THE “HYSTRICHOSPHAERID” RESTING SPORE OF THE DINOFLAGELLATE PYRODINIUM BAHAMENSE,PLATF, 19062

Germination experiments demonstrate that the “hystrichosphere” called Hemicystodinium zoharyi, which previously has been found only as a microfossil organism, is the resting spore stage in the life history of Pyrodinium bahamense, a modern bioluminescent, thecate dinoflagellate. The morphology of this spore, together with new details of the thecal structure and ontogeny of P. bahamense, is described, and it is concluded that Pyrodinium is closely related to Gonyaulax but worthy of retention as a discrete genus. The geological history of P. bahamense is traceable to the Eocene through fossil occurrences of its spore, and it is suggested that additional pyrodinioid dinoflagellates which now are extinct were represented in Lower Tertiary seas by another hystrichosphere genus, called Homotryblium. Selected aspects of the physiology and ecology of modern dinoflagellate resting spores are discussed briefly with special reference to Pyrodinium.     

OBSERVATIONS ON CHYTRIDIACEOUS PARASITES OF PHANEROGAMS. XXV. PHYSODERMA JOHNSII SPARROW,A PARASITE OF CALTHA PALUSTRIS L.

The morphology of the endobiotic and epibiotic stages of Physoderma johnsii Sparrow on Caltha palustris is described. Highly characteristic of the endobiotic stage is the formation of numbers of large, narrowly pyriform cells with a tuft of rhizoids at the broader (distal) end. Early developmental features are not included since germination of the resting spore has not as yet been achieved. Reasons for maintaining this taxon distinct from older ones on Caltha palustris are given.     

OBSERVATIONS ON CHYTRIDIACEOUS PARASITES OF PHANEROGAMS. XIV. PHYSODERMA CALAMI

Physoderma calami, a chytrid (Phycomycetes), has not been studied or apparently even collected in Europe since 1895 and has never been recorded in this hemisphere. Material widely distributed in herbaria indicated it was a Physoderma but no details save color, shape, and size of resting spores were known. A study of living material from Vermont indicates resting spore germination occurs by dehiscence of a lid and production of a sporangium with zoospores. The latter may form either an epibiotic or “ephemeral” sporangial stage and zoospores, or an endobiotic one, with extensive polycentric thallus bearing turbinate cells along the rhizoids, and, as outgrowths of these turbinate cells, straw-colored, thick-walled resting spores. The latter stage produces dark-brown spots on infected parts of the host.     

INTERACTIVE EFFECTS OF COPPER AND SILICIC ACID ON RESTING SPORE FORMATION AND VIABILITY IN A MARINE DIATOM1

The toxic effects of copper on resting spore formation and viability in the marine diatom Chaetoceros protuberans Lauder were determined both with and without silicic acid added to the medium. With silicic acid available, partial inhibition of resting spore formation occurred only at the highest cupric ion activity (pCu 8.6), while the percentage of cells forming spores at pCu's 10.2 and 11.3 was nearly the same as in the controls. Without silicic acid added to the medium, sporulation was completely inhibited at pCu 8.6 and greatly inhibited, at pCu 10.2. At pCu 11.3 and in the controls, the rate of spore formation was less than 50%. The results indicate that the inhibition of resting spore formation by copper is related to the concentration of silicic acid available to cells of C protuberans. This is consistent with previous studies which show that copper toxicity during vegetative growth involves interference with silicification in diatoms and is a Junction of the silicic acid concentration of the medium. Viable resting spores of C. protuberans were still present in cultures following exposure to elevated copper concentrations during a 100-day incubation period. This indicates that resting spores can serve to enhance diatom survival in areas polluted by heavy metals.     

The role of temperature on in vivo resting spore formation of the aphid-specific pathogen Pandora nouryi (Zygomycota: Entomophthorales) under winter field conditions

Resting spore formation of Pandora nouryi within the host Myzus persicae was investigated in an open cabbage field during two winters: 2007–2008 and 2010–2011. Multivariate correlation analysis of field data revealed that weekly mean temperature was the main abiotic factor governing the probability of resting spore formation in vivo, followed by host density and mean day length, while the effect of season was insignificant. Moreover, the temperature effect on the proportions of resting spore producing cadavers in those aphids infected with P. nouryi was well fit by a logistic equation, and high proportions (0.37–0.95) were found on most of weekly sampling occasions with mean temperatures of less than 10°C. Thus, these resultant analyses support the hypothesis that temperature is the most important abiotic factor controlling P. nouryi resting spore formation in M. persicae under field situations.     

