Relationships among membranes in plastids of the red algaNitophyllum punctatum (Stackh.) Grev.

Summary The fine structure of plastids in the early stages of differentiation has been studied during the carposporogenesis of the red algaNitophyllum punctatum (Stackh.) Grev. A membranous body has been found in the plastidial matrix, which shows connections either with thylakoids, or with the plastidial genophore. More than one membranous body may be present and in some instances they show a morphological relationship also with the plastidial limiting membranes. The presence of such bodies has been observed also in fully differentiated plastids in a number of other red algae currently under study.It has been shown that the plastidial envelope may release in the matrix vesicles that give rise to the single thylakoids typical of the red algal plastids.The research project received the financial support of Ministero della Pubblica Istruzione (Roma).     

Plastid Replication in Vegetative Cells, Sporangia, Spores and Sporelings of Red Algae

Ultrastructural aspects of proplastid and chloroplast replicationare described as seen in sections of vegetative cells, sporangia,released spores and sporelings of the red algae Palmaria palmataand Plumaria elegans. Proplastids in apical vegetative cellsshow internal thylakoid formation from peripheral thylakoidsin both species, and proplastid formation by budding from maturechloroplasts has also been observed. Proplastid replicationby fission has been occasionally observed, and genophore divisionin the stroma of proplastids. In vegetative cells, sporangia,spores and sporelings chloroplast formation from mature plastidscan take place by elongation and fission, or by formation ofa discrete group of thylakoids which become pinched off fromthe parent chloroplast, and by irregular expansions of the parentchloroplasts with subsequent multiple fission. Plastid replication, vegetative cells, sporangia, spores, red algae     

THE FINE STRUCTURE OF THE ELECTRIC ORGAN OF TORPEDO MARMORATA

The fine structure of the electric organ of the fish Torpedo marmorata has been examined after osmium tetroxide or potassium permanganate fixation, acetone dehydration, and Araldite embedment. This organ consists of stacks of electroplaques which possess a dorsal noninnervated and a ventral richly innervated surface. Both surfaces are covered with a thin basement membrane. A tubular membranous network whose lumen is continuous with the extracellular space occupies the dorsal third of the electroplaque. Nerve endings, separated from the ventral surface of the electroplaque by a thin basement membrane, contain synaptic vesicles (diameter 300 to 1200 A), mitochondria, and electron-opaque granules (diameter 300 A). Projections from the nerve endings occupy the lumina of the finger-like invaginations of the ventral surface. The cytoplasm of the electroplaques contains the usual organelles. A "cellular cuff" surrounds most of the nerve fibers in the intercellular space, and is separated from the nerve fibre and its Schwann cell by a space containing connective tissue fibrils. The connective tissue fibrils and fibroblasts in the intercellular space are primarily associated with the dorsal surface of the electroplaque.     

A Comparative Ultrastructural Study of Cyanidium caldarium and the Unicellular Red Alga Rhodosorus marinus

The presence of nucleus, chloroplasts, mitochondria, microbodiesand a vacuole are confirmed in Cyanidium caldarium strain CCAP1355/1. Chloroplasts usually contain parallel rows of unstackedthylakoids surrounded by a peripheral thylakoid, although theconcentric arrangement has also been observed. The chloroplastenvelope consists of two closely appressed membranes which canonly be resolved after gluteraldehyde—osmium fixation.The chloroplast of Rhodosorus marinus also contains parallel,unstacked thylakoids surrounded by a peripheral thylakoid but,in addition, a prominent, stalked pyrenoid projects into thecytoplasm and is bounded by both the peripheral thylakoid andthe chloroplast envelope. This structure is covered by a capof starch grains and contains membranous vesicles in the matrix.Phycobilisomes are absent from the chloroplasts of both algae.The recognition of C. caldarium as a rhodophyte is supportedby these observations. Cyanidium caldarium, Rhodosorus marinus, chloroplast ultrastructure     

Unusual cell structures in tumor-like formations of Gracilaria (Rhodophyta)

This paper deals with electron microscopic observations on cultivated plants of the marine red alga Gracilaria verrucosa which developed simple galls; also sea collected material, without galls, had been studied. The galls showed unusual but characteristic cell structures, caterpillar-like bodies, containing rows of fusiform bodies. These were found mostly in the cytoplasm near the plastids, in one case connected with the endoplasmic reticulum, occasionally even inside the nucleus, and are described here, as far as we know, for the first time. It does not seem probable that the caterpillar-like bodies represent mitochondria or bacteria, but the hypothesis that fusiform bodies are related to virus-like structures is discussed. The normal tissues as well as the gall tissue of the laboratory plants contained, besides plastids typical for the red algae, another type of plastids characterized by tubular thylakoids.This work was supported by grants from Consiglio Nazionale delle Ricerche (Rome) and Ministero dell'Agricoltura e delle Foreste of Italy.     

