I read this book the same weekend that the Packers took on the Rams, and the experience of the latter event, obviously, colored my judgment. Although I abhor anything that smacks of being a handbook (like, \"How to Earn a Merit Badge in Neurosurgery\") because too many volumes in biomedical science already evince a boyscout-like approach, I must confess that parts of this volume are fast, scholarly, and significant, with certain reservations. I like parts of this well-illustrated book because Dr. Sj6strand, without so stating, develops certain subjects on technique in relation to the acquisition of judgment and sophistication. And this is important! So, given that the author (like all of us) is somewhat deficient in some areas, and biased in others, the book is still valuable if the uninitiated reader swallows it in a general fashion, realizing full well that what will be required from the reader is a modulation to fit his vision, propreception, adaptation and response, and the kind of problem he is undertaking. A major deficiency of this book is revealed by comparison of its use of physics and of chemistry to provide understanding and background for the application of high resolution electron microscopy to problems in biology. Since the volume is keyed to high resolution electron microscopy, which is a sophisticated form of structural analysis, but really morphology in a modern guise, the physical and mechanical background of The instrument and its ancillary tools are simply and well presented. The potential use of chemical or cytochemical information as it relates to biological fine structure , however, is quite deficient. I wonder when even sophisticated morphol-ogists will consider fixation a reaction and not a technique; only then will the fundamentals become self-evident and predictable and this sine qua flon will become less mystical. Staining reactions (the most inadequate chapter) ought to be something more than a technique to selectively enhance contrast of morphological elements; it ought to give the structural addresses of some of the chemical residents of cell components. Is it pertinent that auto-radiography gets singled out for more complete coverage than other significant aspects of cytochemistry by a high resolution microscopist, when it has a built-in minimal error of 1,000 A in standard practice? I don't mean to blind-side (in strict football terminology) Dr. Sj6strand's efforts for what is \"routinely used in our laboratory\"; what is done is usually well done. It's just that …

Methods in Enzymology.

Hypersaline environments with salt concentrations up to NaCl saturation are inhabited by a great diversity of microorganisms belonging to the three domains of life. They all must cope with the low water activity of their environment, but different strategies exist to provide osmotic balance of the cells' cytoplasm with the salinity of the medium. One option used by many halophilic Archaea and a few representatives of the Bacteria is to accumulate salts, mainly KCl and to adapt the entire intracellular machinery to function in the presence of molar concentrations of salts. A more widespread option is the synthesis or accumulation of organic osmotic, so-called compatible solutes. Here, we review the mechanisms of osmotic adaptation in a number of model organisms, including the KCl accumulating Halobacterium salinarum (Archaea) and Salinibacter ruber (Bacteria), Halomonas elongata as a representative of the Bacteria that synthesize organic osmotic solutes, eukaryotic microorganisms including the unicellular green alga Dunaliella salina and the black yeasts Hortaea werneckii and the basidiomycetous Wallemia ichthyophaga, which use glycerol and other compatible solutes. The strategies used by these model organisms and by additional halophilic microorganisms presented are then compared to obtain an integrative picture of the adaptations to life at high salt concentrations in the microbial world.

Strategies of adaptation of microorganisms of the three domains of life to high salt concentrations.

Osmoregulation in Dunaliella, Part II: Photosynthesis and starch contribute carbon for glycerol synthesis during a salt stress in Dunaliella tertiolecta.

Endosymbiosis creates a unique osmotic circumstance. Hosts are not only responsible for balancing their internal osmolarity with respect to the external environment, but they must also maintain a compatible osmotic environment for their endosymbionts, which may themselves contribute to the net osmolarity of the host cell through molecular fluxes and/or exchange. Cnidarian hosts that harbor intracellular dinoflagellates (zooxanthellae) are excellent examples of such a symbiosis. These associations are characterized by the exchange of osmotically active compounds, but they are temporally stable under normal environmental conditions indicating that these osmotically driven exchanges are effectively and rapidly regulated. Although we have some knowledge about how asymbiotic anthozoans and algae osmoregulate, our understanding of the physiological mechanisms involved in regulating an intact anthozoan-dinoflagellate symbiosis is poor. Large-scale expulsion of endosymbiotic zooxanthellae, or bleaching, is currently considered to be one of the greatest threats to coral reefs worldwide. To date, there has been little consideration of the osmotic scenarios that occur when these symbioses are exposed to the conditions that normally elicit bleaching, such as increased seawater temperatures and UV radiation. Here we review what is known about osmoregulation and osmotic stress in anthozoans and dinoflagellates and discuss the osmotic implications of exposure to environmental stress in these globally distributed and ecologically important symbioses.

Osmoregulation in anthozoan-dinoflagellate symbiosis.

