Gametic behavior in a marine green alga, Monostroma angicava: an effect of phototaxis on mating efficiency

The role of phototactic behavior of gametes was tested experimentally in the slightly anisogamous marine green alga Monostroma angicava Kjellman, and the effect of phototaxis on mating efficiency was discovered. Both male and female gametes showed positive phototaxis in response to a white light source. In contrast, they did not respond to a red light source. Their swimming velocity did not differ between these two illuminating light sources. It was, therefore, suggested that the search ability of the gamete itself might not vary between phototactic and non-phototactic conditions. The number of zygotes formed during the mating process may be expressed as the product of the number of encounters between male and female gametes and the fraction of encounters that result in sexual fusion. In this study, with high densities of male and female gametes mixed in test tubes, almost all minor (fewer in number) gametes fused sexually within 10 min. After dilution of the gamete suspensions by half, mating efficiency in test tubes illuminated by white light from above was higher than that in dark controls. This suggests that male and female gametes gathered at the water surface through their positive phototaxis, thus increasing the rate of encounters. Mating efficiency also decreased if the test tubes were illuminated from above by white light and also shaken. Since negative phototaxis is clearly shown in planozygotes, we suggest that positive phototaxis of male and female gametes in M. angicava is an adaptive trait for increasing the rate of gametic encounters rather than for the dispersal of zygotes as previously reported for zoospores of some marine algae. Received: 12 February 1999 / Revision accepted: 24 May 1999     

Common Sequence at the 5′ Ends of the Segmented RNA Genomes of Influenza A and B Viruses

Guanylyl- and methyltransferases, isolated from purified vaccinia virus, were used to specifically label the 5′ ends of the genome RNAs of influenza A and B viruses. All eight segments were labeled with [α-³²P]guanosine 5′-triphosphate or S-adenosyl[methyl-³H]methionine to form “cap” structures of the type m⁷G(5′)pppN^m-, of which unmethylated (p)ppN- represents the original 5′ end. Further analyses indicated that m⁷G(5′)pppA^m, m⁷G(5′)pppA^mpGp, and m⁷G(5′)pppA^mpGpUp were released from total and individual labeled RNA segments by digestion with nuclease P1, RNase T1, and RNase A, respectively. Consequently, the 5′-terminal sequences of most or all individual genome RNAs of influenza A and B viruses were deduced to be (p)ppApGpUp. The presence of identical sequences at the ends of RNA segments of both types of influenza viruses indicates that they have been specifically conserved during evolution.     

Replication of poly dA and poly rA by a Drosophila DNA polymerase

The activity of a 7.3S-8.3S Drosophila DNA polymerase was characterized in detail using poly dA.p(dT)[unk] and poly rA.p(dT)[unk]. With poly dA.p(dT)[unk], Mg(2+) ion was the preferred divalent cation, and enzyme activity was inhibited by K(+) ion and by spermidine. With poly rA.p(dT)[unk], Mn(2+) ion was the preferred divalent cation and enzyme activity was stimulated by K(+) ion and by spermidine. The dependence of enzyme activity on the concentration of primer-template and on the ratio of primer to template was the same in both reactions. The two enzyme activities were identically inhibited by N-ethylmaleimide. Poly dA was replicated extensively and poly rA was replicated partially. The activation energy for poly dA replication was twice that for poly rA replication. Enzyme activity with poly dA.p(dT)[unk] was more stable to thermal inactivation than was enzyme activity with poly rA.p(dT)[unk]. These studies suggest that the same enzyme responds to both the deoxy- and the ribohomopolymer template but that the mechanisms of replication may be different.     

