nitrate exhaustionin the light by forming a physiological resting state, characterizedby the development of shrunken, chlorotic protoplasts, a decreasein photosynthetic capacity and the accumulation of particulateorganic carbon (POC). These resting cells of both species stillresumed growth after 21 days of nitrate exhaustion, althoughthe viability of the cells decreased with time of nitrate exhaustion.Growth rates during subsequent growth experiments decreasedwith lengthening pre-incubation time in nitrate exhaustion.The viability of T.antarctica resting cells was lower than thatof T.rotula. After 21 days in nitrate exhaustion, T.antarcticagrew at 31% of the initial division rate, whereas the growthrate of T.rotula was 61%. When growth was resumed, accumulatedPOC decreased and paniculate organic nitrogen (PON), chlorophylla and photosynthetic carbon assimilation increased during thesubsequent 5 day growth periods, but never reached initial values.Darkness had no effect on cellular POC. PON and chlorophylla content of both species. In T.rotula, the capacity for photosyntheticcarbon assimilation decreased to almost zero during the 21 daydark period, although survival capacity was not affected. Aftera lag phase of 1–5 days, growth was resumed at initialgrowth rates, indicating that the bulk of cells of both diatomspecies were still viable. Thus, in the dark, both Thalassiosiraspecies survived nutrient exhaustion without physiological impairment.     

An extract of seeds fromAeginetia indica L., a parasitic plant,induces potent antigen-specific antitumor immunity in Meth A-bearing BALB/c mice

Summary The antitumor activity of an extract of seeds fromAeginetia indica L., a parasitic plant, was investigated. BALB/c mice, inoculated i.p. 1 × 10⁵ syngeneic Meth A tumor cells, were administered 2.5 mg/kgA. indica extract i.p. every 2 days from day 0. The untreated mice died of an ascitic form of tumor growth within 21 days, whereas all the treated mice completely recovered from tumor challenge without any side-effects. The extract did not exert direct cytotoxic activity against Meth A in vitro. Mice that survived after the first challenge as a result ofA. indica treatment overcame the rechallenge with homologous Meth A without additional administration of the extract. On the other hand, those mice could not survive after rechallenge with Meth 1 tumor cells, which were also established in BALB/c mice but were different in antigenicity from Meth A, suggesting the development of antigen-specific concomitant immunity in theA. indica-cured mice. In the induction phase of antitumor resistance in this system, CD4⁺ T cells appeared to be the main contributors, since in vivo administration of anti-CD4 mAb completely abolished such resistance. In contrast, anti-CD8 mAb administration did not influence the effect ofA. indica. The importance of CD4⁺ T cells in antitumor immunity was again clarified by Winn assay; that is, spleen and lymph node cells depleted of CD4⁺ T cells in vitro prior to assay abolished antitumor activity on co-grafted Meth A tumor cells in vivo.     

INCOMPLETENESS OF THE COCCOSPHERE AS A POSSIBLE STIMULUS FOR COCCOLITH FORMATION IN PLEUROCHRYSIS CARTERAE(PRYMNESIOPHYCEAE)1

Pleurochrysis carterae is a marine biflagellate that produces calcified structures called coccoliths. The coccoliths are formed inside the cells and released from the latter after formation. The light dependence of calcium incorporation in this species was studied using⁴⁵Ca as a tracer. Cells exposed to a repeating cycle of 16 h of light and 8 h of darkness incorporated calcium in extracellular coccoliths at a more or less constant rate throughout a cycle. The cells divided during the dark periods with a concomitant decrease in size. Their size increased during the light periods Coccolith formation in cells incubated in continuous darkness was greatly reduced and finally ceased. These cells did not divide and did not increase in size. Removal of extracellular coccoliths prior to the calcium incorporation experiments stimulated coccolith formation both in dark-incubated cells and in cells exposed to a repeating light-dark cycle. Cells in the stationary phase of growth ceased producing coccoliths. Calcification could be induced in these cells by removal of the extracellular coccoliths. Based on these findings we suggest that cells of Pleurochrysis carterae tend to produce a complete cover of coccoliths and that the available cell surface is a factor controlling coccolith formation.     

