Ecophysiology of selected tree species in different plant communities at the periphery of the Atlantic Forest of SE—Brazil III. Three legume trees in a semi-deciduous dry forest

Three legume tree species (Fabaceae) occurring abundantly in a semi-deciduous tropical dry forest of the Atlantic forest complex in southeastern Brazil were subjected to a comparative ecophysiological study at the end of the dry season/beginning of the wet season. The trees chosen were morphologically very similar: Caesalpinia echinata Lam. and Caesalpinia ferrea Mart. ex. Tul., both 10–20 m of height, of the sub-family Caesalpinioideae, and the somewhat smaller, 2–4 m tall, Machaerium obovatum Kuhlm. & Hoehne of the sub-family Faboideae. Despite their similarities with respect to their geographic distribution restricted to Brazilian dry forests, their comparable abundance in the study site and their phylogenetic proximity, the three species display distinctly different ecophysiological behaviour. Compared to the other two species, C. ferrea had the highest photosynthetic capacity (maximum apparent photosynthetic electron transport rate, ETR_max) and higher saturation light-intensity, was less subject to photoinhibition as indicated by potential quantum yield of photosystem II (F _v/F _m) and had the lowest bulk N content of which soluble non-protein N compounds were only 1.5%. It showed stronger sun plant characteristics. C. echinata had lower photosynthetic capacity, was under chronic photoinhibition and had high bulk N content of which 6.1% were soluble N compounds with high concentrations of proline. In addition to proline, high concentrations of sugars may serve as osmoprotectants. M. obovatum also showed lower photosynthetic capacity and was under chronic photoinhibition. Here, arginine may have a function as osmoprotectant. The ecophysiological differences between the three species are not related to local abundance. However, the observations presented highlight a contrasting behaviour of the otherwise very similar compatriot species.     

Levels of DNA damage in blood leukocyte samples from non-diabetic and diabetic female rats and their fetuses exposed to air or cigarette smoke

The objective of the present study was to evaluate DNA damage level in blood leukocytes from diabetic and non-diabetic female Wistar rats exposed to air or to cigarette smoke, and to correlate the findings with levels of DNA damage detected in blood leukocyte samples from their fetuses. A total of 20 rats were distributed into four experimental groups: non-diabetic (control; G1) and diabetic exposed to filtered air (G2); non-diabetic (G3) and diabetic (G4) exposed to cigarette smoke. Rats placed into whole-body exposure chambers were exposed for 30min to filtered air (control) or to tobacco smoke generated from 10 cigarettes, twice a day, for 2 months. Diabetes was induced by a pancreatic beta-cytotoxic agent, streptozotocin (40mg/kgb.w.). At day 21 of pregnancy, each rat was anesthetized and humanely killed to obtain maternal and fetal blood samples for genotoxicity analysis using the alkaline comet assay. G2, G3 and G4 dams presented higher DNA damage values in tail moment and tail length as compared to G1 group. There was a significant positive correlation between DNA damage levels in blood leukocyte samples from G2 and G3 groups (tail moment); G3 and G4 groups (tail length) and G3 group (tail intensity) and their fetuses. Thus, this study showed the association of severe diabetes and tobacco cigarette smoke exposure did not exacerbate levels of maternal and fetal DNA damages related with only diabetes or cigarette smoke exposure. Based on the results obtained and taking into account other published data, maternal diabetes requires rigid clinical control and public health and education campaigns should be increased to encourage individuals, especially pregnant women, to stop smoking.     

