Interactions between Pisolithus tinctorius and its hosts: a review of current knowledge

 Pisolithus tinctorius (Pers.) Coker and Couch [Syn. = P. arhizus (Scop.: Pers.) Rauschert] (Pt) is a widespread ectomycorrhizal basidiomycete forming mycorrhizas with a variety of hosts. Developmental and functional aspects of the symbiosis are well documented and thus Pt has been adopted as a model organism for investigations of the molecular basis of ectomycorrhizal interactions. In this review of the current state of knowledge of interactions between Pt and its hosts we demonstrate that Pt displays much intraspecific heterogeneity of host specificity, physiology and the benefits the fungus can impart upon the host plant. It is not clear at present how far such heterogeneity reflects systematic segregation within Pt. Accepted: 20 May 1997     

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     

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.     

Diffusible factors are responsible for differences in nuclease sensitivity among chromatins originating from different cell types

We have examined the kinetics of nuclease digestion of chromatin from committed and uncommitted cells in experiments where the nuclei are mixed and co-digested. Cultures of the sea urchin, Arbacia punctulata, were grown to the 16-cell stage in either [3H]thymidine or [14C]thymidine and the macromere, mesomere, and micromere cell types separated. After isolation, sets of nuclei with two different blastomere types (each having different radionucleotide tagging) were mixed and co-digested with micrococcal nuclease or DNase. I. The extent of digestion was monitored by solubility in 5% perchloric acid (PCA). We find no significant differences in initial digestion rates or limit digests among the different cell types when co-digested with either nuclease. Differences in nuclease sensitivity observed when nuclei are digested separately are abolished when nuclei are probed in a mixing experiment. The results support the hypothesis that phenotypic differences in digestibility among different cell types in vitro reflect differences in chromatin-condensing factors which can diffuse between nuclei.     

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.     

Induction of ovulation with pulsatile luteinising hormone releasing hormone.

Ovulation was successfully induced with luteinising hormone releasing hormone in 28 women with hypothalamic amenorrhoea who had failed to respond to treatment with clomiphene. Luteinising hormone releasing hormone was administered in a pulsatile manner with miniaturised automatic infusion systems. The rate of ovarian follicular maturation, as monitored by serial pelvic ultrasonography, was similar to that observed in spontaneous cycles. Endocrine assessment by serial measurement of gonadotrophin, oestradiol, and progesterone concentrations showed hormone concentrations to be within the normal range. Intravenous treatment was required in only two patients, the remainder responding satisfactorily to subcutaneous infusion. All patients conceived within six cycles of treatment, and only one multiple pregnancy occurred.     

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.     

The population ecology of gammarus tigrinus (sexton) in the reed beds of the Tjeukemeer

The population ecology of Gammarus tigrinus (Sexton) was studied in the Tjeukemeer during 1969 and 1970. G. tigrinus reaches very high densities — up to 24,000/m² in parts of the study area. In 1970, the summer densities were 2–21/2 times greater than in 1969. Individuals do not grow to such large sizes in the summer as at other times of the year. Females begin to carry eggs in March or April and reproduction ceases in November. Large females have larger broods than smaller animals and the average size of the brood varies with the time of year. The egg incubation period and growth rate are dependent upon temperature. At summer temperatures females became sexually mature after about four weeks and the egg incubation period is about io days. The entire population is turned over about three times during the year. A combination of rapid growth rate, early onset of sexual maturity and high fecundity are probably responsible for the rapid spread of G. tigrinus throughout much of the Netherlands.