Discovery of a resting stage in the harmful,brown‐tide‐causing pelagophyte,Aureoumbra lagunensis: a mechanism potentially facilitating recurrent blooms and geographic expansion

To date, the life stages of pelagophytes have been poorly described. This study describes the ability of Aureoumbra lagunensis to enter a resting stage in response to environmental stressors including high temperature, nutrient depletion, and darkness as well as their ability to revert from resting cells back to vegetative cells after exposure to optimal light, temperature, and nutrient conditions. Resting cells became round in shape and larger in size, filled with red accumulation bodies, had smaller and fewer plastids, more vacuolar space, contained lower concentrations of chl a and RNA, displayed reduced photosynthetic efficiency, and lower respiration rates relative to vegetative cells. Analysis of vegetative and resting cells using Raman microspectrometry indicated resting cells were enriched in sterols within red accumulation bodies and were depleted in pigments relative to vegetative cells. Upon reverting to vegetative cells, cells increased their chl a content, photosynthetic efficiency, respiration rate, and growth rate and lost accumulation bodies as they became smaller. The time required for resting cells to resume vegetative growth was proportional to both the duration and temperature of dark storage, possibly due to higher metabolic demands on stored energy (sterols) reserves during longer period of storage and/or storage at higher temperature (20°C vs. 10°C). Resting cells kept in the dark at 10°C for 7 months readily reverted back to vegetative cells when transferred to optimal conditions. Thus, the ability of Aureoumbra to form a resting stage likely enables them to form annual blooms within subtropic ecosystems, resist temperature extremes, and may facilitate geographic expansion via anthropogenic transport.     

FACTORS AFFECTING DARK SURVIVAL OF THE BROWN TIDE ALGA AUREOCOCCUS ANOPHAGEFFERENS (PELAGOPHYCEAE)1

Aureococcus anophagefferens Hargraves et Sieburth is a pelagophyte responsible for the harmful brown tides in New York, New Jersey, and Rhode Island, USA. Recent reports of blooms in new areas, Maryland, USA, and Saldanha Bay, South Africa, suggest that the alga may be expanding its range, possibly through anthropogenic transport. Experiments tested the ability of A. anophagefferens to survive dark conditions, such as those that might be encountered during transport in ballast tanks or recreational boats. Laboratory cultures were stored in complete darkness for various lengths of time under different conditions. After returning cultures to optimal light and growth conditions, we recorded the time until growth resumed. Cultured A. anophagefferens was able to survive for at least 30 days in the dark. Temperature played a major role in dark survival, because cultures stored at 6° C and 12° C recovered faster than those stored at 18° C or 24° C. Growth phase at the time of storage had a minor effect on recovery, with exponential phase cultures resuming growth more quickly than stationary phase cells. Although the alga is known to have heterotrophic capabilities, the addition of low levels (1–3 μM) of organic nutrients did not appear to increase dark survival. Salinities within normal estuarine and oceanic ranges also did not affect survival. The ability of A. anophagefferens to survive dark periods could allow it to be transported by anthropogenic means to new regions, and temperature and length of storage appear to be key factors determining cell viability during prolonged darkness.     

Carbon-nitrogen relations during batch growth ofNannochloropsis oculata (Eustigmatophyceae) under alternating light and dark

Nannochloropsis oculata (strain CCAP 849/1) was sampled at least every 12 h over a 26-d period of batch culture growth in a 12 h/12 h light/dark illumination cycle. Exponential cell-specific growth rate was 0.5 d^–1. Cell division occurred during the dark phase, while ammonium uptake, pigment synthesis and cell volume increase occurred mainly during the light. Stationary phase cells were on average larger that the largest exponentially growing cells. The lag phase prior to cell division was short with the C/N ratio returning to 6.25 (from 28) within 2 d of refeeding with ammonium. Significant Chl.a synthesis commenced after this period; net synthesis of Chl.a ceased on exhaustion of the N-source with a 40% fall in levels by the end of the stationary phase. Levels of carotenoids per cell also declined during N-deprivation although per ml of culture levels remained constant. Ammonium-refeeding of N-deprived cells resulted in a very rapid rise in glutamine (Gln) and very high ratios of glutamine/glutamate (Gln/Glu peaking at 35 within 1 h); peak Gln/Glu was lower in cells refed in the dark or after a shorter period of N-deprivation. The major intracellular amino acids during exponential phase were Glu, Gln, alanine and arginine, but on exhaustion of the N-source, levels of Gln fell rapidly (Gln/Glu falling to below 0.1 from 0.5–0.9 in the light and 0.3 in darkness during exponential growth). During N-deprivation tyrosine accumulated within the cells. Comparisons are drawn with the growth ofIsochrysis galbana, another alga used in aquaculture, under identical conditions.Author for correspondence     

Hairy root culture of <Emphasis Type="Italic">Plumbago indica</Emphasis> as a potential source for plumbagin

Hairy roots of Plumbago indica were established at high frequency (90 %) by infecting leaf explants with Agrobacterium rhizogenes strain ATCC 15834. The axenic root cultures were established under darkness in hormone-free liquid Murashige and Skoog medium containing 3 % sucrose. The highest plumbagin content was found to accumulate in roots at their exponential phase of growth. A low pH (4.6) and a low concentration of sucrose (1 %) were beneficial for root growth in darkness, while pH 5.6 and 3 % sucrose under continuous irradiance enhanced plumbagin accumulation in roots up to 7.8 mg g⁻¹(d.m.). Direct shoot regeneration from hairy root culture was also achieved under continuous irradiance, thus indicated an easy way of obtaining transformed P. indica plants.     

