INFLUENCE OF ULTRAVIOLET RADIATION ON GROWTH AND PHOTOSYNTHESIS OF TWO COLD OCEAN DIATOMS1

The influence of chronic exposure to UV-B and UV-A radiation on growth and photosynthesis of two polar marine diatoms (Pseudonitzschia seriata and Nitzschia sp.) was investigated in cultures exposed to moderate photon fluences for 3–7 days. Population growth rates were diminished 50% by UV-B. Fluorescence induction kinetics of photo-system II (PSII) revealed that UV-B caused lower F_v/F_m ratios and half-rise times, indicating damage to the reaction center of PSII and to related elements of the photosynthetic electron transport chain. Carbon assimilation rates per cell and per chlorophyll a were nonetheless highest for UV-B—exposed populations, which also had the highest chlorophyll a content per cell. The UV-B—exposed cells were, however, more vulnerable to visible light-induced photoinhibition. Exposure to UV-A in the absence of UV-B had little effect on growth, fluorescence induction of PSII, or chlorophyll a contents but did have some inhibitory effects on carbon assimilation per chlorophyll a and per cell. The increased photosynthetic capacity of UV-B-exposed cells suggested some ability to compensate for damage to the photosynthetic apparatus.     

THE ACCLIMATED RESPONSE OF GROWTH,PHOTOSYNTHESIS, COMPOSITION,AND CARBON BALANCE TO TEMPERATURE IN THE PSYCHROPHILIC ICE DIATOM NITZSCHIA SERIATA1

Nitzschia seriata Cleve, a common member of marine bottom ice communities in the Arctic, was grown in unialgal batch cultures to test for compensatory mechanisms for the low temperatures (?1.8° C) typical of its natural habitat. The upper lethal limit for growth was between 12° and 15°C, and the optimum was between 6° and 12° C. The Arrhenius function adequately (R²= 73%) fitted the relationship between growth rate and temperature from – 1.6° up to 10° C, with an average Q₁₀ of 1.9 over the entire range. Light-saturated and light-limited rates of photosynthesis (normalized to chlorophyll a or cell carbon) showed complete compensation from 12° to 4° C. Photosynthetic rates, especially at light saturation, declined rapidly at temperatures below 4° C. Susceptibility to photoinhibition was greatest at the lowest growth temperatures. Cellular composition (chlorophyll a, protein, polysaccharide, and lipid contents) was not systematically related to temperature in any simple way, although cell size (carbon per cell) was maximal at the lowest growth temperature. Dark respiration was unmeasurably low (<0.015 day^?1) at all growth temperatures. The strategy of adaptation in N. seriata may be characterized as optimizing efficiency and compensation, rather than maximization, of growth rate.     

Production potential of eicosapentaenoic acid by the diatom Nitzschia laevis

To investigate the production potential of eicosapentaenoic acid (EPA) by the diatom Nitzschia laevis, the growth characteristics and fatty acid composition of the cells were studied under photoautotrophic, mixotrophic and heterotrophic conditions of growth. The specific growth rate and maximum biomass concentration were respectively 0.466 d^–1 and 2.27 g l^–1 for mixotrophic culture, 0.344 d^–1 and 2.04 g l^–1 for heterotrophic culture, and 0.167 d^–1 and 0.5 g l^–1 for photoautotrophic culture, respectively. As for EPA production, the yield and productivity were respectively 52.32 mg l^–1 and 10.46 mg l^–1 d for mixotrophic culture, 35.08 mg l^–1 and 6.37 mg l^–1 d for heterotrophic culture, and 6.78 mg l^–1 and 3.39 mg l^–1 d for photoautotrophic culture, respectively. Results suggest that mixotrophic culture is the most suitable growth mode for the production of EPA by the diatom Nitzschia laevis. The results are useful for the development of a cost-effective fermentation process for EPA production by Nitzschia laevis.     