Publisher Summary The organism responsible for the red color was described by Teodoresco and is now named Dunafieffa safina (Dunal). It is a unicellular, photosynthetic green alga which has been placed in the division, Chlorophyta. It has two equal flagella, one cup-shaped chloroplast, an anterior nucleus, an eye-spot and a pyrenoid surrounded by starch grains at the posterior end of the cell. There is no rigid cell wall. The specific characteristics of the genus are its morphology and physiology. The cell morphology is Chlamydomonad-like. Physiologically, the genus is distinguished by the ability to grow in media with high concentrations of salt. Six freshwater species of Dunafieffa have been described; all appear to be extremely rare and their inclusion within the genus is uncertain. This chapter summarizes and analyzes the often conflicting data on Dunafielfa gathered during the past 30 years, compares and contrasts Dunafieffa with other green algae, and furthers the understanding of the adaptation of Dunaliella to high salt concentrations.

Dunaliella: a Green Alga Adapted to Salt

Dunaliella tertiolecta was disrupted mechanically and resolved by centrifugation into chloro­plast- and cytosol-enriched fractions. Intact chloroplasts could not be isolated because peripheral extensions of the single large chloroplast reached almost to the flagellar pole of the cell. The chloroplast envelope was closely appressed to the plasmalemma and, because of this and its dimensions, was vulnerable to mechanical damage to the cell.Distribution of enzymes of the glycerol cycle between the two fractions was compared with that of two marker enzymes, phosphoenolpyruvate carboxylase (cytosol) and ribulose bisphosphate carboxylase (chloroplast). The two reversible steps of the cycle were found to be spatially separated; glycerol-3-phosphate dehydrogenase (NAD-specific) was located in the chloroplast whereas glycerol dehydrogenase (NADP-specific) was located in the cytosol. The distribution of the two irreversible enzymes, glycerol phosphate phosphatase and dihydroxyacetone kinase is uncertain. These enzymes might occur about equally in both major compartments (cytoplasm and chloroplast) or be mitochondrial or they might be loosely associated with a membrane system. Implications of these results for regulation of the glycerol cycle are discussed.

Osmoregulation in Dunaliella. Intracellular Distribution of Enzymes of Glycerol Metabolism

The glycerol-3-phosphate dehydrogenase (NAD-dependent) reaction was studied in a chloroplast-enriched fraction fromDunaliella tertiolecta. The reaction has widely separated pH optima for each direction. Reduction of dihydroxyacetone phosphate proceeded with Michaelis-Menten kinetics but sigmoidal double reciprocal plots were obtained with glycerol phosphate as variable substrate. NADP served as an alternative substrate but it was somewhat less effective than NAD. The reaction was inhibited by inorganic orthophosphate and by adenine nucleotides in a manner indicative of anion inhibition. Inhibition by inorganic phosphate was competitive with DHAP and possibly also with NADH. The enzyme was activated by Na+ at concentrations below 200 μm and inhibited at higher concentrations, the region of maximum activation being affected by substrate concentration. Inhibition by Na+, present as a counterion of the substrate, was evidently responsible for apparent substrate inhibition by glycerol phosphate. Several important differences were apparent between the reaction in the unfractionated chloroplast-enriched fraction and the properties of a partly purified enzyme described by Haus and Wegmann (1984a, b).In toto, the results suggest that the regulatory potential of the reaction is probably more relevant to homeostatic control of glycerol content under steady state conditions than to controlling response to water stress.

Osmoregulation inDunaliella. Catalysis of the glycerol-3-phosphate dehydrogenase reaction in a chloroplast-enriched fraction ofDunaliella tertiolecta

The response of the green halotolerant alga Dunaliella to osmotic stress: effects on adenine nucleotide contents

Dunaliella is a green wall-less unicellular alga that is able to adapt to and grow in a wide range of salt concentrations. The major osmoregulatory solute is glycerol, the metabolism of which is relatively simple, involving a two-step synthesis and dissimilation to and from dihydroxyacetone phosphate (1). However, the mechanism by which these reactions are regulated to achieve internal glycerol concentrations appropriate to maintaining a constant cell volume at different external salt concentrations is unknown. This paper describes changes in the content of some metabolites that are relevant to that question.

The Response of Dunaliella to Salt Stress: A Comparison of Effects on Photosynthesis, and on the Intracellular Levels of the Osmoregulatory Solute Glycerol, the Adenine Nucleotides and the Pyridine Nucleotides

Thérèse Marengo

Papers

Osmoregulation in Dunaliella. Intracellular Distribution of Enzymes of Glycerol Metabolism

Osmoregulation inDunaliella. Catalysis of the glycerol-3-phosphate dehydrogenase reaction in a chloroplast-enriched fraction ofDunaliella tertiolecta

The response of the green halotolerant alga Dunaliella to osmotic stress: effects on adenine nucleotide contents

The Response of Dunaliella to Salt Stress: A Comparison of Effects on Photosynthesis, and on the Intracellular Levels of the Osmoregulatory Solute Glycerol, the Adenine Nucleotides and the Pyridine Nucleotides