From extracellular to intracellular: the establishment of mitochondria and chloroplasts.

Paracoccus and Rhodopseudomonas are unusual among bacteria in having a majority of the biochemical features of mitochondria; blue-green algae have many of the features of chloroplasts. The theory of serial endosymbiosis proposes that a primitive eukaryote successively took up bacteria and blue-green algae to yield mitochondria and chloroplasts respectively. Possible characteristics of transitional forms are indicated both by the primitive amoeba, Pelomyxa, which lacks mitochondria but contains a permanent population of endosymbiotic bacteria, and by several anomalous eukaryotic algae, e.g. Cyanophora, which contain cyanelles instead of chloroplasts. Blue-green algae appear to be obvious precursors of red algal chloroplasts but the ancestry of other chloroplasts is less certain, though the epizoic symbiont, Prochloron, may resemble the ancestral green algal chloroplast. We speculate that the chloroplasts of the remaining algae may have been a eukaryotic origin. The evolution or organelles from endosymbiotic precursors would involve their integration with the host cell biochemically, structurally and numerically.     

DEVELOPMENT OF THE DIMORPHIC CHLOROPLASTS OF SUGAR CANE

The vascular bundle sheath cells of sugar cane contain starch-storing chloroplasts lacking grana, whereas the adjacent mesophyll cells contain chloroplasts which store very little starch and possess abundant grana. This study was undertaken to determine the ontogeny of these dimorphic chloroplasts. Proplastids in the two cell types in the meristematic region of light-grown leaves cannot be distinguished morphologically. Bundle sheath cell chloroplasts in tissue with 50% of its future chlorophyll possess grana consisting of 2-8 thylakoids/granum. Mesophyll cell chloroplasts of the same age have better developed grana and large, well structured prolamellar bodies. A few grana are still present in bundle sheath cell chloroplasts when the leaf tissue has 75% of its eventual chlorophyll, and prolamellar bodies are also found in mesophyll cell chloroplasts at this stage. The two cell layers in mature dark-grown leaves contain morphologically distinct etio-plasts. The response of these two plastids to light treatment also differs. Plastids in tissue treated with light for short periods exhibit protrusions resembling mitochondria. Plastids in bundle sheath cells of dark-grown leaves do not go through a grana-forming stage. It is concluded that the structure of the specialized chloroplasts in bundle sheath cells of sugar cane is a result of reduction, and that the development of chloroplast dimorphism is related in some way to leaf cell differentiation.     

Effects of Diffusion and Topological Factors on the Efficiency of Energy Coupling in Chloroplasts with Heterogeneous Partitioning of Protein Complexes in Thylakoids of Grana and Stroma. A Mathematical Model

In this work, we studied theoretically the effects of diffusion restrictions and topological factors that could influence the efficiency of energy coupling in the heterogeneous lamellar system of higher plant chloroplasts. Our computations are based on a mathematical model for electron and proton transport in chloroplasts coupled to ATP synthesis in chloroplasts that takes into account the nonuniform distribution of electron transport and ATP synthase complexes in the thylakoids of grana and stroma. Numerical experiments allowed the lateral profiles of pH in the thylakoid lumen and in the narrow gap between grana thylakoids to be simulated under different metabolic conditions (in the state of photosynthetic control and under conditions of photophosphorylation). This model also provided an opportunity to simulate the effects of steric constraints (the extent of appression of thylakoids in grana) on the rates of non-cyclic electron transport and ATP synthesis. This model demonstrated that there might be two mechanisms of regulation of electron and proton transport in chloroplasts: 1) slowing down of non-cyclic electron transport due to a decrease in the intra-thylakoid pH, and 2) retardation of plastoquinone reduction due to slow diffusion of protons inside the narrow gap between the thylakoids of grana. Numerical experiments for model systems that differ with respect to the arrangement of thylakoids in grana allowed the effects of osmolarity on the photophosphorylation rate in chloroplasts to be explained.     

