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We describe a novel approach to assess toxicity to the free‐living nematode Caenorhabditis elegansthat relies on the ability of firefly luciferase to report on endogenous ATP levels. We have constructed bioluminescent C. eleganswith the lucgene under control of a constitutive promoter. Light reduction was observed in response to increasing temperature, concentrations of copper, lead and 3,5‐dichlorophenol. This was due to increased mortality coupled with decreased metabolic activity in the surviving animals. The light emitted by the transgenic nematodes gave a rapid, real‐time indication of metabolic status. This forms the basis of rapid and biologically relevant toxicity tests.

The parietal cell of the gastric mucosa undergoes rapid morphological transformation when it is stimulated to produce hydrochloric acid. In chemically fixed cells, this process is seen as a reduction in number of cytoplasmic 'tubulovesicles' as the apical surface of the cell progressively invaginates to increase the secretory surface area. It is widely believed that the tubulovesicles represent stored secretory membrane in the cytoplasm of the unstimulated cell, which is incorporated into the apical membrane upon stimulation, because they share H+,K+-ATPase activity with the apical membrane. However, fusion of tubulovesicles with the apical membrane concomitant with parietal cell activation has never been convincingly demonstrated. We have used fast freeze-fixation and freeze-substitution to study stages of morphological transformation in these cells. Tubulovesicles were not seen in the cytoplasm of any of our cryoprepared cells. Instead, the cytoplasm of the unstimulated cell contained numerous and densely packed helical coils of tubule, each having an axial core of cytoplasm. The helical coils were linked together by connecting tubules, lengths of relatively straight tubule. Lengths of straight connecting tubule also extended from coils lying adjacent to the apical and canalicular surfaces and ended at the apical and canaliculus membranes. Immunogold labelling with alpha- and beta-subunit-specific antibodies showed that the gastric H+,K+-ATPase was localized to the membranes of this tubular system, which therefore represented the configuration of the secretory membrane in the cytoplasm of the unstimulated parietal cell. Stimulation of the cells with histamine and isobutylmethylxanthine lead to modification of the tubular membrane system, correlated with progressive invagination of the apical membrane. The volume of the tubule lumen increased and, as this occurred, the tight spiral twist of the helical coils was lost, indicating that tubule distension was accounted for by partial unwinding. This exposed the cores of cytoplasm in the axes of the coils as rod-shaped elements of a three-dimensional reticulum, resembling a series of microvilli in random thin sections. Conversely, treatment with the H2 antagonist cimetidine caused severe contraction of the tubular membrane system and intracellular canaliculi. Our results indicate that tubulovesicles are an artifact of chemical fixation; consequently, they cannot have a role in parietal cell transformation. From our findings we propose an alternative model for morphological transformation in the parietal cell. This model predicts cytoskeleton-mediated control over expansion and contraction of the tubular membrane network revealed by cryopreparation. The model is compatible with the localization of cytoskeletal components in these cells.

The megasporocyte of Isoetes englemanni at the leptotene-zygotene interval of meiosis contains 4 disk-shaped proplastids about 12 μm in diameter. The disposition of these organelles in the cell is such that each of the four megaspores delimited during cytokinesis contains a single proplastid. During prophase and following their incorporation into the spores, the proplastids are undergoing fission by budding. The buds are first discernible as low surface evaginations which contain a complement of granular somal material, some wefts of tubular membrane and osmiophilic globuli, in addition to a number of vesicles derived by invagination from the inner membrane of the proplastid envelope. As the evaginations emerge they enlarge and the link with the parent body is reduced to a narrow channel. At this stage one or more of the vesicles derived from the proplastid envelope comes into register with the lumen of the channel. One vesicle is transported into the lumen, elongating as it passes through. The passage of the vesicle into the channel destroys the connexion between the matrix of the évagination and the stroma of the proplastid. The occurrence in the cytoplasm around the proplastid of bodies not connected to the proplastid, but identical in structure to the evaginations and carrying a membranous tail suggests that the evaginations are released by abscission of the channel close to the surface of the parent body. After release the bodies undergo division by constriction. Regression of the tail follows division in those bodies which are regular in outline and in which the matrix is ultrastructurally similar to the stroma of the parent organelle. The process does not seem to occur in co-existing forms which have assumed an irregular outline and have a less-opaque matrix. The more mature megaspore of Isoetes contains proplastids up to 4 μm in greatest dimension. The stroma in these is dense and granular and contains membrane-bound vesicles, osmiophilic globuli, starch granules and wefts of tubular membrane. There is no evidence that the large budding organelle persists to this later stage in development. The resemblance of the plastids in the more mature megaspore to the bodies produced by évagination earlier in development suggests a common identity. The observations and interpretations lead to the proposition that the plastids in Isoetes englemanni are autonomous. This situation contrasts with the one described for another heterosporous haploid dioecious pteridophyte, Marsilea vestita, where nucleocytoplasmic interaction has been interpreted as the de novo creation of plastids and mitochondria following the elimination by autophagy of the organelles inherited at meiosis. It is suggested that an explanation to account for the 2 different mechanisms might be sought in regard to the degree of developmental success enjoyed by the individual megaspores in the 2 plants. In Isoetes all 4 megaspores of every tetrad survive and develop, while in Marsilea the mature megasporangium contains a single functional megaspore.

