Periphyton on natural substratum in jurumirim reservoir (São Paulo, Brazil): Community biomass and primary productivity

Seasonal variation in the biomass and primary productivity of the periphyton on natural substratum (internodes of Echiiwchloa polystaclya HBK Hitch.) was studied during one year (from August 1993 to July 1994) in a lagoon with permanent connection with a river. We also analysed the relationships between the hydrological regime, climatic conditions and physico-chemical variables of water with the biological compounds of the periphyton. Values of dry mass, ash-free dry mass, chlorophyll a and phaeophytin of periphyton ranged from 0.55±0.24 g m-2 to 7.86±4.93 g m-2; 0.28±0.18 g m-2 to 3.72±2.23 g m-2; 0.57±0.09 mg m-2 to 15.57±4.52 mg m-2; 0.03±0.03 mg m-2 to 4.74±3.46 mg m-2, respectively. The primary productivity of periphytic algae measured by C14 method ranged from 6.45±1.29 mg C m-2 h-1 to 52.88± 7.55 mg C m-2 h-1. The biomass showed a peak in October 1993, February and April 1994. Higher value of primary productivity was recorded in December 1993 and January 1994 and was due to the peculiar light and nutrition conditions during this period. We conclude that biomass and productivity of the community are controlled mainly by hydrological regime (fluctuations of water level). © INTERNATIONAL SCIENTIFIC PUBLICATIONS.

Taxonomy and distribution of Paralemanea (Lemaneaceae, Rhodophyta) in Central Mexico

Three collections of Paralemanea from Central Mexico included two species. Paralemanea mexicana is large (length ≥ 4.0 cm; diameter > 400 μm) and generally branched (≥ 40 % of plants branched), with whorled branches, of first to second order. Paralemanea annulata is small (length < 5.0 cm ; diameter < 500 μm), generally unbranched (≤ 5 % of plants branched), with branches of first order. Spermatangial sori contained obovoid spermatangia, formed from cells of the outer cortical layers, extending above the thallus surface. Carpogonial branches are described for the first time in P. mexicana. They develop on lateral filaments at nodes or internodes and have ovoid to globular cells, abundantly branched at the basal portion, penetrating the cortex towards the thallus surface. Carposporophytes are sessile on the inner portion of the cortex and produce carpospores in chains of up to twelve. The 'Chantransia' stage was observed in P. mexicana. Paralemanea annulata is described for the first time from Mexico and P. mexicana is endemic from this country. Both species were collected in cold (temperature 12-16°C), acidic (pH 5.5-6.0), shallow (depth 1-60 cm) and moderate to fast flowing waters (> 35 cm s-1), in shaded or partly shaded river segments, on rocky substrata (mostly bedrock).

Molecular model of shikimate kinase from Mycobacterium tuberculosis

Tuberculosis (TB) resurged in the late 1980s and now kills approximately 3 million people a year. The reemergence of tuberculosis as a public health threat has created a need to develop new anti-mycobacterial agents. The shikimate pathway is an attractive target for herbicides and anti-microbial agents development because it is essential in algae, higher plants, bacteria, and fungi, but absent from mammals. Homologs to enzymes in the shikimate pathway have been identified in the genome sequence of Mycobacterium tuberculosis. Among them, the shikimate kinase I encoding gene (aroK) was proposed to be present by sequence homology. Accordingly, to pave the way for structural and functional efforts towards anti-mycobacterial agents development, here we describe the molecular modeling of M. tuberculosis shikimate kinase that should provide a structural framework on which the design of specific inhibitors may be based. © 2002 Elsevier Science (USA). All rights reserved.

Photosynthetic characteristics of charophytes from tropical iotic ecosystems

Responses of photosynthetic rates, determined by oxygen evolution using the light and dark bottles technique, to different temperatures, irradiances, pH, and diurnal rhythm were analyzed under laboratory conditions in four charophyte species (Chara braunii Gmelin, C. guairensis R. Bicudo, Nitella subglomerata A. Braun and Nitella sp.) from Iotic habitats in southeastern Brazil. Parameters derived from the photosynthesis versus irradiance curves indicated affinity to low irradiances for all algae tested. Some degree of photoinhibition, [β = -(0.30-0.13) mg 02 g-1 dry weight h-1 (μmol photons m-2 s-1)-1], low light compensation points (lc = 4-20 μmol photons m-2 s-1) were found for all species analyzed, as well as low values of light saturation parameter (lk) and saturation (ls) 29-130 and 92-169 μmol photons m-2 S-1, respectively. Photoacclimation was observed in two populations of N. subglomerata collected from sites with different irradiances, consisting of variations in photosynthetic parameters (higher values of α, and lower of lk and maximum photosynthetic rate, Pmax, in the population under lower irradiance). The highest photosynthetic rates for Chara species were observed at 10-15°C, while for Nitella the highest photosynthetic rate was observed at 20-25°C, despite the lack of significant differences among most levels tested. Rates of dark respiration significantly increase with temperature, with the highest values at 25°C. The results from pH experiments showed highest photosynthetic rates under pH 4.0 for all algae, suggesting higher affinity for inorganic carbon in the form of carbon dioxide, except in one population of N. subglomerata, with similar rates under the three levels, suggesting indistinct use of bicarbonate and carbon dioxide. Diurnal changes in photosynthetic rates revealed a general pattern for most algae tested, which was characterized by two peaks: the first (higher) during the morning (07.00-11.00) and the second (lower) in the afternoon (14.00-17.00). This suggests an endogenous rhythm determining the daily variations in photosynthetic rates.