Changes in the structure and the functional state of thylakoids under the conditions of osmotic shock

The effect of osmotic shock on the ultrastructure and functions of C-class pea chloroplasts has been examined. When incubated in a non-sucrose medium for 30 s or more, thylakoids were found to pass to a stable deformed state. This state was characterized by an altered orientation of thylakoids to each other with the lumen thickness remaining the same as in the normal state. Experiments with shorter incubation periods (10–20 s) revealed a swelling of thylakoids, which probably represented an intermediate stage. The deformation of the thylakoid system was accompanied by a decrease in the non-cyclic ATP synthesis but by an increase in the rate of cyclic photophosphorylation. Besides, the deformed thylakoids demonstrated an acceleration of the basal electron transport, as well a rise in the light-induced H⁺ and imidazol uptake. The data obtained are discussed in the light of membrane interactions fixing the configuration of a thylakoid.     

Morphology and ultrastructure ofOlisthodiscus luteus (Raphidophyceae) with special reference to the taxonomy

A flattened discoid flagellate collected from the Seto Inland Sea, Japan, has been examined by light and electron microscopy. This alga agrees well withClisthodiscus luteus Carter. It has two heterodynamic flagella emerging from a furrow on the upward side of the cell that contains six to 13 yellow-green parietal chloroplasts. It does not rotate but smoothly glide while swimming. The cell has a thin periplast lying between the plasmalemma and chloroplasts. Neither lipid bodies nor mucocysts are seen in the periplast. The pyrenoid matrix being free from thylakoids is penetrated by several cytoplasmic canals from various directions. There are no vesicles of periplastidal network in the narrow space between chloroplast envelope and chloroplast ER. The ultrastructural features ofO. luteus are unique, sharing certain characters with the raphidophycean algae but others withPseudopedinella pyriformis, a unique member of the Chrysophyceae.     

A thylakoidal processing peptidase from the heterokont alga Heterosigma akashiwo

Heterokont algae such as diatoms, brown seaweeds and the raphidophyte Heterosigma akashiwo acquired their chloroplasts via a secondary endosymbiosis involving a red algal endosymbiont and a eukaryote host, resulting in chloroplasts surrounded by four membranes rather than two. The precursor of a nuclear-encoded thylakoid lumen protein, PsbO, from Heterosigma has a presequence composed of a typical ER signal peptide followed by putative stromal and thylakoid targeting domains. A processing enzyme associated with Heterosigma thylakoids cleaved the presequence (with or without the ER signal sequence) in a single step, giving a product of the size of the mature protein. Its sensitivity to a penem inhibitor and insensitivity to other protease inhibitors suggest that it is a member of the Type I signal peptidase family. Furthermore the Heterosigma enzyme appeared to have similar substrate specificity to the pea thylakoidal processing peptidase.     

DIFFERENTIATION OF THE CHLOROPLAST OF ANTHOCEROS

It has been demonstrated that the following changes accompany differentiation in the plastid of the liverwort Anthoceros eckloni. The inner membrane of the plastid folds to give rise to small vesicles which grow and may fuse to form thylakoids, i.e. flat bags. The thylakoids may "pair" to produce the doublets (thick membranes) of the grana. The doublets may be produced also by the invagination of a thylakoid. In both cases, the doublets are produced only where outside-to-outside contact of thylakoid membranes occurs, which supports the thesis that the thylakoid membranes are polarized. The thylakoids also fold outwards, anastomose, and may fuse. This results in a complicated membrane system, for which an interpretation becomes very difficult. The starch is produced in the matrix, and the pyrenoid bodies are interpreted as specialized regions of the matrix. Younger plastids have grana, but the mature plastid has so many doublets that distinct grana cannot be recognized. This interpretation of the changes which occur during the differentiation of the plastid differs radically from those of Menke (1961) and Manton (1962) who studied this same genus, but is compatible with findings in algae and angiosperms.     