Resting spore formation in the antarctic diatoms Coscinodiscus furcatus Karsten and Thalassiosira australis Peragallo

Summary The resting spore morphology of the antarctic diatoms Coscinodiscus furcatus Karsten and Thalassiosira australis Peragallo are described. Both species form endogenous resting spores. The spore valve of C. furcatus differ from those of the vegetative cells primarily by (i) a greater convexity and (ii) a coarser and more distinctly fasciculated areolation. This resting spore is identical to the diatom traditionally identified as C. stellaris var. symbolophorus (Grunow) Jørgensen in the Antarctic. The resting spore of T. australis differs from the vegetative cells by (i) a lack of clusters of strutted processes in a modified ring on valve face, (ii) a coarser areolation and tangential rows of areolae and (iii) a narrower and more simply structured girdle. The resting spore valve of T. australis has been described as belonging to a separate species, Actinocyclus excentricus Peragallo.     

SPORE FORMATION IN THE LIFE CYCLES OF THE DIATOMS CHAETOCEROS DIADEMA AND LEPTOCYLINDRUS DANICUS1

A nitrogen limitation technique elicited the entire life cycle of the marine centric diatoms Chaetoceros diadema (Ehr.) Gran and Leptocylindrus danicus Cleve. In C. diadema the sexual cycle followed the same pattern as in the previously investigated C. didymus. Sexuality took place in narrow diameter cells, only at 2 and 5° C, and was seldom seen. Resting spore formation took place in cells of all sizes and at all temperatures at which the species grew vegetatively (2–15° C). The L. danicus life cycle is probably unique among diatoms. Nitrogen depletion induced sexuality in the entire culture at 10 and 15° C if the cell diameter was narrow (3–8 μm). Auxospore formation was followed by resting spore formation directly within the auxospore. In C. diadema, as in most centric diatoms, resting spores are not an obligate part of the life cycle, but they are in L. danicus. Resting spore formation is a versatile adaptive response in C. diadema, depending only on nitrogen depletion, although promoted by low temperatures. In L. danicus the linkage to the sexual process sharply limits conditions under which resting spores can form.     

Honey-coloured,sessile Endogone spores: II. Changes in fine structure during spore development

Summary The fine structure of honey-coloured, sessile Endogone spores is described from initiation of the mother spore to dormancy of the resting spore. Three unusual organelles occur viz. pigment granules, large crystals and selfduplicating bacteria-like organisms. The first two are very numerous, and are specifically associated with spore formation. The pigment granules are involved in the deposition of the honey-coloured wall, and change into myelin-like figures when cytoplasm moves from the mother into the resting spore. The crystals, whose function is not known, are most conspicuous just before the resting spore reaches dormancy. The bacteria-like organisms, which may be actinomycete spores living symbiotically in the fungus, multiphy greatly as the spore enters dormancy. The dormant spore contains very little cytoplasm compressed into a fine network between very large polygonal oil globules and large round bodies thought to contain a storage polysaccharide.     

