Techniques for the detection of pathogenic Cryptococcus species in wood decay substrata and the evaluation of viability in stored samples

In this study, we evaluated several techniques for the detection of the yeast form of Cryptococcus in decaying wood and measured the viability of these fungi in environmental samples stored in the laboratory. Samples were collected from a tree known to be positive for Cryptococcus and were each inoculated on 10 Niger seed agar (NSA) plates. The conventional technique (CT) yielded a greater number of positive samples and indicated a higher fungal density [in colony forming units per gram of wood (CFU.g^-1) ] compared to the humid swab technique (ST). However, the difference in positive and false negative results between the CT-ST was not significant. The threshold of detection for the CT was 0.05.10³ CFU.g^-1, while the threshold for the ST was greater than 0.1.10³ CFU^-1. No colonies were recovered using the dry swab technique. We also determined the viability of Cryptococcus in wood samples stored for 45 days at 25ºC using the CT and ST and found that samples not only continued to yield a positive response, but also exhibited an increase in CFU.g^-1, suggesting that Cryptococcus is able to grow in stored environmental samples. The ST.1, in which samples collected with swabs were immediately plated on NSA medium, was more efficient and less laborious than either the CT or ST and required approximately 10 min to perform; however, additional studies are needed to validate this technique.     

Transposable element-induced mutations of the viviparous-1 gene in maize

The viviparous-1 (vp1) locus in maize is a developmental gene that controls diverse aspects of the maturation phase of seed development. Mutations of vp1 alter embryo sensitivity to the hormone abscisic acid and block formation of anthocyanin pigment. Molecular cloning of a Robertson Mutator-induced mutant allele, vp1-mum-1, by transposable element tagging has allowed analysis of several transposon-induced vp1 mutants. In the vp1-Mc mutation, the gene is disrupted by 4.0 kbp insertion, which results in expression of a 3′ truncated mRNA. Phenotypically, this allele is at least partially functional in causing embryo dormancy, but is ineffective in controlling anthocyanin expression. This result suggests that disruption of the C-terminal domain of the Vp1 protein specifically affects regulation of the anthocyanin pathway. A second Mutator- derived allele, vp1-mum2, exhibits an unusual form of somatic mutability in which endosperm cells revert from wild-type vp1 expression to a mutant condition. The vp1-mum2 allele contains a 1.5 kbp Insertion that has no detectable homology to known Mu elements. This element is retained In wild-type germinal revertants derived from vp1-mum2 An apparent DNA modification affecting cleavage at an internal Sstl restriction site in the element correlates with vp1-mum2 states that exhibit wild-type Vp1 expression. A model involving mitotic assortment of modified and unmodified DNA strands during development is proposed for vp1-mum2 somatic mutation.     

Inhibition of ribulose-1,5-bisphosphate carboxylase/oxygenase by ribulose-1,5-bisphosphate epimerization and degradation products

Xylulose-1,5-bisphosphate in preparations of ribulose-1,5-bisphosphate (ribulose-P₂) arises from non-enzymic epimerization and inhibits the enzyme. Another inhibitor, a diketo degradation product from ribulose-P₂, is also present. Both compounds simulate the substrate inhibition of ribulose-P₂ carboxylase/oxygenase previously reported for ribulose-P₂. Freshly prepared ribulose-P₂ had little inhibitory activity. The instability of ribulose-P₂ may be one reason for a high level of ribulose-P₂ carboxylase in chloroplasts where the molarity of active sites exceeds that of ribulose-P₂. Because the K_D of the enzyme/substrate complex is ≤1 μM, all ribulose-P₂ generated in situ may be stored as this complex to prevent decomposition.     

Differences among immune complexes: association of C1q in SLE immune complexes with renal disease

Studies that made use of multiple assay systems demonstrated increased levels of immune complexes (IC) in patients with systemic lupus erythematosus (SLE), but no consistent correlations of IC concentration to patterns or activity of disease have been observed. Furthermore, consistent associations between qualitative differences in IC and disease manifestations have been elusive. IC interaction with erythrocytes and mononuclear phagocytic cells is another variable in SLE that may also mediate some of the biological effects of IC. The present report concerns studies of the composition of purified IC obtained from individuals with SLE and other rheumatic diseases; a 64,000 dalton component identified as the A-B subunit of C1q was detected in purified IC from 27 of 51 SLE patients (53%). The presence of this 64,000 dalton component was not related to either IC concentration or to the serum C1q level. However, the presence of the C1q component in isolated SLE IC did correlate with the presence of renal disease (p less than 0.02). These observations are interpreted relative to a recently described kinetic model of IC clearance.     

Dominant expression of an amino-acid uptake deficiency in carrot somatic fusion hybrids

Somatic hybrids were selected previously by their ability to grow in medium containing normally inhibitory levels of the two amino acid analogs aminoethylcysteine (AEC) and 5-methyltryptophan (5MT) following fusion of protoplasts from a cell strain resistant to AEC with protoplasts resistant to 5MT. The hybrid nature of the selected clones was shown by several criteria including the presence of another resistance, azetidine-2-carboxylate (A2C), carried by one of the parental strains which was not selected for in the initial hybrid selection scheme. The characterization presented here shows that the AEC resistance in the parental strain, as well as the two somatic hybrids, was due to decreased AEC uptake. Also the 5MT resistance in the hybrids, as in the parent was caused by a feedback altered form of the tryptophan biosynthetic control enzyme, anthranilate synthase which leads to increases in free tryptophan. The A2C resistance was caused by the accumulation of free proline by a mechanism which has not been studied. These studies confirm that AEC resistance caused by decreased uptake can be expressed dominantly in protoplast fusion hybrids.Abbreviations A2C Azetidine-2-carboxylate - AEC Aminoethylcysteine - 5MT 5-methyltryptophan