Regulation of the distribution of excitation energy in Ochromonas danica,an organism containing a chlorophyll-A/C/carotenoid light harvesting antenna

A chlorophyll a, c-fucoxanthin pigment-protein complex8 functions as the major light harvesting antenna in the Chrysophyte Ochromonas danica. The regulated distribution of excitation energy between the two photosystems was investigated in these organisms and was shown to be strongly wavelength dependent. A light state transition was induced by pre-illumination of cells using light 2 (640 nm) and light 1 (700 nm) of equal absorbed intensity, and detected by reversible changes in the 77 K chlorophyll fluorescence emission spectra. Peaks at 690 nm and 720 nm in the low temperature spectra are most likely associated with PS2 and PS1 respectively. A room temperature fluorescence emission at 680 nm induced by modulated light 2 (500 nm) was strongly quenched in the presence of background light 1 (720 nm). Removal of light 1 led to an increase in fluorescence followed by a slow quenching. The room temperature fluorescence changes were directly correlated with changes in the 77 K emission spectra that indicated a change in the distribution of excitation energy between the two photosystems. It was established that DCMU (1 mol) prevented the state 2. The conversion to state 1 followed a simple photochemical dose dependence and had a half-time of 20 s-1.5 min at 6 W m^-2. In contrast, the conversion to state 2 was independent of light intensity. These data indicate that O. danica undergoes a light state transition in response to the preferential excitation of PS2 or PS1.Abbreviations PS2 photosystem 2 - PS1 photosystem 1 - LHC light harvesting chlorophyll a/b protein - fx fucoxanthin - PQ plastoquinone - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethyl urea     

金黄滴虫细胞核微丝系统的初步观察

金黄滴虫细胞核内经常存在着许多直径约为7nm的微丝。这些徽丝大多组合成走向不定的徽丝束,微丝束交织而成遍布核内的网架。核被下面微丝束较多,它们的存在常使核被外凸而成隆脊。核内微丝与核内结构如核仁、染色质等似乎都是相连的。有些微丝横跨核被,一端位于核内,另一端位于核周腔中,并靠近叶绿体。核周腔和内质网腔中也存在着微丝和另一种纤维,印管状纤维。用细胞松弛素B处理后,细胞核、核周腔和内质网腔中的微丝均消失,细胞核的形态也发生变化,似乎微丝网架有支持细胞核的作用。核内微丝可能是在内质网中组装,然后经核周腔进入核内的。     

Studies on metabolic role of 5′-methylthioadenosine in Ochromonas malhamensis and other microorganisms

Several compounds containing a thiomethyl group were found to replace vitamin B₁₂ in a protozoan, Ochromonas malhamensis. The order of the effectiveness was as follows: 5-methylthioadenosine > S-adenosylmethionine > 5-methylthioribose > L-methionine. A similar order was obtained with respect to the permeability of these compounds into the protozoan cells, except for S-adenosylmethionine. 5-Methylthioadenosine and 5-methylthioribose as well as l-methionine markedly increased the intracellular content of l-methionine. The level of S-adenosylmethionine was also increased by them, but to a lesser degree. The thiomethyl group of the compounds was established to be incorporated into S-adenosylmethionine. The metabolic fate of the thiomethyl group of 5-methylthioadenosine cannot be distinguished from that of l-methionine. A high activity of 5-methylthioadenosine nucleosidase was detected in the cell-free extracts of the protozoan. These results strongly suggest that 5-methylthioadenosine would be metabolized to l-methionine via 5-methylthioribose and then the l-methionine would be converted to S-adenosylmethionine. Like l-methionine and vitamin B₁₂, 5-methylthioadenosine and 5-methylthioribose may play an important role in maintenance of the C-1 pool in Ochromonas malhamensis.Neither 5-methylthioadenosine nor 5-methylthioribose replaced vitamin B₁₂ in some vitamin B₁₂-requiring bacteria. This result is consistent with the fact that neither compounds was significantly taken up by these bacteria.Abbreviations MTA 5-methylthioadenosine - AdoMet S-adenosylmethionine - MTR 5-methylthioribose - TCA trichloroacetic acid Paper II in the series. The first paper of the series has been published (Sugimoto and Fukui, 1974)     

Hydrurus‐related golden algae (Chrysophyceae) cause yellow snow in polar summer snowfields

In polar regions, melting snow fields can be occupied by striking blooms of chrysophycean algae, which cause yellowish slush during summer. Samples were harvested at King George Island (South Shetland Islands, Maritime Antarctica) and at Spitsbergen (Svalbard archipelago, High Arctic). The populations live in an ecological niche, where water‐logged snow provides a cold and ephemeral ecosystem, possibly securing the survival of psychrophilic populations through the summer. A physiological adaptation to low temperatures was shown by photosynthesis measurements. The analysis of soluble carbohydrates showed the occurrence of glycerol and sugars, which may play a role in protection against intracellular freezing. Although both populations were made of unicells with Ochromonas‐alike morphology, investigation by molecular methods (18S rDNA sequencing) revealed unexpectedly a very close relationship to the mountain‐river dwelling Hydrurus foetidus (Villars) Trevisan. However, macroscopic thalli typical for the latter species were never found in snow, but are known from nearby localities, and harvested samples of snow algae exposed to dryness evolved a similar pervading, ‘fishy’ smell. Moreover, in both habitats tetrahedal zoospores with four elongate spikes were found, similar to what is known from Hydrurus. Our molecular results go along with earlier reports, where chrysophycean sequences of the same taxonomic affiliation were isolated from snow. This points to a distinct group of photoautotrophic, Hydrurus‐related chrysophytes, which are characteristic for long‐lasting, slowly melting snow packs in certain cold regions of the world.     

