THE NORMAL FINE STRUCTURE OF OPOSSUM TESTICULAR INTERSTITIAL CELLS

The interstitial tissue of the opossum testis includes interstitial or Leydig cells, macrophages, and small cells which morphologically resemble mesenchymal cells. The latter are thought to give rise to mature interstitial cells. The most prominent feature of the interstitial cell cytoplasm is an exceedingly abundant agranular endoplasmic reticulum. This reticulum is generally in the form of a meshwork of interconnected tubules about 300 to 450 A in diameter, but occasionally it assumes the form of flattened, fenestrated cisternae resembling those of pancreatic acinar cells, except for the lack of ribonucleoprotein particles on the surface of the membranes. The interstitial cells vary considerably in their cytoplasmic density. The majority are quite light, but some appear extremely dense, and in addition usually have a more irregular cell surface, with numerous small pseudopodia. These differences may well reflect variations in physiological state. Cytoplasmic structures previously interpreted as "crystalloids" consist of long bundles of minute parallel tubules, each about 180 A in diameter, which seem to be local differentiations of the endoplasmic reticulum. The mitochondria are rod-shaped, and contain a moderately complex internal membrane structure, and also occasional large inclusions that are spherical and homogeneous. The prominent juxtanuclear Golgi complex contains closely packed flattened sacs and small vesicles. The results of the present study, coupled with biochemical evidence from other laboratories, make it seem highly probable that the agranular endoplasmic reticulum is involved in the synthesis of the steroid hormones produced by the interstitial cell. This finding therefore constitutes one of the first functions of the agranular reticulum for which there is good morphological and biochemical evidence.     

Effects of wall shear stress and fluid recirculation on the localization of circulating monocytes in a three-dimensional flow model

There is a correlation between the location of early atherosclerotic lesions and the hemodynamic characteristics at those sites. Circulating monocytes are key cells in the pathogenesis of atherosclerotic plaques and localize at sites of atherogenesis. The hypothesis that the distribution of monocyte adhesion to the vascular wall is determined in part by hemodynamic factors was addressed by studying monocyte adhesion in an in vitro flow model in the absence of any biological activity in the model wall.

Suspensions of U937 cells were perfused (Re = 200) through an axisymmetric silicone flow model with a stenosis followed by a reverse step. The model provided spatially varying wall shear stress, flow separation and reattachment, and a three-dimensional flow pattern. The cell rolling velocity and adhesion rates were determined by analysis of videomicrographs. Wall shear stress was obtained by numerical solution of the equations of fluid motion. Cell adhesion patterns were also studied in the presence of chemotactic peptide gradients.

The cell rolling velocity varied linearly with wall shear stress. The adhesion rate tended to decrease with increasing local wall shear stress, but was also affected by the radial component of velocity and the dynamics of the recirculation region and flow reattachment. Adhesion was increased in the vicinity of chemotactic peptide sources downstream of the expansion site. Results with human monocytes were qualitatively similar to the U937 experiments.

Differences in the adhesion rates of U937 cells occurring solely as a function of the fluid dynamic properties of the flow field were clearly demonstrated in the absence of any biological activity in the model wall.     

Analysis of physiological and molecular changes in melon (Cucumis melo L.) varieties with different rates of ripening

Seven melon varieties (Alpha, Delada, Marygold, Sirio, Topper,Tornado, and Viva) known to exhibit differences in their ripeningbehaviour were used in this study. The expression of mRNAs forACC oxidase (MEL1) and phytoene synthase (MEL5), required forsynthesis of ethylene and carotenoids, respectively, and tworipening-related cDNAs (MEL2 and MEL7), of unknown function,was examined and correlated with the development of colour andsoftening of fruits. The MEL2 and MEL7 mRNAs were present andaccumulated in all varieties, indicating their importance inmelon fruit ripening. The fruits of Delada and Marygold didnot show any change in the colour of the flesh even at 50 daa(days after anthesis). All other varieties changed colour fromgreen to orange between 25–30 daa. The phytoene synthasemRNA levels in most varieties seemed to be unrelated to changein fruit flesh colour. The firmness of all the fruits was reducedsignificantly between 25 and 40 daa. The expression of ACC oxidasemRNA showed the most variation among the different varitiesand was delayed in Sirio and undetectable in Marygold fruitseven at 40 daa. Varieties with delayed expression of ACC oxidasemRNAs after anthesis also showed delayed softening during ripening.The prospects of genetic engineering and breeding for melonfruits with improved quality characteristics and extended storagelife are discussed. Key words: Cucumis melo, colour development, melon varieties, ripening genes, softening     

Delayed leaf senescence in ethylene-deficient ACC-oxidase antisense tomato plants: molecular and physiological analysis

