Scielo RSS <![CDATA[Brazilian Journal of Botany]]> vol. 35 num. 4 lang. pt <![CDATA[SciELO Logo]]> <![CDATA[<b>Announcement</b>]]> <![CDATA[Editorial]]> <![CDATA[<b>An overview of lignin metabolism and its effect on biomass recalcitrance</b>]]> Lignin, after cellulose, is the second most abundant biopolymer on Earth, accounting for 30% of the organic carbon in the biosphere. It is considered an important evolutionary adaptation of plants during their transition from the aquatic environment to land, since it bestowed the early tracheophytes with physical support to stand upright and enabled long-distance transport of water and solutes by waterproofing the vascular tissue. Although essential for plant growth and development, lignin is the major plant cell wall component responsible for biomass recalcitrance to industrial processing. The fact that lignin is a non-linear aromatic polymer built with chemically diverse and poorly reactive linkages and a variety of monomer units precludes the ability of any single enzyme to properly recognize and degrade it. Consequently, the use of lignocellulosic feedstock as a renewable and sustainable resource for the production of biofuels and bio-based materials will depend on the identification and characterization of the factors that determine plant biomass recalcitrance, especially the highly complex phenolic polymer lignin. Here, we summarize the current knowledge regarding lignin metabolism in plants, its effect on biomass recalcitrance and the emergent strategies to modify biomass recalcitrance through metabolic engineering of the lignin pathway. In addition, the potential use of sugarcane as a second-generation biofuel crop and the advances in lignin-related studies in sugarcane are discussed. <![CDATA[<b>Floristic surveys of aquatic macrophytes in reservoirs in the Agreste zone of Pernambuco State, Brazil</b>]]> We surveyed the aquatic macrophytes in reservoirs in Camocim de São Félix in the Agreste zone of Pernambuco State, Brazil. Plants were collected on a bimonthly schedule from November/2008 to May/2009 in four reservoirs, and 33 taxa distributed among 23 families were encountered. The family Cyperaceae had the greatest number of species, followed by Lemnaceae. The predominant biologic form was emergent (33.3%) reflecting the extensive shorelines around the reservoirs analyzed. <![CDATA[<b>A new species of <i>Lemmermanniella</i> (Cyanobacteria) from the Atlantic Rainforest, Brazil</b>]]> The Brazilian Atlantic Rainforest is a highly heterogeneous ecosystem comprising large numbers of tropical and subtropical habitats favorable to the development of cyanobacteria. Studies on cyanobacteria in this ecosystem are still rare, however, especially those involving unicellular and colonial types. The high biodiversity and endemism of this biome has been extremely impacted and fragmented, and less than 10% of its original vegetation cover remains today. We describe here a new species of a colonial cyanobacteria, Lemmermanniella terrestris, found on dry soils in a subtropical region of the Atlantic Rainforest in the municipality of Cananéia in southern São Paulo State, Brazil. This new taxon demonstrated all of the diacritical features of the genus Lemmermanniella but, unlike the other species of the genus, it was growing on the soil surface and not in an aquatic environment. A set of morphological features, including colonies composed of subcolonies, and cell dimensions, shapes and contents distinguish it from other species of the genus. Considering that species of Lemmermanniella are found in very distinct habitats (such as thermal and brackish waters) and that they maintain the same life cycle described for the genus in all of those environments, the morphological structures of the colonies can be used as reliable markers for identifying the genus, and its species differ primarily in relation to the habitats they occupy. <![CDATA[<b>Cyanobacteria from coastal lagoons in southern Brazil</b>: <b>non-heterocytous filamentous organisms</b>]]> This study describes and illustrates non-heterocytous filamentous cyanobacteria found in lagoon systems on the coastal plains of Rio Grande do Sul State. Collections were carried out in different freshwater bodies along the eastern (Casamento Lake area) and western (Tapes City area) margins of the Patos Lagoon (UTM 461948-6595095 and 542910-6645535) using a plankton net (25 µm mesh) in pelagic and littoral zones as well as by squeezing submerged parts of aquatic macrophytes, during both the rainy and dry seasons, from May to December/2003. Twenty two species belonging to the families Phormidiaceae (eight taxa), Pseudanabaenaceae (seven taxa), Oscillatoriaceae (six taxa), and Spirulinaceae (one taxon) were identified. Among these species, five are reported for the first time from Rio Grande do Sul State: Leptolyngbya cebennensis, Microcoleus