NEW ULTRASTRUCTURAL ASPECTS OF PYRENOIDS OF THE LICHEN PHOTOBIONT TREBOUXZA (MICROTHAMNIALES,CHLOROPHYTA)1

The pyrenoid structure of Trebouxia, a photobiont of two lichen species, Umbilicaria cinereorufescens (Schaer.) Frey and Parmelia sulcata Taylor, was investigated. In both lichen species, the pyrenoid of the photobiont exhibited straight, unbranched, long or short tubules. In the first lichen species, multiple pyrenoids were observed occasionally, while in the second one, homogeneous masses, called protein bodies, appeared between the thylakoids. These protein bodies were previously observed in some other species of the family Umbilicariaceae. Serial sections from single pyrenoids showed that tubules of the Impressa-type pyrenoid were closely associated with pyrenoglobuli. The three-dimensional reconstruction of a complete chloroplast of a P. sulcata algal cell showed that the protein bodies were spatially separate structures. Immunolocalization techniques to detect the presence of ribulose-bisphosphate carboxylase (Rubisco) in the chloroplast showed that this enzyme was present primarily in the pyrenoid matrix. When protein bodies were present in the chloroplast, Rubisco appeared to be localized in these structures. The presence of pyrenoid satellites and protein bodies with reactivity to anti-Rubisco may be related to the nutritional conditions of the thalli.     

THE ULTRASTRUCTURE OF LICHENS. I. A GENERAL SURVEY

The fine structure of 10 lichens was examined. A comparison was made of the storage products of the algal symbiont (Trebouxia) in situ in the desiccated and hydrated states of the lichens. All the Trebouxia phycobionts, with the exception of that in Usnea strigosa, had lipid-containing globules in the pyrenoid. The globules were present in both the hydrated and desiccated conditions. Trebouxia in the hydrated condition contained starch granules in the chloroplast as well as the lipid-containing globules in the pyrenoid. The cell wall of Trebouxia consists of an outer electron-dense layer and an inner electron-light layer. Fungal haustoria (in Lecanora rubina) rupture the outer layer of the algal cell wall and invaginate the inner layer. A thick polysaccharide fibrillar material surrounds the fungal cells. Many bacteria were observed within this material. Septa and lomasomes are described. Ellipsoidal bodies, which appear to be an integral and unique part of the lichen fungal ultrastructure, were observed associated with membrane profiles.     

Ingestion,digestion, and egestion in Spongilla lacustris (Porifera,Spongillidae) after pulse feeding with Chlamydomonas reinhardtii (Volvocales)

Summary The route followed by food particles in Spongilla lacustris was clarified by light and electron microscopic examination of sponges fed with Chlamydomonas reinhardtii. The algal cells are phagocytosed by prosendopinacocytes and choanocytes. After some time they are transferred to archaeocytes, amoebocytes, and lophocytes. Changes in algal structure during digestion were observed and the egestion of algal remnants was documented in life for the first time. In light micrographs, digestion of the algal cells is manifest first in shrinkage of the cells, then in disintegration to form several spherical green fragments 2–3 m in diameter, and finally, after 12–18 h, in a reddish brown discoloration of the fragments. Signs of the digestive process in electron micrographs include disappearance of the cell-wall layers, the flagella, and the pyrenoid and its starch sheath, as well as a progressive increase in the density of the cytoplasm and karyoplasm.     

Fine structure of the blue-green phycobiont and its relation to the mycobiont in two Gonohymenia lichens

Summary Electron micrographs of the two closely related lichen species Gonohymenia mesopotamica and G. sinaica were examined. It was found that the fine structure and cytokinesis of the phycobiont, Gloeocapsa sp. are not radically different from those of non-lichenized related blue-green algae. The single dissimilarity noted is the lack of polyglucoside bodies in the lichenized state. The contact between the symbionts is by fungal penetration into the algal component, whereby the integrity of both the fungal wall and the four-lamellar structure of the algal cell wall are preserved. Environmental conditions seem to have no effect on the fungus-alga relationship.Grateful acknowledgement is made to the Israel National Academy of Science for the support of this work.     

