ULTRASTRUCTURE OF THE GAMETE OF PEDIASTRUM DUPLEX (CHLOROPHYCEAE)1

Gametes of Pediastrum duplex Meyen were investigated ultrastructurally, with emphasis on the flagellar apparatus. The cells are naked, biflagellate, and measure approximately 2.5 × 8 μm. Distinguishing them from zoospores is their possession of an eyespot and mating structure (the apical cap), and their lack of the peripheral band of cytoplasmic microtubules involved in colony formation. Four featurs of the flagellar apparatus are especially noteworthy: (1) the basal bodies are directly opposed and (2) are interconnected via their cores, (3) the central portion of the distal fiber is elaborated into an unusual ribbed structure which overlies the striated microtubule-associated component (SMAC) of the two-membered rootlets, and (4) the X-rootlets are dissimilar in microtubular number. The smaller X-rootlet consists of four microtubules in a three over one (3/1) configuration, whereas the larger has been found to be either 5 / 1, 6 / 1 or 7 / 1. The former rootlet extends past the nucleus whereas the latter extends down the opposite side of the cell, passing near the eyespot. The first two of these flagellar apparatus features have been previously noted in other motile cells of the Hydrodictyaceae. Although not specifically mentioned, published micrographs suggest the presence of the latter two as well, which may indicate that all four flagellar apparatus features are characteristics of all motile cells in the Hydrodictyaceae.     

STRUCTURE AND FUNCTION OF THE BRISTLES OF PEDIASTRUM BORYANUM (CHLOROPHYTA)1

Tufts of long delicate bristles were detected on mature colonies of Pediastrum boryanum (Turp.) Meneghini. The bristles are not uniform in length and can exceed 100 μm. Bristle number per tuft can exceed eighty. Ultrastructure studies revealed that tufts are an aggregate of hexagonal tubules arranged in staggered rows. Each hexagonal tubule has an inner diameter of 6 nm and is made up of six interconnected subunits 4 nm in diameter that are shared by adjoining tubules. The bristles can be easily removed from mature colonies with a vortex stirrer. Removal of bristles from mature colonies in culture results in the loss of buoyancy and subsequent settling to the bottom of the flask.     

PHOTOSYNTHETIC CAPACITY AND LUXURY UPTAKE OF CARBON DURING PHOSPHATE LIMITATION IN PEDIASTRUM DUPLEX (CHLOROPHYCEAE)1

When cells of Pediastrum duplex Meyen experience phosphorus depletion, their capacity for carbon fixation declines, but sizes and carbon contents of the cells increase several-fold, an apparent instance of “luxury uptake” of carbon. Maximum rates of uptake of phosphate increase during the same period, and are consequently correlated with the enlarged surface area of the cells. Thus the disadvantage of increased cell volume, which may accelerate sinking speed in nature, is offset by the increased capacity of the cells for nutrient uptake.     

A RHIZOPLAST IN CARTERIA RADIOSA (CHLOROPHYCEAE)12

A rhizoplast or rhizoplast-like structure was observed with the electron microscope in Carteria radiosa. The cross-banded structure extends from the proximal end of each of at least 2 of the basal bodies and extends toward, although does not make contact with, the nucleus. The rhizoplast terminates in a ribosome-free area composed of fine granules and microfibrils. This is the first ultrastructural verification of a rhizoplast in a volvocalean alga.     

SECONDARY CAROTENOID ACCUMULATION IN SCENEDESMUS KOMAREKII (CHLOROPHYCEAE, CHLOROPHYTA)

As Scenedesmus komarekii Hegewald was cultured under high light intensity and nitrogen limitation, the color of cells progressed from green to brown, and finally through orange to brick red. The secondary carotenoids astaxanthin and canthaxanthin, as well as apolar carotenoids, were detected in the brown and orange cells. These carotenoids were contained in lipoidal globules that were first formed at the periphery of the cell and progressively propagated toward its inside, eventually filling most of it. The chloroplast was single and parietal in the green cells. As the cells turned brown, the chloroplast divided into several small lobes and was pushed toward the interior by the accumulating lipoidal globules. Sometimes the outer layer of the wall of the brown cell developed one or two diametrically opposed swellings. Once the cells became orange or red, neither lipoidal globules nor any major organelles were distinguishable. The cell wall in the orange cells became thick because of the formation of electron-dense granules between its outer and inner layers. The mode of the secondary carotenoid accumulation in S. komarekii differs from that of Haematococcus, an alga well known for its ability to accumulate secondary carotenoids, but resembles that of " Chlorella " zofingiensis (= Mychonastes zofingiensis (Dönz) Kalina et Punčochářová).     

