Characterization of a 3-dehydroquinase gene from Actinobacillus pleuropneumoniae with homology to the eukaryotic genes qa-2 and QUTE

A gene was cloned from Actinobacillus pleuropneumoniae strain 4074 by complementation of an aroD strain of Escherichia coli. The E. coli gene aroD codes for a 3-dehydroquinase enzyme of type I, active in the aromatic biosynthesis pathway. The A. pleuropneumoniae gene, termed aroQ, displays no base or ami no acid sequence homoiogy to aroD of E. coli. It is instead homologous to the QUTE and qa-2 genes, respectively of Aspergillus niduians and Neurospora crassa. These genes code for 3-dehydroquinase enzymes of type ii, involved in the catabolism of quinic acid. The 1.6 kb fragment, which includes aroQ, carries four overlapping or adjacent open reading frames: a dapD gene; aroQ; one without homology to sequences in GenBank; and one with homology to the C-terminal 40% of chlN of E. coli.     

The diversity and distribution of lianas in the Afromontane rain forests of Ethiopia

The diversity and distribution of lianas were studied in five Afromontane rain forests of Ethiopia. Quadrats of 20 × 20 m were laid down along transects in the Bonga, Berhane‐Kontir, Harenna, Yayu and Maji forests. In all forests, 30,917 liana individuals belonging to 123 species in 87 genera and 40 plant families were recorded. The most species‐rich families were Asclepiadaceae (14), Fabaceae (9), Annonaceae (7) and Cucurbitaceae (7). The top 10 dominant families represented 56% of the total number of species. Over 400 other plant species representing different life forms were recorded growing together with lianas. The lianas accounted for over 30% of the total woody plant diversity and over 20% of the total floral diversity in the study areas. The analysis of floristic composition of the forests indicates that the Berhane‐Kontir Forest had the highest Fisher's diversity index α, and Yayu the lowest. Generally, there were low similarities between the forests in terms of species composition. Although lianas were abundant in almost all forests, there was a considerable variation among the forests in terms of density and spatial distribution. The major dispersal modes of lianas were anemochory (30%), mammaliochory (30%), ornithochory and autochory, and the four mechanisms of climbing of lianas were twining (54%), hooking (24%), rooting and use of tendrils. Altitude and human disturbance were found to be important factors affecting liana distribution. The need for sustainable management and use of lianas in the Afromontane rain forests is emphasized.     

Cloning and characterization of the gene encoding the ADP-ribosylation factor in Candida albicans.

We have cloned and sequenced the gene (ARF) encoding the ADP-ribosylation factor (ARF) of Candida albicans. The gene contains an open reading frame of 537 nucleotides (nt) that codes for a protein with an Mr of 20,259. The C. albicans ARF gene is 67-70% identical at the nt level to other ARF sequences including those of humans; the deduced amino acid sequence of C. albicans ARF shows a 78-83% identity and 89-92% similarity to the other ARFs. Southern analysis of C. albicans genomic DNA suggested the presence of a second ARF gene. The presence of multiple ARF genes is a consistent finding among the other organisms previously shown to have ARFs.     

Floristic diversity in fragmented Afromontane rainforests: Altitudinal variation and conservation importance

Question: How does the floristic diversity of Afromontane rainforests change along an altitudinal gradient? What are the implications for conservation planning in these strongly fragmented forest areas that form part of the Eastern Afromontane Biodiversity Hotspot? Location: Bonga, southwestern Ethiopia. Methods: Based on evidence from other montane forests, we hypothesized that altitude has an effect on the floristic diversity of Afromontane rainforests in southwestern Ethiopia. To test this hypothesis, detailed vegetation surveys were carried out in 62 study plots located in four relatively undisturbed forest fragments situated at altitudes between 1600 m and 2300 m. Floristic diversity was evaluated using a combination of multivariate statistical analyses and diversity indices. Results: Ordination and indicator species analyses showed gradual variations in floristic diversity along the altitudinal gradient with a pronounced shift in species composition at ca. 1830 m. Upper montane forest (>1830 m) is characterized by high fern diversity and indicator species that are Afromontane endemics. Lower montane forest (<1830 m) exhibits a greater diversity of tree species and a higher abundance of the flagship species Coffea arabica. Conclusions: Our results provide crucial ecological background information concerning the montane rainforests of Ethiopia, which have been poorly studied until now. We conclude that both forest types identified during this study need to be considered for conservation because of their particular species compositions. Owing to the high degree of forest fragmentation, conservation concepts should consider a multi‐site approach with at least two protected areas at different altitudinal levels.     