subtorulosus, Oscillatoria cf. anguina, O. curviceps and Phormidium formosum. <![CDATA[<b>Relationships between crown architecture and available irradiance in two <i>cerrado</i> species with different leaf phenologies</b>]]> Structural differences between cerrado species with different leaf phenologies are linked to crown architecture, leaf production, and biomass allocation to shoots and leaves. The present study characterized crown structures and the patterns of biomass allocation to leaves and shoots in two woody cerrado species with contrasting leaf phenologies and quantified the irradiance reaching their leaves to determine the best period during the day for photosynthetic activity. The shoots and leaves of five individuals of both Annona coriacea (deciduous) and Hymenaea stigonocarpa (evergreen) were collected along a 50 m transect in a cerrado fragment within the urban perimeter of Catalão - GO, to determine their patterns of biomass allocation in their crowns. The evergreen H. stigonocarpa had significantly higher mean values of shoot inclination (SI), petiole length (PL), leaf area (LA), leaf display index (LDI), and individual leaf area per shoot (ILA), while the deciduous species A. coriacea had significantly higher leaf numbers (LN). The more complex crown of H. stigonocarpa had shoots in more erect positions (orthotropic), with intense self-shading within shoots; A. coriacea, on the other hand, had slanting (plagiotropic) shoots in the crown, allowing similar irradiance levels to all leaf surfaces. The production of plagiotropic shoots by the deciduous species (A. coriacea) is a strategy that enables its use of incident sunlight early in the morning and preventing excessive water loss or excessive irradiance. Hymenaea stigonocarpa (an evergreen), by contrast, had orthotropic shoots and uses intense self-shading as a strategy to avoid excessive irradiance, especially at midday. Differences in crown architectures between evergreen and deciduous species of cerrado sensu stricto can therefore be viewed as adaptations to the environmental light regime. <![CDATA[<b>Diurnal changes in storage carbohydrate metabolism in cotyledons of the tropical tree <i>Hymenaea courbaril</i> L. (Leguminosae)</b>]]> The cotyledons of Hymenaea courbaril store large amounts of xyloglucan, a cell wall polysaccharide that is believed to serve as storage for the period of seedling establishment. During storage mobilisation, xyloglucan seems to be degraded by a continuous process that starts right after radicle protrusion and follows up to the establishment of photosynthesis. Here we show evidence that events related to the hydrolases activities and production (α-xylosidase, β-galactosidase, β-glucosidase and xyloglucan endo-β-transglucosilase) as well as auxin, showed changes that follow the diurnal cycle. The period of higher hydrolases activities was between 6pm and 6am, which is out of phase with photosynthesis. Among the enzymes, α-xilosidase seems to be more important than β-glucosidase and β-galactosidase in the xyloglucan disassembling mechanism. Likewise, the sugars related with sucrose metabolism followed the rhythm of the hydrolases, but starch levels were shown to be practically constant. A high level of auxin was observed during the night, what is compatible with the hypothesis that this hormone would be one of the regulators of the whole process. The probable biological meaning of the existence of such a complex control mechanism during storage mobilisation is likely to be related to a remarkably high level of efficiency of carbon usage by the growing seedling of Hymenaea courbaril, allowing the establishment of very vigorous seedlings in the tropical forest. <![CDATA[<b>Influence of air temperature on proteinase activity and beverage quality in <i>Coffea arabica</i></b>]]> Fruits were collected from trees of Coffea arabica cv. Obatã grown at Mococa and Adamantina in São Paulo State, Brazil, which are regions with marked differences in air temperature that produce coffee with distinct qualities. Mococa is a cooler location that produces high-quality coffee, whereas coffee from Adamantina is of lower quality. The amino acid and protein contents, amino acid profile, and proteinase activity and type in endosperm protein extracts were analysed. Proteinase genes were identified, and their expression was assayed. All results indicate that temperature plays a role in controlling proteinase activity in coffee endosperm. Proteinase activity was higher in the endosperm of immature fruits from Adamantina, which was correlated with higher amino acid content, changes in the amino acid profile, and increased gene expression. Cysteine proteinases were the main class of proteinases in the protein extracts. These data suggest that temperature plays an important role in coffee quality by altering nitrogen compound