MITOSIS AND CYTOKINESIS IN SESSILE SPORANGIUM OF TRENTEPOHLIA AUREA (CHLOROPHYCEAE)1

An ultrastructure study of mitosis and cytokinesis in the sessile sporangium of Trentepohlia aurea (L.) Mart, was made to clarify the phylogenetic position of the alga. Mitosis was closed and centric at late anphase with cytokinesis involving the production of cleavage membranes by dictyasames between the numerous, well-separated daughter nuclei. Neither phycoplast nor phragmoplast microtubules were observed during cytokinesis. The lack of phycoplast microtubules and the presence of multilayered structures in flagellated cells suggest Trentepohlia is phylogenetically related to those green algae thought to have given rise to the land plants. The primitive type of mitosis and the lack of microbodies suggest that the ancestors of Trentepohlia may have branched off from this line relatively early.     

PHOTOSYNTHESIS IN THE SNOW: THE ALGA CHLAMYDOMONAS NIVALIS (CHLOROPHYCEAE)1

Red blooms of snow algae consisting almost exclusively of large spherical red cells of Chlamydomonas nivalis (Bauer) Wille are widespread during the summer in the Beartooth Mountains in Montana and Wyoming. Field studies designed to examine the effects of temperature, light, and water potential on algal activity were performed with natural populations using photosynthetic ¹⁴C-HCO₃- or ¹⁴CO₂ incorporation as a measure of activity. The algae photo-synthesized optimally at 5.4 × 10⁴ lx, but were not inhibited by increased light intensity up to 8.6 × 10⁴ lx, the maximum observed in the field. Photosynthesis was sensitive to a reduction in water potential, and since low water potentials develop in snow at temperatures below 0 C, it is unlikely that significant algal activity occurs at the sub-0 temperatures which occur throughout winter. Photosynthesis was much lower following melting of the snow, but this was probably due to decreased diffusion of CO₂. The optimal temperatures varied considerably among the different algal populations. Most samples photo-synthesized optimally at 10 or 20 C but retained substantial activity at temperatures as low as 0 or -3 C. Exceptional samples photosynthesized optimally at 0 or -3 C. It is proposed that the varied temperature responses reflect the presence of different temperature strains. Taken together, the data suggest that development of the snow algae can occur only during the summer months.     

PRODUCTS OF PHOTOSYNTHESIS IN CAULERPA SIMPLICIUSCULA (CHLOROPHYCEAE)1

The kinetics of carbon flow through various metabolites of Caulerpa simpliciuscula C. Ag., a siphonaceous green alga, are described. The pattern of C fixation in this alga differs from those observed in higher plants and other green algae in a number of respects. After 40 min incubation, soluble β-linked polyglucans are the most important labelled carbohydrates. Sucrose, although delectable, is never a major recipient of label and does not label until after other oligosaccharide fractions. The sugar monophosphates contain a large proportion of the ¹⁴C assimilated even after 40 min and behave not only as metabolic intermediates, but also as storage pools. The pattern of ammo acid labelling resembles that reported for other species of green algae in that alanine becomes labelled most rapidly, followed by glycine, and much later by glutamate, glutamine and asparagine. These labelling patterns are discussed in the light, of what is known of patterns of C flow in other algae.     