Response of secondary vegetation in Eastern Amazonia to relaxed nutrient availability constraints

This study evaluated the effect of nutrient application on the regrowth dynamics of secondary fallow vegetation in an intensely exploited shifting cultivation area in the eastern Amazon region of Brazil. The importance of N, P, K, Ca, Mg, S and a mixture of micronutrients was tested in a minus-one-trial by comparison with a full complement of nutrients and unfertilized control plots. Fertilizers were applied three times during the experiment and their effects were monitored over a period of 2 1/2 years. Prior to the second fertilization, one third of each experimental plot was cleared of the vegetation cover and planted in maize, prior to the third fertilizer application these subplots were planted in sorghum. Biomass of maize and sorghum were used to indicate nutrient constraints and fertilizing effects due to the different treatments. Both crops were limited by P- and N-availability, with greater responses to P. The initial fertilization did not affect the biomass accumulation of the secondary vegetation during the first 15 months, but two additional applications significantly increased biomass in the complete fertilizer treatment compared to the unfertilized control. Biomass accumulation was primarily P-limited, N-limitation was apparent but not significant. The remaining nutrients did not affect plant growth. Fertilization favored production of nutrient-rich leaves. Application of readily available nutrients gave grasses a competitive edge over slower reacting woody vegetation. Fertilization also caused significant shifts in the contribution of woody species to biomass accumulation, as could be demonstrated for two prominent pioneer tree species. Growth response to fertilization as well as the primary limiting nutrient varied among seven dominant species monitored in the secondary vegetation. We conclude that growth of tropical secondary vegetation can be nutrient limited and it might respond significantly to additional nutrients by increasing biomass production.     

Nutrient resources for crop production in the tropics

For the foreseeable future a majority of the population, and almost all the mal- and under-nourished, will continue to be found in the tropics and subtropics. Food security in these parts of the world will have to be met largely from local resources. The productivity of the land is to a large extent determined by the fertlity of the soil, which in turn is mostly determined by its organic matter content and stored nutrients. Soil organic matter is readily lost when organic matter inputs are reduced upon cultivation and more so upon intensification. The concomitant loss of topsoil and possible exposure of subsoil acidity may cause further soil degradation.<br>Plant nutrients to replenish what is yearly taken from the soil to meet the demands for food and fibre amount to 230 million tonnes (Mt). Current fertilizer consumption stands at about 130 Mt of N, P₂O₅,and K₂O, supplemented by an estimated 90 Mt of N from biological nitrogen fixation worldwide. Although 80 per cent of the population lives in the developing world, only half the world''s fertilizer is consumed there. Yet, as much as 50% of the increase in agricultural productivity in the developing world is due to the adoption of fertilizers. World population growth will cause a doubling in these nutrients requirements for the developing world by 2020, which, in the likely case of inadequate production, will need to be met from soil reserves. Because expansion of the cultivable land area is reaching its limits, the reliance on nutrient inputs and their efficient use is bound to grow.<br>With current urban expansion, nutrients in harvested products are increasingly lost from the rural environment as a whole. Estimates of soil nutrient depletion rates for sub-Saharan Africa (SSA) are alarmingly high. The situation may be more favourable in Latin America and Asia where fertilizer inputs are tenfold those of SSA. Closing the nutrient cycle at a community level in rural areas may be tedious; on an inter-regional level it is associated with considerable costs of collection, detoxification and transportation to the farms. Yet, at the rate at which some of the non-renewable resources such as phosphorus and potassium are being exploited, recycling of these nutrients will soon be required. <br>