Ultrastructural changes in the pyrenoid of the lichenParmelia sulcata stored under controlled conditions

Summary Observations have been made on ultrastructural changes in pyrenoids of the algal cells in the lichenParmelia sulcata subjected to a range of controlled desiccation and rehydration regimes. Weaker staining of parts of the proteinaceous pyrenoid matrix, interpreted as damage, occurred within 48 hours of transfering moist thalli to 53% r.h. in a 12 hours light 12 hours dark (20°C 14°C) regime. No specific damage resulted from direct dehydration at 0% r.h. or on transfer after 48 hours from 53% r.h. to 0% r.h. Material stored dry under different conditions,e.g., 0%, 53% or 53% to 0% r.h., for 72 hours showed recovery of the pyrenoid matrix when rehydrated in water (30 minutes) or by storage at 100% r.h. for 24 hours. After storage at 53% r.h. or 0% r.h. for 3 months, damage was more extreme, being greater in material originally dried at 53% r.h. Recovery in water, to the original appearance, only occurred after rehydration for 24 hours at 100% r.h. After 3 months desiccation, damage, due to the initial 48 hours at 53% r.h. was still apparent. Severe damage involved expansion of the pyrenoid. As rehydration restored pyrenoids to their original dimensions, pyrenoid proteins probably became dispersed rather than degraded during desiccation.     

The structure and histochemistry of sclerotia ofSclerotinia minor Jagger

Summary A detailed histochemical investigation was carried out on rind, cortical and medullary hyphae of sclerotia ofSclerotinia minor Jagger. Four developmental stages, including mature sclerotia, were studied. The walls and septa of all hyphae contained chitin and -1,3 glucans, while those of the rind contained in addition, a melanin-like pigment. An extracellular matrix, which accumulated around cortical and medullary hyphae, consisted primarily of -1,3 glucans, although another polysaccharide, which could not be identified by histochemical methods, was also present. Phenolic material was deposited around the extracellular matrix and in the few interhyphal spaces that remained at maturity. Glycogen was present throughout the cytoplasm of hyphae of the cortex and medulla, at all stages of their differentiation. Polyphosphate granules were laid down within small vacuoles and as sclerotia matured, became most common in the cortical region. Protein bodies developed rapidly in cortical and medullary hyphae until at maturity, they were the most obvious interhyphal feature. These bodies were either round or elongated in shape, the elongated ones often lying parallel to the long axis of the hyphae, and in close association with strands of endoplasmic reticulum. No lipid reserves were detected.Mrs. S.Lowry.     

ULTRASTRUCTURE OF VEGETATIVE AND DIVIDING CELLS OF THE UNICELLULAR RED ALGAE RHODELLA VIOLACEA AND RHODELLA MACULATA1

Rhodella violacea (Kornmann) Wehrmeyer and Rhodella maculata Evans were investigated for ultrastructural details of vegetative and dividing cells. Rhodella violacea has a nuclear projection into the pyrenoid similar to that found in R. maculata, although the nuclear projection in R. maculata traverses a starch-lined area before contacting the pyrenoid. Unlike most, red algae, the two Rhodella species lack a peripheral encircling thylakoid in the chloroplast and have dictyosomes associated solely with endoplasmic reticulum (ER) instead of with both mitochondria and ER. Both species also have a well-developed peripheral system of ER connected to the plasmalemma by tubules, a situation found only in red algal unicells, Cell division was studied primarily in R. violacea; a less thorough examination of R. maculata showed no essential differences. Both have small, double-ringed, nucleus-associated organ files (NAOs) surrounded by moderately electron-dense material, metaphase–anaphase polar gaps in the nuclear envelope, absence of perinuclear ER. and short interzonal spindles. This pattern of mitosis is similar in most respects to that reported in the unicell Flintiella. Following mitosis, microtubules extend from the region of each NAO to its associated nucleus and to the undivided pyrenoid. The NAOs appear to apply tension to the nuclei and the pyrenoid and may be the mechanism for ensuring equal partitioning of both organdies. Two different forms of pyrenoid-nucleus association occur during mitosis. Nuclear projections into the pyrenoid, prevalent during interphase and early stages of mitosis, recede at metaphase. Then, the pyrenoid extends protrusions into the nuclear polar areas, forming a cup that partially surrounds the nucleus. Cell division and vegetative characters confirm the close taxonomic affinity of these two species of Rhodella and support their separation from the genus Porphyridium.     