MORPHOGENESIS OF MONOSTROMA OXYSPERMUM (KÜTZ.) DOTY (CHLOROPHYCEAE) IN AXENIC CULTURE,ESPECIALLY IN BIALGAL CULTURE1

The typical morphology of Monostroma oxyspermum (Kütz.) Doty is lost in axenic culture. In synthetic media of the ASP type, it grows as a colony-like mass composed of round cells with numerous rhizoids. Such a mass is a fragile structure which falls apart upon shaking, or slight touch, into small cell-groups and single cells or cells with a long rhizoid. Only temporary saccate or monostromatic fronds appear and reach 1–2 mm in length when grown in enriched seawater media, but disintegrate and become a colony-like mass. The typical morphology is easily restored by adding at specific intervals filtrates of bacterial cultures and supernatant medium from axenic brown and red algal cultures to the basal medium (ASP7), or by reinfecting the Monostroma with an appropriate bacterial flora. Furthermore, the typical morphology in also maintained by bialgal cultures between Monostroma and other axenic strains of various species of seaweeds except the species belonging to the Chlorophyceae. Monostroma thus appears to utilize some substances released by most species of brown and red algae for its typical growth. Active substances released by bacteria, brown and red algae have not yet been identified and purified. However, it is demonstrated that in axenic cultures many species of seaweeds produce active extracellular substances which play an important role in growth and Morphogenesis of other species of seaweeds.     

ROLE OF PROLINE ACCUMULATION IN RESPONSE TO TOXIC COPPER IN CHLORELLA SP. (CHLOROPHYCEAE) CELLS

The green alga Chlorella sp. (strain 2350) was found to accumulate proline, up to a maximum of 0.027 fmol·cell⁻¹, under stressful concentrations of cupric ions. The function of the accumulated proline was studied with respect to its effect on copper (Cu) uptake. By induction with salt stress, cells with various levels of intracellular proline were used for this study. It is shown that the amount of Cu taken up by the cells was reduced when the intracellular proline levels were enhanced. When proline was exogenously supplied prior to Cu treatment, the adsorption of Cu was markedly reduced. When exogenous proline was supplied after Cu treatment, it resulted in a remarkable desorption of the adsorbed Cu immediately after the addition of proline. The results of the present study indicate that proline may exert some action on the cell surface and suggest that one function of accumulated proline is to reduce the uptake of metal ions. The accumulation of proline may be related to a tolerance mechanism for dealing with Cu stress.     

PHOTOSYNTHETIC AND GROWTH RESPONSES TO SALINITY IN A MARINE ISOLATE OF NANNOCHLORIS BACILLARIS (CHLOROPHYCEAE)1

A marine unicellular alga, Nannochloris bacillaris Naumann, was studied with respect to growth, viability and photosynthesis during the steady-state and also subsequent to changes in the concentration of artificial seawater medium. Cells grew exponentially over the range of 2% to 300% artificial seawater, but more rapidly at lower salinities. In contrast to growth, photosynthesis as measured by both oxygen evolution and bicarbonate photoassimilation was not obviously inhibited for cells adapted within the range of 7% to 200% artificial seawater. In 300% artificial seawater, photosynthesis, especially bicarbonate photoassimilation, was inhibited. Osmotic shocks caused by transferring cells from 200% to 7% artificial seawater had little if any effect on growth, viability or photosynthesis. However, equal shocks in the upward direction (from 7% to 200% artificial seawater) caused long lag phases in growth, totally inhibited photosynthesis and very often led to cell death. Intermediate upward shocks were less deleterious, but did result in lags in growth.     

ENVIRONMENTAL CONTROL OF PITHOPHORA OEDOGONIA (CHLOROPHYCEAE) AKINETE GERMINATION1

Abundance of Pithophora oedogonia akinetes displayed seasonal changes, being greatest in winter and lowest in summer. Akinete abundance showed significant (P < 0.001) negative correlations with photoperiod(r = -0.53) and water temperature (r= -0.75) during the period February 1978 through June 1979. Experiments in which akinete germination was studied in response to manipulations of nutrients (NO₃-N and PO₄-P), photoperiod and temperature indicated that temperature was the primary factor regulating the timing of the vernal flush of akinete germination observed in Surrey Lake.     