OBSERVATIONS ON CHYTRIDIACEOUS PARASITES OF PHANEROGAMS. VIII. UROPHLYCTIS (PHYSODERMA) PLURIANNULATUS AND U. MAJUS

Sparrow , Frederick K. and Yamunga Lingappa . (U. Michigan, Ann Arbor.) Observations on chytridiaceous parasites of phanerogams. VIII. Urophlyctis (Physoderma) pluriannnlatus and U. majus. Amer. Jour. Bot. 47(3): 202—209. Illus. 1960.—Urophlyctis pluriannulatus, an obligate parasite of Sanicula spp., has an endobiotic phase which is strongly polycentric and produces small crateriform galls on the petioles and blades of the host leaves. The agent accomplishing infection is not known but is probably a zygote. The first cell of the parasite established in the host is the so-called “primary turbinate organ.” This becomes multinucleate, is somewhat pyriform and becomes multicellular by 2 methods: (1) by cleavage into peripheral segments; or (2) by division into cells, each with its own cell wall. Replication of the thallus is accomplished by the production of nucleated outgrowths bearing haustoria which elongate, become ribbon-like, somewhat roughened and lumened, and produce distally turbinate organs of a second order. Tertiary, etc. turbinate organs are produced in like manner. Resting spores usually form at the tip of an extremely short outgrowth from the apex of a turbinate organ. These bear a supra-equatorial crown of 7—10 branched haustoria. Rarely, monocentric thalli are formed, in which a single turbinate organ becomes converted into a resting spore. All nuclear division figures were intranuclear. The fungus produced marked enlargement of infected host cells and their nuclei, and caused division of neighboring cells. As development continues, lysis of the surrounding host walls takes place and a large cavity bearing a dense symplast and numerous host nuclei is formed, within which is the thallus of the parasite. At maturity, all traces of symplast and of fungus, except for resting spores, disappear. Urophlyctis majus, a parasite on leaves of Rumex orbiculatus, hitherto known only from its resting spore stage, has a pattern of development strikingly similar to that of U. pluriannulatus. Here, however, turbinate cells only form peripheral segments. Furthermore, the “hyphae” are smooth and without a lumen. Aside from size differences, the mature thallus with resting spores, unbranched (not branched) haustorial tufts, etc. is like that of the Sanicula parasite. The galls produced were compartmentalized, dark red to black, usually surrounded by a reddish zone, and early dropped from the leaf. No undoubted evidence of the epibiotic gametangial phase was found in either species.     

Resting spore formation ofLeptocylindrus danicus (Bacillariophyceae) during short time-scale upwelling and its significance as predicted by a simple model

Resting spore formation during short time-scale upwelling and its significance were investigated in the field and by a simple theoretical model. Field observations of spore formation ofLeptocylindrus danicus were made off Izu Peninsula, Japan. A rapid increase in ratio of resting spore to vegetative cell numbers indicated thatL. danicus formed resting spores quickly as a response to nutrient depletion in the upwelled water, although only a very low number of resting spores was found in the upwelling. A simple model was constructed to investigate the possible advantages of spore formation during short time-scale upwelling. This showed that there is a critical time-scale for resting spore formation to be advantageous. The nutrient depletion period of the upwelling off Izu was shorter than the critical time-scale determined by the model. Rapid-sinking of resting spores may increase further the critical time-scale, unless spores return with upwelling water. For short time-scale upwelling, the vegetative cell may be better suited than the resting spore for enduring a short period of nutrient depletion. Contribution from Shimoda Marine Research Center, University of Tsukuba, No. 475.     

Observations on chytridiaceous parasites of Phanerogams

Summary A reexamination of Physoderma maculare Wallroth the type species of the genus, on Alisma, confirms Clinton's (1902) account of the production of an epibiotic stage from resting spore zoospores. The latter on mature host tissue may also give rise to the endobiotic stage which bears resting spores. On seedlings, however, resting spore zoospores produce only epibiotic sporangia. The fungus could not successfully infect Sagittaria, a closely related host.Contribution No. 1152     

MORPHOLOGY AND THERMAL DEATH POINT OF OLPIDIUM BRASSICAE

The morphology of single-sporangial isolates of lettuce, tomato, mustard, and oat Olpidium brassicae (Wor.) Dang. growing in their respective hosts as well as in cowpea were compared in situ and after extraction from the roots. The sporangia, zoospores, and resting spores of all isolates were within the established limits of the species. Single exit tubes or pores predominated which means that these isolates should not be transferred to the genus Pleotrachelus. A satisfactory assay for the presence of resting spores was developed by air-drying of the roots for a week or longer. This treatment killed zoospores and vegetative sporangia, but not resting spores. Factors affecting resting spore formation were investigated unsuccessfully. The thermal death point of zoospores of mustard isolates that did not form resting spores was between 40 and 45 C for 10 min.     