Asterochloris phycobiontica,gen. et spec., nov., der Phycobiont der FlechteVaricellaria carneonivea

Varicellaria carneonivea is lichenized withAsterochloris phycobiontica, a new member of theChlorococcales. In the free-living state this species reproduces by zoo- and aplanospores; autospores are lacking. Sporangia develop an internal local thickening of the wall, which marks the later aperture. A group of dictyosomes apparently contributes to the formation of this thickening. Secondary carotenoids dissolved in droplets or irregular masses of oil are deposited around and within the pyrenoid.

     

Über denChlorella-Phycobionten vonTrapelia coarctata

Trapelia coarctata is lichenized withChlorella saccharophila var.ellipsoidea; this is in accordance with one of two former statements. The cells of the isolated alga may be covered individually by a gelatinous envelope; they also can be embedded in confluent mucilage. The course of succedanous divisions leading to the formation of autospores starts with the appearance of a second, new pyrenoid and goes on with bipartioning of the chloroplast, nuclear division and cytokinesis. Starch grains identical to those in the stroma surround the pyrenoid more or less loosely and not in the form of saucer-shaped parts constituting a coherent shell.

     

ULTRASTRUCTURE OF THE LICHEN COENOGONIUM INTERPLEXUM NYL.

Coenogonium interplexum Nyl. is a green to yellow-orange filamentous lichen commonly found on tree bark, rocks, and soil. The mycobiont is the ascomycetous fungus Coenogonium. The ultrastructure of the lichenized phycobiont, Trentepohlia, closely resembles that of the non-lichenized form, a filamentous subaerial green alga. The mycobiont has a typical fungal ultrastructure, and the cell wall sometimes appears thinner at points of contact with the phycobiont wall. Several branched fungal hyphae are usually randomly arranged around a Trentepohlia filament, and may in some cases completely ensheath the alga. Although no haustoria were observed, this relationship may still be termed a lichen since there is some modification of the alga and the lichen is structurally distinct from the two symbionts.     

New and known taxa ofChlorella (Chlorophyceae): Occurrence as lichen phycobionts and observations on living dictyosomes

The algal partner of the lichenPseudocyphellaria carpoloma is a newChlorella species,Chl. sphaerica. It has a saucer- or band-shaped parietal to subparietal chloroplast with a spherical pyrenoid surrounded by a shell of starch. In some of the fully grown cells two dictyosomes lying parallel to each other and changing their position can be observed in the living state. Reproduction occurs by up to 16 autospores. 8 otherPseudocyphellaria species are also lichenized withChlorella phycobionts, apparently belonging toChl. sphaerica. The phycobiont ofWoessia fusarioides belongs toChlorella saccharophila var.ellipsoidea, and to a strain which is morphologically almost identical to one formerly isolated from the lichenTrapelia coarctata. Its ability to gather granules of india ink on the surface of young cells is one of the remarkable characters differentiating it from the latter. In the lichen thallus its cells are regularly penetrated by fungal haustoria.     

Self-supporting artificial system of the green alga <Emphasis Type="Italic">Chlamydomonas reinhardtii</Emphasis> and the ascomycetous fungus <Emphasis Type="Italic">Alternaria infectoria</Emphasis>

A long-living (of up to several years) bipartite system was constructed between the unicellular green alga Chlamydomonas reinhardtii and the ascomycetous fungus Alternaria infectoria. The metabolic cooperation between the two organisms was tested with infecting A. infectoria hyphae into nitrogen starving yellow C. reinhardtii culture. After the infection, a slow greening process of the algal cells was observed, which was studied by measuring the increasing chlorophyll content, the appearance of chlorophyll-protein complexes – using 77 K fluorescence spectroscopy, and the measurement of photosynthetic oxygen production. Transmission electron microscopy and laser scanning microscopy images showed that no direct physical contacts were formed between the algal cells and the hyphae in the long-living symbiosis but they were joint in a mucilaginous bed allowing diffusion processes for metabolic cooperation. The increased free amino acid content of the medium of the long-living bipartite cultures’ indicated possible nitrogen supply of hyphal origin, which allowed the re-greening of the algal cells. The results of this work underline the importance of symbiosis-like stable metabolic coexistence, which ensures survival under extreme environmental conditions.     