EVIDENCE FOR A LACK OF PHOTOSYSTEM SEGREGATION IN CHLAMYDOMONAS REINHARDTII (CHLOROPHYCEAE)

The distribution of photosystems I and II (PSI and PSII) in cells of Chlamydomonas reinhardtii Dangeard was studied by immunogold electron microscopy using cultures grown autotrophically at moderate irradiance and harvested in the middle of the light period. Sections of Lowicryl-embedded cells were labeled with monospecific heterologous antisera raised against the reaction center proteins of PSI (CP1-e) or the core antenna proteins of PSII (CP40 and CP47). All three antisera labeled both the appressed and the nonappressed thylakoid membranes at essentially similar densities. Labeling with both PSI and PSII antisera was slightly more concentrated over the outer nonappressed membranes of the thylakoid bands (1.7- to 2.4-fold with anti-CP1- e and 1.5- to 1.8-fold with anti-CP47 and anti-CP40). However, since appressed membranes comprised 73% of the total thylakoid membranes, 50%–62% of the PSI and 58%–65% of the PSII labeling were localized on appressed membranes. We conclude that photosystem distribution in C. reinhardtii is similar to that reported for other algae and different from the lateral heterogeneity observed in higher plants.     

DEGRADATIVE DISEASE IN ULVA RIGIDA (CHLOROPHYCEAE) ASSOCIATED WITH ACROCHAETE GENICULATA (CHLOROPHYCEAE)

A destructive disease affecting tank-cultivated Ulva rigida C. Agardh. was characterized by green spots, initially located at the base of the thalli, that spread through the host thallus and gradually caused perforations of the frond. The endophytic filamentous green alga Acrochaete geniculata (Gardner) O'Kelly was identified as the causative agent of the disease. The effects of this infection on the host varied from minor injuries to gross frond destruction. Advanced stages of infection resulted in frond wrinkling and severe tissue loss. These symptoms were caused by a primary compaction of the host cells due to a direct effect of the endophyte followed by secondary bacterial infections that became part of the degradative process initiated by the algal pathogen. Co-cultivation of healthy and diseased fronds resulted in transfer of the infection within 2 weeks; however, attempts to infect the host in the laboratory with actively reproducing suspensions of the endophyte were unsuccessful.     

INVERSION IN VOLVOX (CHLOROPHYCEAE)1

The asexual embryos of Volvox turn themselves inside out (invert) during development. Data presented indicate that inversion of the embryos is the result of several simple cellular shape changes, coordinated in space and time. Using whole embryos, cell groups and individual embryonic cells isolated by watchmaker's forceps and pressure on the coverslip, it was shown that the phialopore (opening) enlargement and concurrent stretching of the border cells is due to a constriction formed at the equator. However, if the posterior hemisphere is removed, this constriction no longer effects the expansion of the phialopore (which is in the anterior hemisphere) because the equatorial region is no longer anchored and has no base to support the outwardly directed force against the phialopore cells. If the posterior hemisphere is isolated several hours before inversion, the opening resulting from the incision acts as a “phialopore” and the direction of inversion is reversed. Individual cells and cells in groups undergo the same shape changes as corresponding cells in an intact embryo during inversion. This suggests that these cellular deformations are autonomous and inversion is a result of them.     

MASSIVE ACCUMULATION OF PHYTOENE INDUCED BY NORFLURAZON IN DUNALIELLA BARDAWIL (CHLOROPHYCEAE) PREVENTS RECOVERY FROM PHOTOINHIBITION1

The effects of nanomolar to micromolar concentrations of the herbicide norflurazon were studied in Dunaliella bardawil Ben-Amotz et Avron, a β-carotene-accumulating halotolerant alga. The large amount of β-carotene which Dunaliella bardawil can contain, around 8% of the algal dry weight, is reduced to 0.2% by treatment with 100 nm norflurazon. Simultaneously, phytoene is accumulated to a similar level of about 8%. The gradual increase in phqtoene content, in response to increasing norflurazon concentrations, corresponds to the decrease in β-carotene, with no evident change in other isoprenoid intermediates. Carotene-rich Dunaliella bardawil is substantially resistant to high-intensity photoinhibition. This resistance is lost in cells grown to contain low & carotene and in the nor-urazon-treated phytoene-rich cells. These obseruations are in agreement with the hypothesis that the accumulated β-carotene in Dunaliella bardawil portects the cells against injury by excessive irradiation.     