ULTRASTRUCTURE OF THE GREEN ALGA DICHOTOMOSIPHON TUBEROSUS WITH SPECIAL REFERENCE TO THE OCCURRENCE OF STRIATED TUBULES IN THE CHLOROPLAST1

The ultrastructure of the siphonous green alga Dichotomosiphon tuberosus (A. Br.) Ernst is compared with that of other siphonous plants. There is a characteristic association between the Golgi bodies and endoplasmic reticulum, but. the mitochondria are not involved in the association as they are in Vaucheria and the phycomycete Saprolegnia. An unusual structure and arrangement of the chloroplasts is described as well as a previously unreported type of “striated tubule” which occurs in most if not all chloroplasts, and amyloplasts. The structure of these tubules is compared with that of other tubules recently found in green algae and higher plants. In addition, cytoplasmic microtubules arranged in the longitudinal direction of the siphon suggest a function in cytoplasmic streaming.     

Mathematical modeling of electron and protein transport, coupled with ATP synthesis in chloroplasts

A mathematical model of electron and proton transport in chloroplasts of higher plants was developed, which takes into account the lateral heterogeneity of the lamellar system. Based on the results of numerical experiments, lateral profiles of pH in the thylakoid lumen and in the narrow gap between grana thylakoids under different metabolic conditions (in the state of photosynthetic control and under photophosphorylation conditions) were simulated. Lateral profiles of pH in the thylakoid lumen and in the intrathylakoid gap were simulated for different values of the proton diffusion coefficient and stroma pH. The model demonstrated that there might be two mechanisms of regulation of electron and proton transport in chloroplasts: (1) the slowing down of noncyclic electron transport due to a decrease in the intrathylakoid pH, and (2) the retardation of plastoquinone reduction due to slow diffusion of protons inside the narrow gap between the thylakoids of grana.     

Occurrence of Cu,Zn-Superoxide Dismutase in the Intrathylakoid Space of Spinach Chloroplasts

Thylakoids obtained from intact spinach chloroplasts showedno superoxide dismutase (SOD) activity, but Cu,Zn- and Mn-SODactivities were detected in the presence of Triton X-100. Thylakoidmembranes and the lumen fraction were separated by centrifugationafter treatment of the thylakoids with a Yeda pressure cell.Cu,Zn-SOD was found in the lumen fraction. Mn-SOD was detectedin the thylakoid fraction only after addition of 1% Triton X-100.Antibody against spinach Cu,Zn-SOD did not interact with thelatent Cu,Zn-SOD in the thylakoids unless Triton was added.These results indicate that Cu,Zn-SOD occurs in the lumen inaddition to the stroma of spinach chloroplasts, and Mn-SOD bindsto the thylakoid membranes. (Received February 29, 1984; Accepted May 28, 1984)     

A FREEZE-ETCHING STUDY OF THE RED ALGA PORPHYRIDIUM

Freeze-etched cells of Porphyridium cruentum and P. aerugineum closely resemble those fixed with glutaraldehyde and post-fixed with osmium tetroxide. Freeze-etching reveals diversity in the non-membranous and membranous parts of the cell. All the membranes are asymmetrical. The application of a double-replica technique illustrates how the two sides of several cell membranes fit together. Interpretation of fracture patterns through the thylakoids and stroma leads to the suggestion that the thylakoids are composed of repeating structural units. A model of the photosynthetic apparatus is proposed. It is suggested that the thylakoids of Porphyridium and other red algae are not always “free” but can be stacked much like those of other plants.     

p-nitroacetophenoxime N-methylcarbamate,a new electron acceptor in isolated thylakoids

p-Nitroacetophenoxime N-methylcarbamate (MCPNA) is a rather potent inhibitor of the electron transfer in spinach class A chloroplasts. In isolated thylakoids, MCPNA is an electron acceptor at the level of photosystem I (PS I). It inhibits O₂ evolution in the presence of NADP and ferredoxin but not the reduction of ferricyanide. MCPNA is active as an acceptor between 3 μM and 100 μM. At concentrations higher than 300 μM, inhibition of photosystem II (PS II) occurs. MCPNA has no uncoupling effect on photophosphorylation. Reduction of MCPNA by thylakoids in the presence of light is in accordance with the E′_o of this compound (??0.57 V) and is followed by an electron transfer to O₂. This reaction probably explains the inhibitory effect of MCPNA on class A chloroplasts.     