THE PYRENOID OF SCENEDESMUS QUADRICAUDA

The development of the pyrenoid of Scenedesmus quadricauda from the time of its initiation and its subsequent activities is described in some detail. Correlation is made between the evidence from light and electron microscopy. The pyrenoid is a dynamic organelle which continues to change its appearance throughout the development of the algal cell due to the following factors: the deposition of starch platelets within the periphery of the expanding matrix; the separation of starch grains into individual pockets by the intrusive growth of the chloroplast lamellae in centripetal fashion; and the transition of the shape of the starch from concavo-convex platelets to lenticular grains. By these processes starch grains are continuously formed by deposition of carbohydrates within the matrix. The grains accumulate within the chloroplast, maintaining an organic connection with each other by slender starch bridges. Some parental starch grains are passed on to daughter cells during cell division. By taking into account the planes of cleavage during cell division, it is not difficult to see that pyrenoid starch grains could become distributed throughout the daughter chloroplast, regardless of their distance from the pyrenoid.     

THE FINE STRUCTURE OF THE FLAGELLAR APPARATUS OF CARTERIA1,2

The fine structure of the flagellar apparatus of 5 species of the green quadriflagellate alga Carteria is described. The 5 species can be morphologically separated into 2 groups on the bases of cell shape and ultrastructure of the pyrenoid and flagellar apparatus. Group I cells are spherical, possess many pyrenoid thylakoids, and retain a flagellar apparatus similar to that of Chlamydomonas reinhardi. The flagellar bases are oriented at approximately 90° to one another, have distal and proximal fibers, and are associated with 4 cruciately arranged microtubule bands. Cells of group II are ellipsoid, possess few pyrenoid thylakoids, and show a complex system of microtubule bands and sigmoid-shaped, electron dense rods which extend between opposite pairs of basal bodies. The basal bodies of group II cells are directed inward in a circular pattern rather than outward as in group I cells. Unlike Chlamydomonas, the distal fiber of the Carteria species is nonstriated. The proximal fiber is striated, and both distal and proximal fibers are composed of 60–80 Å diameter microfibrils.     

Elektronenoptische Untersuchungen an Flechten

Summary The substructure in the phycobionts of the genus Trebouxia from different lichens is analysed. In the group Trebouxia I and Trebouxia II a further classification according to the differentiation of the chromatophores and their pyrenoids can be made. Trebouxia I: 1. Very long thylakoids are piled together. A few thylakoids curve through the pyrenoid. 2. The thylakoids are arranged like grana- and stromathylakoids in higher plants. In the pyrenoid the thylakoids are extended to canals. Trebouxia II: 1. Long thylakoids are packed very close together. A few of them pass through the pyrenoid in regular intervals. 2. The thylakoids are single or in piles. In the pyrenoid the thylakoids are again extended to canals. 3. The thylakoids are enlarged to vesicles which extend into the pyrenoid in the same form. 4. The thylakoids show all different forms of the above mentioned differentiations.In the different types of chromatophores there are always a large number of osmiophilic plastoglobuli in the pyrenoid matrix. It is discussed whether they are a reservoir in the lipid metabolism of the lichens.     

ULTRASTRUCTURE OF VEGETATIVE ORGANIZATION AND CELL DIVISION IN THE UNICELLULAR RED ALGA DIXONIELLA GRISEA GEN. NOV. (RHODOPHYTA) AND A CONSIDERATION OF THE GENUS RHODELLA1