MASSIVE ACCUMULATION OF PHYTOENE INDUCED BY NORFLURAZON IN DUNALIELLA BARDAWIL (CHLOROPHYCEAE) PREVENTS RECOVERY FROM PHOTOINHIBITION1

The effects of nanomolar to micromolar concentrations of the herbicide norflurazon were studied in Dunaliella bardawil Ben-Amotz et Avron, a β-carotene-accumulating halotolerant alga. The large amount of β-carotene which Dunaliella bardawil can contain, around 8% of the algal dry weight, is reduced to 0.2% by treatment with 100 nm norflurazon. Simultaneously, phytoene is accumulated to a similar level of about 8%. The gradual increase in phytoene content, in response to increasing norflurazon concentrations, corresponds to the decrease in β-carotene, with no evident change in other isoprenoid intermediates. Carotene-rich Dunaliella bardawil is substantially resistant to high-intensity photoinhibition. This resistance is lost in cells grown to contain low β-carotene and in the norflurazon-treated phytoene-rich cells. These observations are in agreement with the hypothesis that the accumulated β-carotene in Dunaliella bardawil protects the cells against injury by excessive irradiation.     

PHYSIOLOGICAL CHANGES DURING GERMINATION OF PITHOPHORA OEDOGONIA (CHLOROPHYCEAE) AKINETES1

Akinetes of Pithophora oedogonia (Mont.) Wittrock, formed in stationary phase cultures, were induced to germinate by transfer to fresh media. Changes in various physiological parameters were monitored during the first 20 d of germination. Ungerminated akinetes contained a greater percentage of lipid, starch, and dry matter and exhibited lower photosynthetic rates than did vegetative cells. Germination consisted of four phases. Phase I (day-0 to day-1) was marked by a rapid increase in respiratory rates. Phase II (day-2 to day-6) involved protrusion of the germination tube and was insensitive to cyanide, a respiratory inhibitor, and simazine, a photosynthetic inhibitor. Phase III (day-7 to day-14) was marked by rapid elongation of the germination tube, increasing photosynthetic rate, increasing chlorophyll and water content and declining levels of lipid and starch. Germination tube elongation during phase III was not inhibited by simazine, but was cyanide sensitive. Phase IV (day-15 to day-20) was characterized by a reduction in respiratory rate and an abrupt increase in the ratio of photosynthesis to respiration. Germination tube elongation during phase IV was inhibited by simazine. The data indicate that germination in Pithophora oedogonia akinetes consists of an extensive period (phases I, II and III) during which reserve materials are respired. Utilization of internal food reserves apparently permits akinetes to germinate and supports the initial growth of the germination tube in light limited microenvironments.     

水库鱼体汞积累的预测

回归分析表明,在所研究的长江流域的１２个水库中,水库与河流鲤鱼汞含量的比值Ｆ与水库集水面积Ａ和径流量Ｑ的比值呈显著的同相关：Ｆ＝２．５０９６－０．４８０４７Ａ／Ｑ（ｒ＝－０．７９５,ｎ＝１２）凤滩水库调查结果证实了此回归方程的可靠性。实测的Ｆ值与预测值比较,相对误差为２３．１％。用此模型预测三峡大坝建成蓄水后将加剧鱼体对汞的生物富集作用,局部水域存在鱼体汞含量超过我国食品汞含量标准的可能性。本文讨     

FACTORS REGULATING THE SPATIAL DISTRIBUTION OF THE FILAMENTOUS ALGA PITHOPHORA OEDOGONIA (CHLOROPHYCEAE) IN AN INDIANA LAKE1

Pithophora oedogonia (Mont.) Wittr. biomass in Surrey Lake, Indiana was greater in the littoral than in the pelagial region. Although mean soluble reactive phosphorus concentrations did not differ between the two areas, nitrate concentrations were almost six times higher in the cove than in the open water. Using laboratory cultures of Pithophora, the half saturation constant (K_s at 20° C relating filament growth to external concentrations of nitrate-nitrogen was determined to be 1.23 mg L^?1 (=88 μM)and for phosphate-phosphorus, 0.1 mg L^?1 (=3.22 μM). These values were used to calculate a NO₃-N/PO₄-P atomic ratio of 27.6. Comparison of this value with NO₃-N/PO₄-P ratios in Surrey Lake showed that nitrogen limiting conditions were prevalent in the open water section of the lake. Alkaline phosphatase and dark ammonia uptake analyses on field collected filaments from the shallow and deep water sections confirmed the hypothesis that nitrate is the major factor limiting growth of Pithophora in Surrey Lake.