THE AUTOFLUORESCENT FLAGELLUM: A NEW PHYLOGENETIC ENIGMA1

Epifluorescence microscopy reveals the presence of fluorescence in the living cells of at least three classes of flagellates. In Ochromonas cells, the fluorescence is blue-green in color and is found only in the short flagellum, both in the flagellar swelling and throughout the length of the flagellum. As recognized by the locale and color of the flagellar fluorescence, the same fluorescence is observed in only certain other heterokont algal groups but is also found in one of the two isokont flagella of the prymnesiophyte Prymnesium parvum.     

Metabolism of phenols by Ochromonas danica

Abstract This study investigated the catabolic potential of a eukaryotic alga to degrade one of the most common organic pollutants, phenol. The alga, Ochromonas danica (993/28), was selected for study after screening for its heterotrophic capabilities. The catabolic versatility of the alga was elucidated by incubating with a variety of phenolic compounds. The alga removed phenol, all the cresol isomers and 3,4-xylenol from its incubation media, with phenol being removed more rapidly than any of its methylated homologues. Consequently, the alga was found to have a greater specificity for phenol than for o - or p -cresols. This study shows that O. danica could catabolize phenol and its methylated homologues.     

A TUBULAR MASTIGONEME‐RELATED PROTEIN,OCM1, ISOLATED FROM THE FLAGELLUM OF A CHROMOPHYTE ALGA,OCHROMONAS DANICA1

The phylogenetic group stramenopiles refers to the systematic groups that possess tripartite tubular hairs (stramenopiles) on their flagella. There have been a number of studies describing the fine structure of these mastigonemes and a few studies isolating the component proteins; however, these proteins and their gene sequences have not yet been identified. In the present study, we identified a mastigoneme protein (Ocm1) of the chrysophycean alga Ochromonas danica Pringsh. (UTEX LB1298). Its corresponding gene, Ocm1, was identified by using degenerate primers that correspond to the partial amino acid sequences of a protein (85 kDa) obtained from a mastigoneme‐rich fraction of isolated flagella. The polypeptide encoded by Ocm1 has four cysteine‐rich, epithelial growth factor (EGF)–like motifs, potentially involved in protein–protein interactions. It lacks obvious hydrophobic regions characteristic of transmembrane domains, suggesting that this polypeptide is not likely a protein for anchoring the mastigoneme. In addition, a polyclonal antibody against Ocm1 labeled the area where the tubular shafts of the mastigonemes are located, but not the basal portion or the terminal filaments.     

Tryptophan Metabolism in Ochromonas malhamensis

Tryptophan enhanced the growth of Ochromonas malhamensis at concentrations up to 0.4 mg/ml; higher concentrations inhibited, the growth inhibition being reversible by tyrosine and adenine. The presence of a tryptophan synthetase system in vitro was demonstrated. Tyrosine and phenylalanine stimulated the activity of this enzyme. The uptake of exogenous tryptophan was accompanied by an increase in the free tryptophan pool which in turn suppressed the tryptophan synthetase system, thus pointing to a controlled mechanism. Incorporation of tryptophan in the growth medium enhanced the biosynthesis of folate-active compounds. An elucidation of the mode of action of tryptophan is attempted on the basis of known metabolic pathways.     

金黄滴虫粘液泡的研究

用酸性粘多糖特异性染料(阿利新蓝或阿利新蓝 甲基绿)和脂肪特异性染料(如苏丹Ⅲ等)同时染活细胞,粘液泡染成蓝色,脂肪滴染成红色。活细胞的粘液泡有自发的蓝色荧光。脂肪滴无荧光。用含有阿利新蓝的戊二醛固定样品,再用O_s真O_4后固定,进行电镜观察,粘液泡呈电子致密的深黑色小泡,而脂肪滴呈灰色小泡,粘液泡的表面常盖有毛状的附属物,其形态反映了粘液泡的液体性质。在同泽的固定材料中,细胞表膜也常存在一厚层与粘液泡表面相似的毛状物质。二者应含有相同的成分,即都含有酸性粘多糖。表膜的粘多糖外被可能主要是由粘液泡向外释放的物质所形成的。电镜细胞化学的检定还表明粘液泡的表面有酸性磷酸酶的活性。粘液泡和盘状泡是同源的细胞器。     

Localization of plastid DNA replication on a nucleoid structure

Plastids contain multiple copies of the plastid genome that are arranged into discrete aggregates, termed nucleoids. Nucleoid molecular organization and its possible role in ensuring genome continuity have not yet been carefully explored. We examined the relationship between plastid DNA synthesis and nucleoid cytology in the unicellular chrysophyte Ochromonas danica, which is useful for such work because the genomes in each plastid are arranged in a single ring-shaped nucleoid. Immunocytochemical detection of thymidine analog incorporation into replicating DNA revealed that plastid DNA synthesis occurs at several sites along the ring nucleoid simultaneously, and that all plastids of a single cell display similar replication patterns. Plastid DNA replication was observed in G1, S, and G2 phase cells. Pulse-chase-pulse labelling with two different thymidine analogs revealed that new sites are activated as cells progress through the cell cycle while some old sites continue. The double labelling patterns suggest that the individual genomes are arranged consecutively, either singly or in clusters, along the nucleoid perimeter and that the selection of which genome replicates when is a matter of chance. These observations eliminate a number of alternative hypotheses concerning plastid DNA organization, and suggest how cells might maintain a constancy of plastid DNA amount and why plastid genome variants segregate so rapidly during mitosis.