Impact of light/dark regimen on growth rate,biomass formation and bacteriochlorophyll synthesis in Erythromicrobium hydrolyticum

The impact of illumination on specific growth rate, biomass formation, and synthesis of photopigment was studied in Erythromicrobium hydrolyticum, an obligately aerobic heterotrophic bacterium having the ability to synthesize bacteriochlorophyll a. In dark-grown continuous cultures the concentration of protein increased with increasing dilution rate, the concentration of bacteriochlorophyll a showed the opposite effect. At a dilution rate of 0.08 h^-1 (68% of _max in the dark) and S_R-acetate of 11.8 mM, the concentration of BChla of illuminated cultures in steady-state was 11–22 nM, compared to 230–241 nM in cultures incubated in darkness. No significant differences were observed in the concentration of protein. A shift from darkness to light conditions resulted in increased specific growth rates resulting in increased biomass formation, thus showing that light enhances growth by serving as an additional energy source. This phenomenon, however, was temporary because bacteriochlorophyll synthesis is inhibited by light. In contrast to incubation in continuous light or dark, incubation under light/dark regimen resulted in permanently enhanced biomass formation. In the dark periods, bacteriochlorophyll was synthesized at elevated rates (compared to constant darkness), thus compensating the inhibitory effect of light in the preceding period. It thus appears that the organism is well-adpated to life in environments with alternating light/dark conditions. The ecological relevance of the observations is discussed.Non-standard abbreviations BChla bacteriochlorophyll a - D dilution rate - spceific growth rate - K_s saturation constant - S_R concentration of limiting in inflowing medium of chemostat     

DIEL CHANGES IN PHASED-DIVIDING CULTURES OF CERATIUM FURCA (DINOPHYCEAE): NUCLEOTIDE TRIPHOSPHATES,ADENYLATE ENERGY CHARGE,CELL CARBON,AND PATTERNS OF VERTICAL MIGRATION1

The diel pattern of cell division, cell carbon, adenine nucleotides and vertical migration was determined for laboratory cultures of the photosynthetic marine dinoflagellate, Ceratium furca (Ehr.) Clap. & Lachm., entrained on an alternating 12:12 LD schedule at 20 C. Cell division was initiated during the latter portion of the dark period with ca. 30% of the population undergoing division. Cell C increased during the light period and exhibited a linear decrease with a loss of 33% during the dark period. ATP · cell^?1 increased during the light period and decreased by ca. 40–50% during the dark period. The diel patterns of cell C and ATP tended to “buffer” the magnitude of the change in C:ATP ratios around an overall mean value of 89. There was no obvious trend in the concentration of [GTP + UTP] · cell^?1 over the cell cycle. The cellular adenylate energy charge was maintained at values between 0.8 to 0.9 throughout the 24 h LD cycle, despite a ca. 40% decrease in total adenylates (A_T= ATP + ADP + AMP) during the dark period on 12:12 LD, and over a 68% decrease in ATP during 42 h of continuous darkness. These data lend experimental support to the theory of cellular metabolic control by the adenine nucleotides. With lateral illumination on 12:12 LD cycles, the cells began to concentrate at the surface of the experimental tubes shortly before the lights were turned on, and at the bottom of the tubes shortly before the lights were extinguished. This pattern continued for 6 days in continuous darkness, suggesting that the vertical migration pattern is independent of a phototactic response and may be under the control of an endogenous rhythm.     

Dark requirement for cell regeneration and colony formation by mesophyll protoplasts ofNicotiana plumbaginifolia Viv.

Summary The protoplasts ofNicotiana plumbaginifolia required darkness for cell regeneration and colony formation. Maximal plating efficiency of the protoplasts could be achieved by keeping the cultures in dark instead of light or dark/light sequence. Only two days of darkness prior to the illumination at 400 or 3,000 lux resulted in appreciable plating efficiency, than those of light from the beginning, but these values could not match the high plating efficiency in total darkness.     