Ripe pollen of the primitive gymnosperm Cycas armstrongii germinates 8–15 days after sowing on a suitable artificial medium. During the pre-germination interval, the tube cell of the tricellular male gametophyte is actively engaged in the synthesis and export of polysaccharide material. This polysaccharide is laid down as a continuous microfibrillar stratum between the tube cell plasmalemma and the pollen wall intine. While the polysaccharide layer is forming, numerous evaginations arise as cytoplasmic extensions from the tube cell and penetrate the component. The structural link between the cell and the evaginations is eventually lost and the isolated fragments of cytoplasm immediately break up to form discrete particles. These particles remain within the channels previously occupied by the evaginations. At germination, the exine and intine layers of the pollen wall are disrupted and the tube cell emerges through the germinal aperture to establish the pollen tube. Polysaccharide deposition is resumed at about this stage, and consequently, a second microfibrillar layer begins to form beneath the first. The wall of the early pollen tube, therefore, has two distinct zones: the outer stratum is a loose superficial reticulum of fibrils and contains cytoplasmic inclusions; the inner stratum is structurally compact and is without inclusions. Throughout the period of tube development, the presence of protein, including the enzyme acid phosphatase, can be demonstrated in the outer wall zone with cytochemical methods. Immunofluorescent staining using pollen antiserum immunoglobulin G in an indirect technique with fluorescein isothyocyanate-labelled secondary antibody shows that one component in the pollen tube wall is immunologically related to the male gametophyte, and results from immunoelectron microscopy support the conclusion that this consists of the inclusions rather than the polysaccharide fabric of the tube wall itself. There are remarkable similarities between the cytoplasmic inclusions in the tube wall in Cycas and those found in the intine layer of flowering plant pollen. Both are of haplophase derivation, although the inclusions in the flowering plants are introduced via evaginations into the intine, the incipient pollen tube wall, at a much earlier stage in pollen development than they are in Cycas. The difference in the time of incorporation represents, perhaps, one more episode in the progressive evolutionary trend towards rapid pollen tube initiation and growth, and hence rapid fertilization, in spermatophyte pollen. This possibility is discussed, taking into account the view that the cycads and flowering plants are groups with a common ancestor.

In many flowering plant species, a system of self-incompatibility, typically controlled by a single gene with multiple alleles (S-gene)1, enables individual plants to recognize and reject their own pollen. In gametophytically determined systems, the growth of self-pollen tubes is arrested in the style or occasionally the ovary. The expression of this self-incompatibility is developmentally regulated, being strongest in mature flowers and weak in immature styles1,2. We have used a complementary DNA clone, believed to encode the S2-allele of Nicotiana alata2,3, to detect S2messenger RNA by in situhybridization to sections. We report here that expression of the gene occurs in the stigma and throughout the secretory tissue, but not in other parts, of mature pistils. In immature flowers, S2mRNA is confined to the proliferated epidermis of the stigma. We conclude that S2-gene expression correlates well with the expression of incompatibility.

Presents a strategy to beginners for becoming a competent hot rodder with the least amount of frustration and financial stress. The need to acquire the knowledge of the various systems within a car; Sources of information; Professional shops sometimes allow young people to help out. INSET: You can be a race driver; Make it safe before you make it fast....

Gives information to 1968 to 1972 Chevelle owners on modifying their car for improved performance. Engine swaps; Suspension; Shocks; Wheel and tire combinations; Body. INSET: This is the Chevelle you really want..

Reports on the Nevada Motorsports Association's (NMSA) inaugural Triathlon of Motorsports held December 7-8, 1991 at the Las Vegas International Speedway. The competition consists of a drag, oval, and race course and the winner is the one who has the lowest combined time from all three courses.

Shows the results of hot rods that have been built on a budget and highlights how the owners were able to create these machines. 1967 Cougar; 1957 Camaro; 1936 Ford pick-up truck; 1965 Mustang.

Part 2. Shows how Robert Jung of Edelbrock assembled an efficient, potent, and less polluting Chevrolet engine. Valves; Headers; Ignition system; The engine's performance.

Part I. Looks at a typical 1970s car and figures out why it produces so many exhaust emissions. The second part of the article will focus on how to clean up the emissions while still producing power. INSET: Emissions compounds.;Next month-A clean power team..

Takes a look at the 15th annual Street Machine Nationals held in Du Quoin, Ill. Paint trends; Popular interior designs; Engine choices.

Describes some of the best parts and sources for parts for building a more powerful engine. Chevy Race Shop for heads; Kenny Brown's Project Industries offers new Gold Heads; Super Power Shot plate system from NOS.

Presents a photo essay with text of the best hot rods of the Super Nationals. The Super Nationals took place May 31 through June 2, 1991 at the Canfield Fairgrounds in Canfield, Ohio.

Presents photos and descriptions of some of the nicest hot rods in the country sent in by readers. Each car is treated as an entity and not as a collection of parts.

Examines a group of scorchin', snortin', red hot trucks. Full-tilt racers; Ten-second streeters; New and old.

Offers engine building techniques for the small-block Chevy engine. Oil pump preparation; How to increase reliability in timing chain and gear set; How to improve oil flow.

Provides quick and easy ways to properly manage automotive-related hazardous materials. What happens to the materials if they are dumped in the trash or down the drain; The use of an alternative to antifreeze/coolant; The creation of recycling channels. INSET: Team `hazmat': Recycling and handling tips; Are alternative....

Investigates two of the quickest street-licensed and registered hot rods in the Detroit area, a 1969 Z/28 and a 1970 Nova. What the frames are like; How the installation of a roll cage reinforced the frame; Suspension systems; Engines; Transmissions.

Recounts the third running of the Silver State Classic Challenge that took place in late September in the high desert of Nevada. The course; Length; The speeds the cars attain.