ENDOBACTERIA IN THE DIATOM PINNULARIA (BACILLARIOPHYCEAE). II. HOST CELL CYCLE‐DEPENDENT TRANSLOCATION AND TRANSIENT CHLOROPLAST SCARS1

Rod‐shaped bacteria were found together with the “secondary chloroplast” in the endoplasmic reticulum (ER) in the pennate diatom Pinnularia. During the host interphase, bacteria bore cavities into the chloroplast and interacted with thylakoids, forming a functional unit with the plastid of the engulfed and reduced eukaryotic endocytobiont, without perforating the relict cell membrane and the chloroplast envelope. Fluorescently labeled antibodies directed against the large subunit of RUBISCO elicited the same pattern as DAPI–DNA complexes. In pre‐prophase, bacteria started to dissociate from the plastids and left scars at their previous locations. In profile, scars appeared as granular amorphous regions interrupting several stacks of thylakoids, whereas images of glancing sections showed foci of circumscribed spiral domains. The vortex pattern was interpreted as the result of a screwing movement of the bacteria during their withdrawal, initiated while structurally still connected to the thylakoids. Scars became effaced, and thylakoids reoriented during prophasic translocation of the complex plastid from the girdle to the valve. In the transition to prophase, bacteria were found as clusters inside ER cisternae near the nucleus, where the microtubule‐organizing center was accompanied by the spindle precursor. Microtubules were seen to be aligned with ER profiles (containing bacteria). TEM images indicated that intracellular long‐distance transport is controlled by the host cytoskeleton acting upon the ER. Restricted to this stage, bacteria appeared to divide and occasionally bore tentacle‐like appendages. Their intraluminal localization at the nucleus in prophase, near the new plasmalemma after cleavage, and their return to the chloroplasts shortly afterward revealed a cell cycle‐dependent translocation with the ER as circulatory system and, together with the obvious retardation of their division cycle, a domestication by the host.     

我国首次记录的菱形藻属植物

利用透射电镜(TEM)研究我国南海近岸水中的微型硅藻时,发现了菱形藻属Nitzschia Hassall在我国首次记录的5个种,它们是：趋光菱形藻N．agnita Hustedt,金色菱形藻N．aurariae Cholnoky,沟坑菱形藻N．lacuum H．Lange-Bertalot,极细菱形藻N．perspicua Cholnoky和绒毛菱形藻N．pubens Cholnoky     

COMMUNITY STRUCTURE DYNAMICS OF EPILITHIC AND EPIPHYTIC DIATOMS IN A MISSISSIPPI STREAM1

Epilithic and epiphytic diatoms were collected monthly from 18 June 1979 through 19 May 1980 from both shaded and unshaded sites of Sessums Creek, a shallow, oligotrophic and strongly alkaline stream in northeastern Mississippi. The dominant macroalgae were filamentous green algae belonging to the non-mucilage producing genera Cladophora and Rhizoclonium. Ninety taxa were identified with Navicula minima Grun. and Nitzschia dissipata (Kütz.) Grun. accounting for 50% of all valves counted. Other important taxa were Navicula menisculus var. upsaliensis (Grun.) Grun., N. cryptocephala var. veneta (Kütz.) Rabh., Achnanthes minutissima Kütz. and Cymbella turgida (Greg.) Cl. With few exceptions, the more dominant taxa were equally abundant in the shaded and unshaded sites and also in the epilithon and epiphyton. Species diversity (H') and the number of taxa in a sample in all four habitats showed an identical pattern, being lowest in winter and highest in fall. No one pair of habitats was more structurally similar than any-other pair when compared by a similarity index (SIMI). Apparently, differences in light intensity and substrate type had little effect on diatom distribution in Sessums Creek and it was concluded that the locality sampled supported a single, nearly homogeneous diatom community.     

Determination of biomass dry weight of marine microalgae

Total biomass dry weight (DW) and ash free dry weight (AFDW) of five species of marine microalgae, Dunaliella sp., Isochrysis galbana, Nannochloropsis sp., Nitzschiaclosterium and Porphyridium cruentum, retained on filter paper, were determined. Dunaliella and Isochrysis cells have no cell wall; Nannochloropsis, Nitzschia and Porphyridium possess a cell wall and Nitzschia and Porphyridium cells are covered by silica and mucilage coating, respectively. In all these algae, DW of non-washed samples was at least 1.2 times higher than those washed by distilled water,0.9% sodium chloride, 0.5 M ammonium formate or 0.5 M ammonium bicarbonate. DW of 0.9% sodium chloride washed samples was more than 0.8 times higher than the other three washed samples. In most of the cases, there was no significant difference between DW of samples washed by ammonium formate and ammonium bicarbonate solutions (p>0.05). The AFDW of the non-washed algal samples was about twice that washed samples, and could be accounted for by volatile component in the sea water medium. Isotonic solution of ammonium bicarbonate is a satisfactory washing agent for algal cells for dry weight determination. This revised version was published online in September 2006 with corrections to the Cover Date.     