To determine the role of ethylene during tomato (Lycopersicon esculentum Mill. cv. Alisa Craig) leaf senescence, transgenic ACC oxidase antisense plants were analysed. Northern analysis of wild-type plants indicated that ACC oxidase mRNA accumulation normally begins in pre-senescent green leaves but was severely reduced in the antisense plants. Although the levels of ethylene evolved by wild-type and transgenic leaves increased during the progression of senescence, levels were extremely low in transgenic leaves. Leaf senescence, as assessed by colour change from green to yellow, was clearly delayed by 10–14 days in the antisense plants when compared with wild-type plants. Northern analysis of the photosynthesis-associated genes, cab and rbcS, indicated that levels of the corresponding mRNAs were higher in transgenic leaves which were not yet senescing compared with senescing wild-type leaves of exactly the same age. Northern analysis using probes for tomato fruit ripening-related genes expressed during leaf senescence indicated that once senescence was initiated the expression pattern of these mRNAs was similar in transgenic and wild-type leaves. In the antisense plants chlorophyll levels, photosynthetic capacity and chlorophyll fluorescence were higher when compared with senescing wild-type plants of the same age. Photosynthetic capacity and the quantum efficiency of photosystem II were maintained for longer in the transformed plants at values close to those observed in wild-type leaves prior to the visible onset of senescence. These results indicate that inhibiting ACC oxidase expression and ethylene synthesis results in delayed leaf senescence, rather than inducing a stay-green phenotype. Once senescence begins, it progresses normally. Onset of senescence is not, therefore, related to a critical level of ethylene. The correlation between higher levels prior to senescence and early onset, however, suggests that ethylene experienced by the plant may be a significant contributing factor in the timing of senescence.     

Antifreeze polypeptides from the Newfoundland ocean pout,Macrozoarces americanus: presence of multiple and compositionally diverse components

Summary Eight major antifreeze polypeptides (AFP) were purified from the sera of Newfoundland ocean pout. Except for their approximately identical size (6,000 Dalton), these components were shown to be separate entities by their behaviour on polyacrylamide gel electrophoresis, ion exchange chromatography, gel permeation and reverse phase high performance liquid chromatography. They could also be divided into two cross-reactive, yet distinct, immunological groups. Amino acid analysis demonstrated that ocean pout AFP are different from all of the other antifreezes studied to date. The ocean pout AFP do not contain the abundance of alanine (60 mol%) found in winter flounder and shorthorn sculpin AFP nor the high half-cystine residues (8 mol%) observed in sea raven AFP. It is suggested that ocean pout AFP represent a new type of macromolecular antifreeze.Abbreviations AFGP antifreeze glycoprotein(s) - AFP antifreeze polypeptide(s) - HPLC high performance liquid chromatography - SDS sodium dodecyl sulfate - PAGE polyacrylamide gel electrophoresis     

Purification and characterization of two essential cytochromes of the thiosulphate-oxidizing multi-enzyme system from Thiobacillus A2 (Thiobacillus versutus)

Four c-type cytochromes were purified by several procedures including chromatography on DEAE-Sepharose CL-6B, Phenyl-Sepharose CL-4B and Sephadex G-75, G-100 and G-200 and chromatofocusing. Cytochrome c-551 had a pI value of 5.2 and an M_r of 260 000 consisting of six non-covalently bound polypeptides each with an M_r of 43 000, and contained four to five haems. Cytochrome c-552.5 had a pI value of 4.8 and an M_r of 56 000 consisting of two polypeptides with the same M_r 29 000, and contained two haems. Cytochromes c-551 and c-552.5 were reduced by ascorbate to about 70 and 60% of the fully dithionite-reduced values, respectively, and both were essential components in the thiosulphate-oxidizing multi-enzyme system (other components of the system were ‘enzyme A’, ‘enzyme B’ and sulphite: cytochrome c oxidoreductase). These two cytochromes functioned as electron carriers and effectors in the oxidation of thiosulphate. Some evidence suggested that cytochrome c-551 might be a specialized electron transfer component for sulphonate-sulphur oxidation. Both cytochromes could be reduced by thiosulphate in the presence of enzymes A and B. Cytochrome c-550 (basic) and cytochrome c-550 (acidic) were small proteins with M_r 15 000 and 14 000 and pI values of over 8 and 5, respectively. Their physiological role is uncertain.     

A foliicolous alga of eocene age

An ascomycete with an anamorphic state was described from Eocene age material from Henry County, Tennessee, U.S.A., as Pelicothallus villosus Dilcher. This organism is reinterpreted as an alga.     

Analysis of the effect of transplantation on morphometric and meristic characters in lake populations of the rainbow smelt,Osmerus mordax (Mitchill)

Synopsis Results of experimental transfer of rainbow smelt into lakes reclaimed by rotenone around 1960 in Maine were originally interpreted to cast doubt on the previously widely accepted hypothesis that there were two hereditarily different forms of rainbow smelt, one large and one small. Study of more recent data from some of the transplanted populations and reanalysis of the original data suggests different conclusions. The initial effect of introductions into a reclaimed lake may be accelerated and/or more prolonged growth which exceeds even interlake differences. This initial phase, however, is followed by a second phase, when the population reaches equilibrium and these effects subside. Data from phase two of the Little Concord-Shagg and Cold Stream-Coleback Lake transfers showed that the growth characteristics of the transplanted populations returned to those of the parental populations. Large differences in growth patterns were thus found only in the initial phase of the introduction. Meristic characters were little affected by transplanting.Analysis of large specimens derived from a postulated second unofficial introduction into Coleback Lake showed that they also differed significantly, having both higher gill raker and vertebral counts than the smaller smelt. This was of interest as smelt vertebral and gill raker counts usually are inversely related; hence we do not equate these for the moment with the large form of smelt known elsewhere.It is concluded that the initial interpretation of transfer experiments be delayed until conditions approaching equilibrium can be expected to exist. Further, our analysis of more recent lake transfer data has shown nothing to refute the hypothesis that there are at least two hereditarily different forms of smelt.