THE LIFE CYCLE OF BANGIA FUSCOPURPUREA IN CULTURE. I. EFFECTS OF TEMPERATURE AND PHOTOPERIOD ON THE MORPHOLOGY AND REPRODUCTION OF THE BANGIA PHASE12

The Bangia phase of Bangia fuscopurpurea was grown in laboratory culture in a variety of photoperiod and temperature regimes. Plants of the Bangia phase grown from 2 types of asexual spores, monospores and conchospores, exhibited growth differences under similar growing conditions. Plants derived from monospores grew more rapidly and matured earlier than those derived from carpospores. Day length and temperature were found to significantly influence growth rule, maturation, and plant size. Long day lengths resulted in more rapid growth in filament length and diameter and earlier spore formation and spore release. Maximum filament length was observed in a 12/12 hr light-dark cycle at 15 C. Spore formation and release were delayed by decreasing day length or temperature. Temperature and photoperiod were also found to influence the type of spores produced by the Bangia phase. When grown at 22 C, the Bangia phase produced only monospores, which reproduced the Bangia phase. At 9 C, with photoperiods of 11 hr or more of light, the Bangia phase produced carpospores which gave rise to the alternating Conchocelis phase. The conditions under which sporogenesis occurred determined the spore type differentiated.     

Structural and developmental studies of Chlamydomyzium oviparasiticum from Rhabditis nematodes and in culture

The oomycete (Peronosporomycete) Chlamydomyzium oviparasiticum, previously recorded as a parasite of rotifer eggs, was found infecting Rhabditis nematodes in a sample of rotting garden compost. For the first time C. oviparasiticum was cultured in liquid media, which enabled more detailed studies of zoospore behaviour and facilitated the use of confocal microscopy. Rhabditis nematodes were successfully re-infected from liquid-cultured inoculum. Light (including video) microscopy and transmission electron microscopy were used to document details of thallus development, zoospore release and resting spore morphology to enable comparison with other oomycete species. This species showed several significant saprolegnialian characters such as the ‘achlyoid’ pattern of spore formation, centrifugal cleavage and structured encystment vesicles. In contrast, spore release into a transient vesicle was a peronosporalean characteristic. The thick-walled resting spores showed relatively poor cytoplasmic preservation and had a thick multi-layered wall. It was still not possible to unequivocably decide whether these were chlamydospores or parthenogenically formed oospores. The phylogenetic significance of these observations is discussed.     

OBSERVATIONS ON CHYTRIDIACEOUS PARASITES OF PHANEROGAMS. XXVII. A FURTHER STUDY OF PHYSODERMA HYDROCOTYLIDIS VIÉGAS AND TEIXEIRA

A further study of Physoderma hydrocotylidis from California on its host Hydrocotyle ranunculoides gives further details on its structure and development. EM micrographs reveal that the notably thin wall of the resting spore consists of an outer, an intermediate, and an inner layer. The complete wall thickness from measurements of these EM preparations is only 0.5 μm, the thinnest of any known Physoderma resting spore. Such resting spores germinate readily in 2–5 h by the dehiscence of a broad cap and formation of a protruding endosporganium. Zoospores from the latter infect epidermal host cells and produce either the endobiotic, polycentric rhizoidal system with tenuous filaments, turbinate cells and eventually resting spores, or a hitherto unknown epibiotic, monocentric, rhizidiaceous sporangial stage. Zoospores from the latter may all bear colorless lipid globules or all faintly orange-colored ones.     

ULTRASTRUCTURE OF CHAETOCEROS MUELLERI (BACILLARIOPHYCEAE): AUXOSPORE,RESTING SPORE AND VEGETATIVE CELL MORPHOLOGY1

The structure of the frustule of auxospores, resting spores and vegetative cells of Chaetoceros muelleri Lemm. are described with LM and SEM. Vegetative frustules are relatively small and lightly silicified, are not united into filaments, and appear unornamented under LM and SEM. The setae are circular to subcircular in transverse section with spines and puncta arranged in a spiral pattern. The resting spore and auxospore frustules are more silicified than the vegetative frustules and appear unornamented under LM and SEM. The auxospores of C. muelleri were previously unknown.     

