Biochemical Aspects of Parasitism by the Angiosperm Parasites: Starch Accumulation

The investigation dealt with starch accumulation in four species of Cuscuta (Cuscuta campestris, C. indecora, C. planiflora and C. reflexa), a leafy mistletoe (Dendrophthoe falcata) and a chlorophyll-lacking root parasite (Orobanche aegyptiaca). The highest content of starch occurred In O. aegyptiaca, with a maximum of 45 per cent of dry weight Starch in Cuscuta filaments and mistletoe leaves showed a maximum of about 10 per cent of dry weight. The starch content varied along the length of the Cuscuta vine, with a maximum in the apical region. Orobanche had a higher starch content when it was still submerged than it was fully developed. Cuscuta vines did not show any marked diurnal alteration in the starch content. The content of ethanol-soluble carbohydrate was only a tenth of the starch in Orobanche, but was relatively higher in the other parasites. the neutral sugars in Cuscuta filaments were sucrose and glucose, whereas fructose was also present in mistletoe and Orobanche. Raffinose and stachyose were absent or present only ill traces in parasite tissue. Starch granules from Cuscuta and Orobanche bad ADPG/UDPG-starch synthetase activity and homogenates starch phosphorylase activity. The former enzyme appeared to be responsible for synthesis of starch and the latter for utilization. The four different species of Cuscnta, growing on alfalfa, had more or less the same activity of starch synthetase and also of phosphorylase activity. Hosts infected by Cuscuta had significantly less starch per plant than the controls. A characteristic feature of invasion by Cuscuta and Orobanche was increased phosphorylase activity in the host tissues. The protein content of the tissues of Cuscuta and Orobanche was of a lower level than that of the host shoot system or foliage, indicating that the parasite differed from the host in having a higher carbon (of starch) to nitrogen (of protein) ratio.     

Effect of environmental conditions on sclerotia and cleistothecia production in aspergillus

Summary Literature pertaining to sclerotial Aspergilli has been reviewed in brief. Observations on the effect of certain environmental conditions viz. pH, light, temperature of incubation, oxygen-deficient conditions and various relative humidity values on sclerotia production byAspergillus niger van Tieghem, (two strains),A. flavus Link (two strains),A. sclerotiorum Hüber (one strain) andA. paradoxus Fennell &Raper (one strain) and on cleistothecia production byA. nidulans (Eidam)Wint. (one strain) have been presented. Optimum pH for sclerotia or cleistothecia production was 7.5. In other respects sclerotia and cleistothecia behaved similarly. In general, condition showing maximum sclerotia or cleistothecia production was the one that showed maximum vegetative growth. Certain strains of the same species reponded differently to the same condition. Light completely inhibited sclerotia formation in one strain ofA. flavus. InA. paradoxus, in general, conditions favouring sclerotia production were those that inhibited (or retarded) the formation of conidial heads and the yellow pigment in the medium. Oxygen-deficient conditions inhibited or retarded sclerotia or cleistothecia formation. Production of sclerotia and cleistothecia increased with an increase in relative humidity values. No definite correlation could be observed between extent of sporulation and sclerotia or cleistothecia production except in case of relative humidity. Parallelism in the behaviour of sclerotia and cleistothecia production inAspergillus lends further support in favour of the hypothesis that in this genus sclerotia are sterile stromata.     

A 43 kDa DNA binding protein from the pea chloroplast interacts with and stimulates the cognate DNA polymerase.

A DNA binding protein with DNA polymerase 'accessory activity' has been identified and purified to apparent homogeneity from pea chloroplasts. This protein consists of a single subunit of 43 kDa and binds to DNA regardless of its base sequence and topology. It increases cognate DNA polymerase-primase activity in a dose dependent manner. Using solid phase protein-protein interaction trapping and co-immunoprecipitation techniques, the purified protein was found to associate with the chloroplast DNA polymerase. The chloroplast DNA polymerase also binds directly to the radioiodinated 43 kDa protein. The specific interaction between 43 kDa protein and chloroplast DNA polymerase results in the synthesis of longer DNA chains. The 43 kDa protein, present abundantly in the pea chloroplast, appears to increase processivity of the chloroplast DNA polymerase and may play an important role in the replication of pea chloroplast DNA.     