Relationships between phytoplankton and periphyton communities in a central Iowa stream

Relationships between phytoplankton and periphyton communities were investigated in a central Iowa stream. Results generally support the hypothesis that the phytoplankton community arises from the epipelic periphyton community. A high correlation existed between the proportion of benthic diatoms composing the epipelon and phytoplankton. One dominant epipelic species (Nitzschia acicularis) showed a greater tendency to become planktonic than the grouped remainder of Nitzschia spp. There was a significant inverse relationship between the proportion of centric diatoms in the plankton and volume of flow. Centric diatoms were important members of the plankton only when volume of flow was less than 60 ft³ / sec (2.1 m³ / sec). Possible mechanisms explaining these phenomena are discussed.This study represents a portion of a dissertation submitted to the Graduate College, Iowa State University in partial fulfillment of requirements for the degree Doctor of Philosophy.     

Diatom mineralization of silicic acid

Silicic acid binding, possibly at a membrane site is suggested as the first step in Si(OH)₄ metabolism in the marine diatom Nitzschia angularis. We estimate 1738±133 Si(OH)₄ binding sites·m^-2 cell surface and a turnover of 4–12 Si(OH)₄ molecules·s^-1 at maximum transport velocity. All studies were carried out using ⁶⁸Ge(OH)₄ as a tracer for Si(OH)₄.After Si(OH)₄ uptake, rapid (<1 min) transformation or intracellular binding was demonstrated; yet the extractable pool size after 1 min was indicative of transport against a concentration gradient. Initial uptake kinetics were linear for 150 s and saturation kinetics were demonstrated with kinetic parameters of 560 pmol Si(OH)₄·10⁶ cells^-1·min^-1 (V _max) 4.2 mol Si(OH)₄·L^-1(K_s). A metabolic energy requirement for transport was suggested by inhibition of uptake by agents that uncouple or inhibit phosphorylation; transport also was sensitive to agents that block sulfhydryl groups. Such characteristics are consistent with Si(OH)₄ transport being an active carrier mediated process.Rates of Si(OH)₄ transport were regulated during various growth stages and during the synchronized cell cycle. In Si(OH)₄ starved cells, blocked at the initiation of silica frustule formation, cycloheximide treatment caused a rapid decline of transport rate. Blocked cells, placed in the dark, maintained high transport rates for 6 h after which there was a loss of activity during the following 18 h. Light dependent recovery of transport ability in 12 h predarkened cells was dependent on de novo protein synthesis.Abbreviations ASW artificial sea water - CCCP carbonyl cyanide-m-chlorophenyl hydrazone - DCMU 3(3,4-dichlorophenyl-1,1-dimethyl urea) - 2,4-DNP 2,4-dinitrophenol - ESWT enriched sea water with tryptone - NEM n-ethylmaleimide - pCMB p-chloromercuribenzoic acid     

AN OUTBREAK OF DOMOIC ACID POISONING ATTRIBUTED TO THE PENNATE DIATOM PSEUDONITZSCHIA AUSTRALIS1

A bloom of the pennate diatom Pseudonitzschia australis Frenguelli (= Nitzschia pseudoseriata Hasle) occurring in Monterey Bay, California, in early September 1991 coincided with an episode of mortality in brown pelicans (Pelicanus occidentalis) and Brandt's cormorants (Phalacrocorax penicillatus). High levels of domoic acid (DA), the amnesic shellfish poisoning toxin, were recorded in the plankton samples. Furthermore, high levels of DA, as well as numerous remnants of P. australis frustules, were found in the stomach contents of affected birds and in the visceral contents of local anchovies, a principal food source of seabirds. This is the first confirmed report of DA poisoning since the original 1987 episode in Atlantic Canada caused by Nitzschia pungens Grunow forma multiseries Hasle. It suggests another species of planktonic pennate diatom is capable of producing DA and that herbivorous finfish can act as vectors for this toxin.