Resting Spore Dormancy and Infectivity Characteristics of the Potato Powdery Scab Pathogen Spongospora subterranea

The soil‐borne potato pathogen Spongospora subterranea persists in soil as sporosori, which are aggregates of resting spores. Resting spores may germinate in the presence of plant or environmental stimuli, but direct evidence for resting spore dormancy is limited. A soilless tomato bait plant bioassay and microscopic examination were used to examine features of S. subterranea resting spore dormancy and infectivity. Dried sporosori inocula prepared from tuber lesions and root galls were infective after both short‐ and long‐term storage (1 week to 5 years for tuber lesions and 1 week to 1 year for root galls) with both young and mature root galls inocula showing infectivity. This demonstrated that a proportion of all S. subterranea resting spores regardless of maturity exhibit characteristics of stimuli‐responsive dormancy, germinating under the stimulatory conditions of the bait host plant bioassay. However, evidence for constitutive dormancy within the resting spore population was also provided as incubation of sporosorus inoculum in a germination‐stimulating environment did not fully exhaust germination potential even after 2.4 years. We conclude that S. subterranea sporosori contain both exogenous (stimuli‐responsive) and constitutively dormant resting spores, which enables successful host infection by germination in response to plant stimuli and long‐term persistence in the soil.     

THE INLAND CHAETOCEROS (BACILLARIOPHYCEAE) SPECIES OF NORTH AMERICA1

Five taxa of Chaetoceros occur in inland waters of North America. These most commonly occur in waters with elevated total dissolved solids in arid regions of the western United States and Canada. Chaetoceros amanita Cleve-Euler is characterized by consistently forming relatively long chains of cells and having very spinose primary resting spore valves. Chaetoceros elmorei Boyer also forms long chains of cells which are connected by evident valvar processes; spores are nearly always smooth. Chaetoceros muelleri Lemm. may form short chains with processes between sibling valves, but also produces solitary cells lacking processes. Chaetoceros muelleri var. subsalsum (Lemm.)Johansen et Rushforth is similar to the nominate but never produces cells with Processes. Both of the C. muelleri varieties produce spores with smooth primary valves. Chaetoceros simplex Ostenfeld is characterized by a noncolonial habit, cells lacking processes and the production of resting spores with warty to some what spinose primary valves.     

The explosive diversification of the diatom genus Chaetoceros across the Eocene/Oligocene and Oligocene/Miocene boundaries in the Norwegian Sea

Eocene to middle Miocene stratigraphic changes in species richness, abundance and valve size of Chaetoceros resting spores in the Norwegian Sea (DSDP Site 338) were investigated in order to understand past productivity and paleoenvironmental changes in upwelling regions. As a result, drastic resting spore events were recognized in a 6 myr interval across the Eocene/Oligocene boundary (EO Event), the Oligocene/Miocene boundary (OM Event) and in the early middle Miocene (emM Event). The EO Event was characterized by explosive diversification at both the morpho-generic and specific levels, an increase in abundance, and a decrease in valve size from the upper Eocene through the lowest Oligocene. The OM Event was defined by a two-fold increase in species richness. During the emM Event spore abundance decreased rapidly, and species richness and valve size decreased gradually. These changes may indicate changes in the nutrient supply, especially in upwelling regions. The increased species richness suggests a change from a stable water column with a constant nutrient supply in the Eocene to an unstable one with a sporadic nutrient supply by increased vertical mixing in the Oligocene, based on evaluation of the ecologic differences between dinoflagellate cysts and Chaetoceros resting spores. The role of main primary producer might have switched from dinoflagellates and/or nannoplankton in the Eocene to diatoms, especially Chaetoceros, in the Oligocene in the Norwegian Sea. Increased resting spore species richness during the OM Event may show that environmental changes such as global cooling and nutrient mixing led to a diversification of the spore producing genus Chaetoceros. The emM Event might have been affected by changes in paleoceanographic conditions, perhaps a decrease in nutrient supply. This study presents the first paleoceanographic analysis using not only the total resting spore abundance but also the abundances of individual species, and establishes the value of spore taxonomy and diatom analysis including spores.