Sex chromosome polymorphism and heterogametic males revealed by two cloned DNA probes in the ZW/ZZ fish Leporinus elongatus

In order to study the divergence of teleost sex chromosomes, subtractive cloning was carried out between genomic DNA of males and females of the rainbow trout (XX/XY) and of Leporinus elongatus (ZW/ZZ). Inserts cloned in a plasmid vector were individually tested on Southern blots of DNA of males and females for sex specificity. No sex-specific insert was obtained from trout, but two out of ten inserts cloned from L. elongatus showed sex-specific patterns in this species: one corresponds to a sequence present on both Z and W chromosomes, while the other is W specific. Sequences of these two inserts show neither clear homology with other known sequences, nor an open reading frame. They cross-hybridize with the genomic DNA of Leporinus friderici, but without sex-specific patterns. Twenty-four L. elongatus adults were sexed by gonadal observation, chromosomed examination and Southern hybridization with one or the other insert. Ten males and 11 females had chromosomes and hybridization patterns typical of their sex. One ZW female was recognized as a male with the W-specific probe. This was also the case for two unusual ZW males, one having a male hybridization pattern with the other probe. These three atypical individuals may result from single genetic exchanges between four regions of the Z and the W, giving rise to three atypical W chromosomes. Finding males with such atypical heterochromosomes in a female heterogametic species may indicate that a gradual transition occurs between the heterogametic systems.     

Surface Ultrastructural Studies on Ingress and Establishment of Pseudomonas syringae pv. mori on Mulberry Leaves

P. syringae pv. mori multiplied on leaf surface and colonized particularly on the cystoliths and in the grooves of veins. The masses of bacteria were associated with necrotic spots, which appeared 9 days after inoculation. The studies also revealed that the bacterium invaded leaf tissues through cystoliths. However, it did not enter through stomata and trichomes which had commonly been observed in most of the plant pathogenic bacteria.     

Detection of Genetic Variation in Alternaria brassicae by RAPD Fingerprints

Genetic variation in fourteen isolates of Alternaria brassicae collected from different geographical regions of the world was determined by RAPD (random amplified polymorphic DNA) analysis. Twenty random primers were tried to amplify genomic DNA of A. brassicae. Based on the PCR (polymerase chain reaction) amplification of genomic DNA of A. brassicae with four oligonucleotide random primers, fingerprints were generated for each isolate and the amplifed products were compared. Using this technique, intra- and intercontinental genetic variation among isolates of A. brassicae could be distinguished.     

Monoclonal antibodies to Escherichia coli ribosomal proteins L9 and L10. Effects on ribosome function and localization of L9 on the surface of the 50 S ribosomal subunit

Monoclonal antibodies against Escherichia coli ribosomal proteins L9 and L10 were obtained and their specificity confirmed by Western blot analysis of total ribosomal protein. This was particularly important for the L9 antibody, since the immunizing antigen mixture contained predominantly L11. Each antibody recognized both 70 S ribosomes and 50 S subunits. Affinity-purified antibodies were tested for their effect on in vitro assays of ribosome function. Anti-L10 and anti-L9 inhibited poly(U)-directed polyphenylalanine synthesis almost completely. The antibodies had no effect on subunit association or dissociation and neither antibody inhibited peptidyltransferase activity. Both antibodies inhibited the binding of the ternary complex that consisted of aminoacyl-tRNA, guanylyl beta, gamma-methylenediphosphonate, and elongation factor Tu, and the binding of elongation factor G to the ribosome. The intact antibodies were more potent inhibitors than the Fab fragments. In contrast to the previously established location of L10 at the base of the L7/L12 stalk near the factor-binding site, the site of anti-L9 binding to 50 S subunits was shown by immune electron microscopy to be on the L1 lateral protuberance opposite the L7/L12 stalk as viewed in the quasisymmetric projection. The inhibition of factor binding by both antibodies, although consistent with established properties of L10 in the ribosome, suggests a long range effect on subunit structure that is triggered by the binding of anti-L9.