SCANNING ELECTRON MICROSCOPE OBSERVATINS ON ZOOSPORANGIAL ABSCISSION IN PHYCOPELTIS EPIPHYTON (CHLOROPHYA)1

Zoosporangial abscissin in asexually reproductive Phycopeltis epiphyon, Millardet, epiphytic on leaces of Osmanhus fragrans Loureiro and Sabal minor (Jacquin) Person, examined with scanning electron micrsscopy is described and compared with the process in related Cephaleuros virescens Kunze. The laeral wall of he zoosporangium-pedicel septum begins to rupure early in he abscission process and is followed by continued learing of the lateral wall and partial spliing of the septum. The zoosporangium remains attached in a hinge-like fashion to the pedicel by a portion of the lateral wall and septum. A centrally located protuberance emerges from wihin the septa of both the zoosporangium and pedicel, and together with a slight bulging of the septa, is involved in the final separation of the zoosporangium. Although there are differences in surface morphlogy of identical in P. the zoosporangia and the location of the exit pores, the process of abscission is identical in P. epiphyton and C. virescens.     

头孢藻属中国新记录种

头孢藻属(Cephaleuros)是一类寄生性藻,在分类学上位于绿藻门石莼纲橘色藻目橘色藻科。国内对头孢藻属的研究多见于它对经济作物和观赏植物的危害,而分类学研究较缺乏。为了全面系统地了解中国头孢藻属的多样性,于2012-2018年先后在多个省份采集头孢藻属标本60余份,并对其进行了形态分类学研究。结果显示,头孢藻属中国新记录种有6种,分别为:寄生头孢藻(Cephaleuros parasiticus Karsten)、德鲁特头孢藻(Cephaleuros drouetii Thompson&Wujek)、肿毛头孢藻(Cephaleuros tumidae-setae Thompson&Wujek)、散生头孢藻(Cephaleuros diffusus Thompson&Wujek)、宽阔头孢藻(Cephaleuros expansa Thompson&Wujek)、亨宁头孢藻(Cephaleuros henningsii Schmidle),对6个种的形态学特征进行了详细描述,并提供了照片资料。     

OBSERVATIONS ON THE HABIT,MORPHOLOGY AND ULTRASTRUCTURE OF CEPHALEUROS PARASITICUS (CHLOROPHYTA) AND A COMPARISON WITH C. VIRESCENS1

Cephaleuros parasiticus Karsten, an endophyte of Magnolia grandiflora L. has been examined with light, and scanning and transmission electron microscopy. The discoid thalli are composed of filaments which ramify throughout the leaf tissues beneath the epidermis. Algal filaments do not penetrate host cells, but do produce black leaf spots which have been mistaken for those caused by the fungus Glomerella cingulate (Ston.) Spauld. and Schrenk. Two distinct thallus types occur, often simultaneously on a single leaf. One bears clusters of zoosporangiate branches which seasonally emerge through the ventral (and rarely, dorsal) surface of the leaf. In contrast, the other thallus type bears gametangia which break through the dorsal leaf surface. Zoosporangia and gametangia have never been found on the same thallus. The zoosporangia are smaller than, but almost identical in shape to, those of C. virescens Kunze. Simple plasmodesmata are present in crosswalls and acetolysis indicates that little or no sporopollenin is present in the cell walls. The ultrastructure of biflagellate gametes and quadriflagellate zoospores is virtually indistinguishable from that reported for C. virescens and similar to that reported for Phycopeltis and Trentepohlia. In both gametes and zoospores there are keeled flagella, overlapping and parallel basal bodies, two 3-layered multilayered structures with microtubular splines, and two medial compound microtubular roots. Pyrenoids, eyespots, flagellar and body scales, striated roots (or rhizoplasts), and distal bands are absent. Two presumptive mating structures are present in each biflagellate gamete, and flagellar collars occur in both types of motile cells. The extreme similarity in motile cell ultrastructure revealed in this interspecific comparison parallels that similarity revealed in intergeneric comparisons.     

STEROLS OF CEPHALEUROS (TRENTEPOHLIACEAE), A PARASITIC GREEN ALGA1

24-Ethylcholesterol, 24-ethylcholesta-5,7,22-trienol, dihydrolanosterol, 24-ethylcholesta-7,22-dienol, and 4-methyl-24-ethylcholesta-7,22-dienol were identified in cultured Cephaleuros in small quantities. Cholesterol made up 19% of the total sterol. The principal sterol, making up 65% of the total sterol, was 4,24-dimethylcholest-7-enol, a new algal sterol. This is the first report of this sterol as the principal sterol of any living organism.     