composition. <![CDATA[<b>Modeling temporal variations of <i>Gracilaria</i> Greville and <i>Hypnea</i> J.V. Lamouroux (Rhodophyta) assemblages on a midlittoral reef platform at Piedade Beach, Pernambuco State, Brazil</b>]]> The diversity of algal banks composed of species out the genera Gracilaria Greville and Hypnea J.V. Lamouroux have been impacted by commercial exploitation and coastal eutrophication. The present study sought to construct dynamic models based on algal physiology to simulate seasonal variations in the biomasses of Gracilaria and Hypnea an intertidal reef at Piedade Beach in Jaboatão dos Guararapes, Pernambuco State, Brazil. Five 20 × 20 cm plots in a reef pool on a midlittoral reef platform were randomly sampled during April, June, August, October, and December/2009 and in January and March/2010. Water temperature, pH, irradiance, oxygen and salinity levels as well as the concentrations of ammonia, nitrate and phosphate were measured at the sampling site. Forcing functions were employed in the model to represent abiotic factors, and algal decay was simulated with a dispersal function. Algal growth was modeled using a logistic function and was found to be sensitive to temperature and salinity. Maximum absorption rates of ammonia and phosphate were higher in Hypnea than in Gracilaria, indicating that the former takes up nutrients more efficiently at higher concentrations. Gracilaria biomass peaked at approximately 120 g (dry weight m-2) in March/2010 and was significantly lower in August/2009; Hypnea biomasses, on the other hand, did not show any significant variations among the different months, indicating that resource competition may influence the productivity of these algae. <![CDATA[<b>Floristic composition of a conservation area in the Federal District of Brazil</b>]]> Cerradão vegetation shares many species with savanna and forest areas and is one of the most vulnerable phytophysiognomies in the Cerrado (Brazilian savanna) biome. The floristic composition of the Cerradão Biological Reserve was examined between September/2007 and November/2008. A total of 282 species distributed among 194 genera and 75 families were encountered, demonstrating proportions of 0.91 herbaceous species and 0.54 shrub species for each tree species. Fabaceae, Asteraceae, Rubiaceae, Poaceae, Myrtaceae, Malpighiaceae, and Melastomataceae were the most species-rich families. Fully 72.3% of the species of this dystrophic cerradão were shared by cerrado and forest vegetations, while 60.43% were shared by other cerradão sites, although the largest proportion of species (91%) were shared with cerrado sensu stricto. No species was found to be exclusive to this cerradão site, but approximately 95% of all species were native to the Cerrado biome. <![CDATA[<b>Viability and vigor of jamun (<i>Syzygium cumini</i>) seeds</b>]]> Jamun (Syzygium cumini L. Skeels) (Black plum, Damson plum) fruits weigh between 2-5 g at maturity. Fresh seeds represented 20-80% of the total fruit weight; the seed coat and cotyledons contributed 6% and 94% to the total seed weight respectively, while the weight of the embryonic axis was insignificant. Only the embryonic axis stained with Tetrazolium, not the cotyledons. The seeds are polyembryonic with up to four embryos, of which at most three germinate. Decoated seeds germinated faster than coated seeds under nursery conditions, with high significant germination percentages, dry matter production rates and vigor indices. The lack of staining of the cotyledon by tetrazolium was probably due to the presence of an impermeable layer. Decoating seeds for faster germination is recommended. <![CDATA[<b>Isothermal seed germination of <i>Adenanthera pavonina</i></b>]]> This work reports aspects of seed germination at different temperatures of Adenanthera pavonina L., a woody Southeast Asian Leguminosae. Germination was studied by measuring the final percentages, the rate, the rate variance and the synchronisation of the individual seeds calculated by the minimal informational entropy of frequencies distribution of seed germination. Overlapping the germinability range with the range for the highest values of germination rates and the minimal informational entropy of frequencies distribution of seed germination, we found that the best temperature for the germination of A. pavonina seeds is 35 ºC. The slope µ of the Arrhenius plot of the germination rates is positive for T < 35 ºC and negative for T &gt; 35 ºC. The activation enthalpies, estimated from closely-spaced points, shows that |ΔH-| < 12 Cal mol-1 occur for temperatures in the range between 25 ºC and 40 ºC. The ecological implication of these results are that this species may germinate very fast in tropical areas during the summer season. This may be an advantage to the establishment of this species under the climatic conditions in those areas.