ULTRASTRUCTURAL CYTOLOGY OF CALLUS CULTURES OF STREPTANTHUS TORTUOSUS AS AFFECTED BY TEMPERATURE

Tissue culture cells of Streptanthus tortuosus var. orbiculatus (Cruciferae) which have acquired a spherical viruslike particle located in their nucleoli, designated cell line STV, developed supergranal chloroplasts and lost the ability to differentiate vascular tissues. The effect of temperature on the ultrastructural cytology of one line of the STV tissue, STV-I, was compared with the effect of temperature on the ultrastructural cytology of tissue culture cells lacking the viruslike particles (control cell lines). At 4 C, the cellular and ultrastructural appearance of control tissue culture cells differed from that of tissue grown at 22 C by producing increased amounts of endoplasmic reticulum and dictyosomes and by reduction of chloroplast thylakoids. STV-I cells were generally moribund as a result of 4 C treatment. Chloroplast thylakoids were also reduced in control tissue following growth at 10 C and the apparent quantities of endoplasmic reticulum and dictyosomes were similar to those observed in control cells grown at the control temperature (22 C), but less than those observed in tissue subjected to 4 C. STV-I tissue grown at 10 C demonstrated increased endoplasmic reticulum and dictyosomes and reduction of polysomal configurations. The mitochondrial morphology was variable and the cells contained supergranal chloroplasts and proplastids. At the control temperature (22 C), the fine structural appearance of control tissue culture cells was typical of parenchyma cells, but STV-I cells contained mitochondria of variable morphology and two types of chloroplasts— normal and supergranal. Control tissue grown at 30 C also contained proplastids, but these proplastids contained starch in contrast to the proplastids in control tissue grown at low temperatures. The ultrastructural cytology of STV-I cells grown at elevated temperature (30 C) was characterized by enlarged mitochondria containing massive lipid bodies and the presence of protoplastids with starch and supergranal chloroplasts.     

Ascorbate in thylakoid lumen as an endogenous electron donor to Photosystem II: Protection of thylakoids from photoinhibition and regeneration of ascorbate in stroma by dehydroascorbate reductase

Photoinhibition of the electron transport activity from tyrosine Z (Y_Z) in PS II to NADP⁺in Tris-treated thylakoids was suppressed by electron donation with either diphenylcarbazide or ascorbate (AsA) during the photoinhibition treatment. This suggests that AsA prevents donor side-induced photoinhibition in vivo as an endogenous donor. AsA in the lumen is photooxidized to monodehydroascorbate (MDA) in Tris-treated thylakoids, as detected by electron spin resonance spectrometry, but not in oxygenic thylakoids. Redox analysis of pyridine nucleotide in the presence of either MDA reductase or dehydroascorbate (DHA) reductase showed that the MDA photoproduced in the lumen is disproportionated to AsA and DHA, and the DHA leaking into the stroma is reduced to AsA by DHA reductase. No leakage of MDA through the thylakoid membrane was observed. Thus, the DHA-reducing enzyme system is indispensable in maintaining AsA concentrations in chloroplasts.     

Leaf anatomy,chloroplast ultrastructure,and cellular localisation of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) and RuBPCO activase in <Emphasis Type="Italic">Amaranthus tricolor</Emphasis> L.

In Amaranthus tricolor the leaf structure included three layers of chlorenchyma on the vascular bundle periphery, namely, mesophyll cells (MSCs) with few chloroplasts, outer larger round bundle sheath cells (BSCs) with many chloroplasts in a centripetal position, and inner smaller BSCs with few chloroplasts around the vascular bundle cells. The ultra-thin sections showed that BSCs had abundant organelles, namely many large and round mitochondria with well-developed cristae in the cytoplasm. The chloroplasts in the BSCs were lens-like bodies, which seemed to be oval on cross sections. Granal and intergranal thylakoids were usually distinguished. Grana were stacked in parallel with prevailing plane of thylakoid lamellae. The chloroplasts in the MSCs appeared smaller than those in the BSCs and contained less stacked thylakoids but abundant peripheral reticulum. The ultra-thin sections of immunogold-labelled anti-ribulose-1,5-bisphosphate carboxylase/oxygenase (anti-RuBPCO) exhibited high density of RuBPCO labelling in the stroma region of chloroplasts of the BSCs. Some anti-RuBPCO immunogold particles were observed in the stromal region of MSCs chloroplasts. The anti-activase (A) immunogold-labelling indicated that RuBPCOA was mainly distributed in the stroma region of both BSCs and MSCs chloroplasts. From the chloroplast ultrastructure and localisation of RuBPCO and RuBPCOA we deduced that the photosynthetic carbon reduction cycle and the formation of assimilatory power function in both MSC and BSC chloroplasts of A. tricolor.