Seasonal development of five Cephaleuros species (Trentepohliaceae,Chlorophyta) on the leaves of woody plants and the behaviors of their gametes and zoospores

The infection cycle of five Cephaleuros species – C. aucubae, C. biolophus, C. japonicus, C. microcellularis, and C. virescens – was clarified by investigating seasonal development and gamete and zoospore behavior at study sites in Matsue, Shimane Prefecture, Japan. Fresh thalli or lesions appeared on the leaves of various woody plants from August and continued to develop in general from April to September in the following year. Gametangia and zoosporangia matured on 2‐ and 3‐year‐old leaves. Gametes were released in C. microcellularis samples collected from late March to late May and in samples of the other four species collected from late April to late July. Zoospores were released in C. biolophus, C. japonicus, and C. virescens samples collected from mid‐May to early August. In the present study, gametes did not conjugate but germinated like zoospores to produce new plants. After inoculation with zoospores and gametes that behave as asexual spores, fresh thalli or lesions became evident in 2–5 months following inoculation and gametes and zoospores were produced on the developed thalli or lesions the following year; one cycle of the infection was completed per year in the study area.     

Morphological features and chromosome numbers in cultures of five Cephaleuros species (Trentepohliaceae,Chlorophyta) from Japan

The morphological features and chromosome numbers were examined in cultures of five species of Cephaleuros; C. aucubae, C. biolophus, C. japonicus, C. microcellularis, and C. virescens, collected from Japan. On agar media of Bold's basal medium and CA medium, radial growth of the algal colonies was vigorous in C. virescens, moderate in C. aucubae, and poor in C. microcellularis, but varied from poor to moderate in isolates of C. biolophus and C. japonicus. Filaments of C. virescens branched at an angle less than 40° and just below the cross walls, while those of the other species branched at an angle greater than 40° without relation to the cross walls. The length of filamentous cells was significantly smaller in C. microcellularis than in the other species. The chromosome number differed with the species: n = 22 in C. aucubae, n = 34 in C. biolophus, n = 18 in C. japonicus, n = 12 in C. microcellularis, and n = 24 in C. virescens. The chromosome number did not vary between isolates from filaments and gametes in C. aucubae and C. biolophus and among those from filaments, gametes, and zoospores in C. japonicus and C. virescens.     

PHRAGMOPLASTS IN CYTOKINESIS OF CEPHALEUROS PARASITICUS (CHLOROPHYTA) VEGETATIVE GELLS 1

Cytokinesis in apical cells of actively growing cultures of Cephaleuros parasiticus Karsten sporangiate thalli was examined with transmission electron microscopy. A massive, interzonal cytokinetic microtubule spindle is anchored at its poles to the medial surfaces of the daughter nuclei at telophase. Later, the daughter nuclei are widely separated and no longer associated with the interzonal spindle; however, the spindle retains its shape and becomes a distinct phragmoplast with an array of vesicles, presumably derived from dictyosomes, aligned in the division plane. Fusion of the vesicles gives rise to a thin cell plate. Some bundles of microtubules in the spindle appear to mark the sites of plasmodesmata formation, but no endoptasmic reticulum is directly involved in plasmodesmata formation. No infurrowing or phycoplast array of microtubules is involved in the cytokinesis. The relationship, if any. between the metaphase-anaphase mitotic microtubule system and the interzonal cytokinetic spindle has not been determined. Cephaleuros parasiticus isone of only four green algae now known to contain a higher plant-like phragmoplast and cytokinetic process. The observations reported can be interpreted as very strong evidence for a phylogenetic affinity between the Trentepohliaceae and the Charophyceae, but consideration of ulvophycean features of the Trentepohliaceae such as motile cell ultrastructure and life histories precludes unequivocal assignment of the family to either the Charophyceae or Ulvophyceae.     

CULTURE AND BIOCHEMICAL ANALYSIS OF A TEA ALGAL PATHOGEN,CEPHALEUROS PARASITICUS1

To assess the current situation regarding the incidence of red rust disease in tea plants, an extensive survey was conducted in southern Indian tea plantations covering different tea cultivars and agroclimatic zones. The results indicated that the incidence of disease was more severe in tea seedlings than clones in all the agroclimatic zones. On the other hand, a simple, reliable, and reproducible technique was standardized for culturing Cephaleuros parasiticus G. Karst. isolated from infected tea leaves. Ten isolates were obtained, of which two were screened based on growth rate and culture characters for further studies. Ten culture media were tested for the culturing of C. parasiticus in which Trebouxia and Bristol media were the best followed by George, Go algal, and tea leaf extract media. Variations between isolates (Valparai C. parasiticus field number 27 [VCP27], Munnar C. parasiticus field number 11 [MCP11], and University of Texas culture number 2412 [UTEX2412]) of C. parasiticus were studied based on the growth pattern, protein expression profile, and cellular constituents in the filaments. The quantitative estimation of cellular constituents showed that there was no significant difference in these constituents among isolates. The detection of amino acids in the filaments of C. parasiticus isolates showed 16 free forms and 11 bound forms. Amino acids in bound form were higher in all the isolates than in free form of amino acids. The three isolates of C. parasiticus were closely related, with bands lying between the molecular weight of 116 and 35 kDa.