FACTORS AFFECTING DORMANCY,GERMINATION, AND SEEDLING DEVELOPMENT OF AEGINETIA INDICA L. (OROBANCHACEAE)

Dormancy in seeds of the parasitic phanerogam Aeginetia indica L. can be broken by chemical treatment with sodium hypochlorite, which also helps to control contaminating microflora. A germination medium was developed that suppressed microbial contamination and permitted long-term observation of these slow-germinating seeds. The medium consisted of 10 ppm streptomycin, 10 ppm penicillin, and 10⁻⁵ m indole-3-acetic acid (IAA) (or other growth regulator) in 1 % water agar. Optimum germination range was 25–30 C. Dormancy could also be broken by exposure on agar for several days at 3-5 C (stratification), or by brief exposures (15 min) to 50 C. Continuous light as low as 0.1 ft-c completely inhibited germination on this growth medium. Brief, intermittent light exposures depressed germination. Germination and growth in vitro of nondormant seed of Aeginetina indica L. can be described in five stages: (1) Germination: expansion of spheroidal cells or nodule at micropylar end of the seed, stimulated by growth regulators. Unique stimulation of germination by IAA was noted; (2) Tendril formation: production of a root-hairlike protrusion in response to seedling roots or extract of pea seedlings; (3 and 4) Tendril septation and branching: induced by pea extract; (5) Seedling extension growth: cell growth and division adjacent to nodule by action of various carbohydrate-containing growth factors. This type of growth may bypass tendril formation.     

Tolerance for Prolonged Darkness of Three Phytoplankton Species, Microcystis aeruginosa (Cyanophyceae), Scenedesmus quadricauda (Chlorophyceae), and Melosira ambigua (Bacillariophyceae)

Phytoplankton community dynamics are affected not only by atural events such as overwintering but also by artificial events such as artificial circulation and related darkness conditions. In order to clarify the effect of tolerance for prolonged darkness on community succession, laboratory cultures of three phytoplankton taxa, Microcystis aeruginosa(Cyanophyceae), Scenedesmus quadricauda(Chlorophyceae), and Melosira ambigua(Bacillariophyceae) were carried out in darkness. The period of darkness was varied: 5, 10, 15, 20 days, and the control. Thereafter, all samples were reilluminated. After more than 10 days of darkness, M. aeruginosa decreased markedly with the length of the darkness period and was reduced to only 1% of the initial cell number after 20 days darkness. In contrast, S. quadricauda and M. ambigua retained their biomass even after 20 days of darkness. After restarting the light–dark cycle, however, all three species similarly increased exponentially and reached their maximum biomass levels. These results suggest that differences in tolerance for prolonged darkness may cause the succession of the phytoplankton under certain conditions.     

Dibutyryl c-AMP as an inducer of sporidia formation: Biochemical and antigenic changes during morphological differentiation of Karnal bunt (<Emphasis Type="Italic">Tilletia indica</Emphasis>) pathogen in axenic culture

Effect of dibutyryl adenosine 3′,5′-cyclic monophosphate (dbc-AMP), an analogue of c-AMP, was investigated on growth and morphological differentiation ofTilletia indica. Exponential growth was observed up to 21 days in both presence and absence of dbc-AMP; however, increasing concentration of dbc-AMP was deleterious to mycelial growth in liquid culture. A slow increase of mycelial biomass up to 21 days and decline at 30 days in the presence of 2.5 mM dbc-AMP was observed, therefore, this concentration was chosen in subsequent investigations. The inhibitory influence of dbc-AMP was further substantiated by decrease in soluble protein. The fungus on exposure to dbc-AMP experienced morphological differentiation from vegetative mycelial phase to sporogenous mycelial phase, and was induced to produce filiform sporidia. Use of quantitative ELISA further suggested that sporidia formation took more than 21 days in the presence of dbc-AMP. Variations of proteins during different stages ofT. indica grown in the presence and absence of dbc-AMP suggested the expression of stage-specific proteins or differential expression of proteins induced by dbc-AMP. The changes in expression of cell surface antigens as evidenced from decrease and increase binding of anti-mycelial and anti-sporidial antibodies in dbc-AMP treated culture by ELISA was further interpreted on the basis of morphological differentiation from mycelial to sporidial phase     

HCO3− and CO2 leakage from Synechococcus UTEX 625

The leakage of various inorganic carbon species from air-grown cells of Synechococcus UTEX 625 was investigated after a light to dark transition or during a light period using a mass spectrometer under a wide variety of experimental conditions. Total inorganic carbon efflux and CO₂ efflux during the initial period of darkness were measured with or without carbonic anhydrase in the reaction medium respectively. The HCO₃^? efflux after a light to dark transition was estimated by difference. Carbon dioxide efflux in the light was measured by inhibiting CO₂ transport with either Na₂S or COS₃ or quenching the ¹³C inorganic carbon transport by the addition of ¹²C inorganic carbon in excess. In cells in which CO₂ fixation was inhibited, when only the HCO₃^? transport system was fully operative, CO₂ effluxed continuously during the light period at a rate equal to about 25% of that in darkness. When only the CO₂ transport system was operative, HCO₃^? effluxed during the light period. The difference between the light and dark efflux rates was consistent with a 0.6 unit decrease in the intracellular pH upon darkening the cells. The permeabilities of the cell for CO₂ (2.94 ± 0.14 ± 10^?8ms^?1; mean ± SE, n=137) and HCO₃^? (1.4–1.7 ± 10^?9 ms^?1) were calculated.