This study suggests that the genus Rhodella be restricted to that set of features currently observed only in Rhodella maculata Evans and Rhodella violacea (Korn-mann) Wehrmeyer, that a new genus Dixoniella be established to accommodate the unicellular red alga, Rhodella grisea (Geitler) Fresnel, Billard, Hindák et Pekár-ková, and that Rhodella cyanea Billard et Fresnel be further studied for probable reclassification. These conclusions are based on ultrastructural comparisons of Dixoniella grisea with published information on the genus Rhodella. The presence of thylakoids in the pyrenoid, a peripheral encircling thylakoid in the chloroplast, a dictyosome/nuclear envelope association, and the lack of a specialized pyrenoid/nucleus association in D. grisea separate this alga from the genus Rhodella. Cell division in D. grisea is not demonstrably different from that in Rhodella, although the unusually well-defined material of the presumptive microtubule organizing center (MTOC) made it possible to follow the development and behavior of the MTOC to a greater degree than in previously studied red algal cells. The surprising amount of conformity in cell division characters between D. grisea and the genus Rhodella prompted a comparison of cell division characteristics in all red algal unicells studied to date. All unicells show a remarkable degree of similarity except for differences in interzonal spindle length, dissimilarities in size of the nucleus-associated organelle (NAO), and the unusual NAO of Porphyridium purpureum (Bory) Drew et Ross.     

EFFECTS OF CO2 CONCENTRATION DURING GROWTH ON THE INTRACELLULAR STRUCTURE OF CHLORELLA AND SCENEDESMUS (CHLOROPHYTA)1

Effects of CO₂ concentration during growth on intracellular structure were studied with ftve species of Chlorella and Scenedesmus obliquus. Cells grown under ordinary air conditions (low-CO₂ cells) had a well developed pyrenoid surrounded by starch, while those grown under high CO₂ conditions (high-CO₂ cells) had a less developed pyrenoid or no detectable pyrenoid. Two mitochondria, one at each side of the neck of the projection of the chloroplast close to the pyrenoid, were found in low CO₂ cells of C. vulgaris 11h. Usually, lamellar stacks extended in parallel in the chloroplast of low-CO₂ cells of C. vulgaris 11h, while a grana-like structure was found in high-CO₂ cells. However, in C. pyrenoidosa, grana like structures were found more commonly in low-CO₂ cells than in high-CO₂ cells. These results suggest that development of pyrenoid starch is generally correlated with growth under low CO₂ conditions, whereas CO₂-effects on lamellar stacking are species dependent.     

Five additional genera of conidial lichen-forming fungi from Europe

Three remarkable new genera of conidial lichen-forming fungi, with pycnidial or acervular conidiomata are described and illustrated.Hastifera tenuispora gen. et spec. nov. from the South-Tyrol, Italy, is characterized by very long and narrow hyaline conidia produced in pycnidial conidiomata immersed in thalline warts.Lichingoldia gyalectiformis gen. et spec. nov. from rocks subject to inundation by freshwater in Norway has long sigmoidly curved conidia which appear to be adapted to dispersal in water.Woessia fusarioides gen. et spec. nov. from aQuercus stump in the Burgenland, Austria, has a finely granular thallus and disc-like conidiomata producing falcate conidia; this species is also of interest in that it hasChlorella as the photobiont. The recently described hyphomyceteCheiromycina flabelliformis B. Sutton is reported from Austria for the first time, and is also lichenized. Recent collections ofNigropuncta rugulosa D. Hawksw. from Austria and Italy also show that this species is lichenized rather than parasymbiotic. In all five cases the fungal hyphae of the conidiogenous structures are continuous with those in intimate contact with cells of the algal partners and the biological relationship appears to be mutualistic giving rise to stable crustose lichen thalli.     

OBSERVATIONS ON THE FINE STRUCTURE OF THE CRYPTOPHYCEAE. I. THE GENUS CRYPTOMONAS1,2

The fine structure of 3 members of the genus Cryptomonas, C. rostrella, C. reticulata, and C. calceiformis, has been examined. These species exhibit the features typical of the class Cryptophyceae. The presence of subpellicular trichocysts causes a regular folding of the periplast, and larger trichocysts are present within the gullet. The plastid contains thylacoids arranged in pairs and a prominent pyrenoid; both structures are enclosed in 4 membranes, the outermost of which is a rough endoplasmic reticulum. The nucleus, Golgi apparatus and the Corps de Maupas occupy characteristic positions within the cell, and are the most characteristic features. All these structures indicate that this algal class occupies a unique phylogenetic position.