Rep-PCR of tropical rhizobia for strain fingerprinting, biodiversity appraisal and as a taxonomic and phylogenetic tool

With more than 30 million doses of rhizobial inoculants marketed per year, it is probable that Brazilian agriculture benefits more than any other country from symbiotic N₂ fixation. As a result of strain-selection programs, 142 strains of rhizobia are officially recommended for use in commercial inoculants for ninety-six leguminous crops. In this study, sixty-eight of these elite strains were characterized by rep-PCR with the BOX-primer. Reproducibility of the DNA profiles was confirmed, suggesting efficacy of BOX-PCR both for control of quality of inoculants and for preliminary characterization of rhizobial culture collections. Strains of different species never showed similarity higher than 70% in the BOX-PCR analysis, however, some strains of the same species fit into more than one cluster, and correlation between BOX-PCR products and l6S rRNA sequences was low (7.6%). On the other hand, a polyphasic approach — 20%∶80% of BOX-PCR:16S rRNA which correlated well with the l6S rRNA analysis (95%), and provided higher definition of the genotypes, resulting in clearer indications of the taxonomic groups — might expedite rhizobial diversity studies.     

Docosahexaenoic acid is selectively enriched in plasma phospholipids during pregnancy in Trinidadian women--results of a pilot study

The fetal demand for docosahexaenoic acid (DHA) has to be satisfied by the mother. We determined the fatty acids in maternal plasma non-esterified fatty acid (NEFA), triacylglycerol (TAG) and phosphatidylcholine (PC), in a cross-sectional study of non-pregnant (n = 10), pregnant (n = 19), and postpartum (n = 9) women. There were lipid class-dependent differences in plasma polyunsaturated fatty acid (PUFA) concentrations between groups. During pregnancy, DHA was most highly enriched in PC, about 230%, with more modest enrichment for linoleic acid (LA) and arachidonic acid (AA), and no enrichment of alpha-linolenic acid (alpha-LNA). There was relative enrichment of LA, AA and alpha-LNA in TAG, but not of DHA. There was no specific enrichment of any PUFA in the NEFA pool. These data accord with the suggestion that the enrichment of alpha-LNA in TAG and of DHA in phospholipids reflects hepatic regulation of n-3 PUFA metabolism which potentially enhances the delivery of DHA to the placenta.     

Complexity of the heat-soluble LEA proteome in Artemia species

The brine shrimp Artemia is a well known stress tolerant invertebrate found on most continents. Under certain conditions females produce cysts (encysted gastrulae) that enter diapause, a state of obligate dormancy. During developmental formation of diapause embryos several different types of stress proteins accumulate in large amounts, including the late embryogenesis abundant (LEA) proteins. In this study we used a combination of heterologous group 3 LEA antibodies to demonstrate that the heat-soluble proteome of the cysts contains up to 12 distinct putative group 3 LEA proteins that complement the group 1 LEA proteins found previously. Most antibody-positive, heat-soluble proteins were larger than 50 kDa although antibody positive proteins of 20–38 kDa were also detected. Both nuclei and mitochondria had distinct complements of the putative group 3 LEA proteins. A few small group 3 LEA proteins were induced by cycles of hydration–dehydration along with one protein of about 62 kDa. The expression of group 3 LEA proteins, unlike members of group 1, was not restricted to encysted diapause embryos. Three to five putative group 3 LEA proteins were expressed in gravid females and in larvae. Cysts of different species from various geographic locations had distinct complements of group 3 LEA proteins suggesting rapid evolution of the LEA proteins or differences in the type of group 3 Lea genes expressed. Our results demonstrate the potential importance of group 3 LEA proteins in embryos and other life cycle stages of this animal extremophile.     

The effect of high-load vs. high-repetition training on endurance performance

The purpose of this study was to compare the effects of high-load (H-load) periodized resistance training and high-repetition (H-rep) reverse step loading periodized resistance training on endurance performance. Twenty-six female university rowers (age = 20 +/- 1 year) were randomly assigned to H-load (5 novice, 8 varsity) or H-rep (7 novice, 6 varsity) groups. Subjects were pre- and posttested using a 2,000-m rowing ergometer test. Outcome variables included VO2 peak, time to test completion, total power, average power per stroke, total number of strokes, stroke rate, and body mass. Subjects trained for 8 weeks using identical exercises. Varsity rowers who performed H-load training demonstrated greater improvement compared with those who performed H-rep training. Novice rowers who performed H-rep training demonstrated greater improvement compared with those who performed H-load training. High-load periodized training appears to be more effective for athletes with advanced training status, and H-rep reverse step loading periodized training is more effective for those who are relatively untrained.