Guanidinoacetate Decreases Antioxidant Defenses and Total Protein Sulfhydryl Content in Striatum of Rats

Guanidinoacetate methyltransferase (GAMT) deficiency is an inherited neurometabolic disorder biochemically characterized by tissue accumulation of guanidinoacetate (GAA) and depletion of creatine. Affected patients present epilepsy and mental retardation whose pathogeny is unclear. In the present study we investigated the in vitro and in vivo (intrastriatal administration) effects of GAA on some oxidative stress parameters in rat striatum. Sixty-day-old rats were used for intrastriatal infusion of GAA. For the in vitro studies, 60-day-old Wistar rats were killed by decapitation and the striatum was pre-incubated for 1 h at 37°C in the presence of GAA at final concentrations ranging from 10 to 100 μM. Parameters of oxidative stress such as total radical-trapping antioxidant potential (TRAP), antioxidant enzymes (SOD, GPx, and CAT), protein carbonyl and thiol contents were measured. DNA damage was also evaluated. Results showed that GAA administration (in vivo studies) or the addition of 100 μM GAA to assays (in vitro studies) significantly decreased TRAP, SOD activity, and total thiol levels in rat striatum. In contrast, this guanidino compound did not alter protein carbonyl content and the activities of CAT and GPx. DNA damage was not found after intrastriatal administration of GAA. The data indicate that the metabolite accumulating in GAMT deficiency decreases antioxidant capacity and total thiol content in the striatum. It is therefore presumed that this pathomechanism may contribute at least in part to the pathophysiology of the brain injury observed in patients affected by GAMT deficiency.     

Minimizing frustration by folding in an aqueous environment

Although life as we know it evolved in an aqueous medium, the properties of water are not completely understood. In this review, we focus on the role of water in guiding protein folding and stability. Specifically, we discuss the mechanisms of protein folding in an aqueous environment, the effects of water on the folding energy landscape as well as the transition state ensemble, and interactions of water with the folded state. We show that water cannot be viewed as a passive solvent, but rather, plays a very active role in the life of a protein.     

Synthesis of cholera toxin B subunit gene: cloning and expression of a functional 6XHis-tagged protein in Escherichia coli

Cholera toxin B subunit (CTB) has been extensively studied as immunogen, adjuvant, and oral tolerance inductor depending on the antigen conjugated or coadministered. It has been already expressed in several bacterial and yeast systems. In this study, we synthesized a versatile gene coding a 6XHis-tagged CTB (359 bp). The sequence was designed according to codon usage of Escherichia coli, Lactobacillus casei, and Salmonella typhimurium. The gene assembly was based on a polymerase chain reaction, in which the polymerase extends DNA fragments from a pool of overlapping oligonucleotides. The synthetic gene was amplified, cloned, and expressed in E. coli in an insoluble form, reaching levels about 13 mg of purified active pentameric rCTB per liter of induced culture. Western blot and ELISA analyses showed that recombinant CTB is strongly and specifically recognized by polyclonal antibodies against the cholera toxin. The ability to form the functional pentamers was observed in cell culture by the inhibition of cholera toxin activity on Y1 adrenal cells in the presence of recombinant CTB. The 6XHis-tagged CTB provides a simple way to obtain functional CTB through Ni²⁺-charged resin after refolding and also free of possible CTA contaminants as in the case of CTB obtained from Vibrio cholerae cultures.     

Physiological synecology of tree species in relation to geographic distribution and ecophysiological parameters at the Atlantic forest periphery in Brazil: an overview

This paper provides a synthesis of the three papers published in the series Ecophysiology of selected tree species in different plant communities at the periphery of the Atlantic forest of SE – Brazil (Trees, this issue). We reviewed data obtained for seven tree species, belonging to the legume family and the genus Clusia of the Clusiaceae. These groups were chosen because legumes are the most abundant tree species in the Atlantic forest complex (except in the open restingas), and the genus Clusia is reportedly of utmost ecological importance as nurse plants in several habitats of the complex. These species were surveyed along one or more of several forest and open habitats at the margin of the Atlantic rain forest (open restingas, restinga dry forest, inselberg, semideciduous dry forest) and indicated the following general patterns: (1) at the intraspecific level, ecophysiological performance often (but not always) varied largely in both time and space; (2) at the interspecific level, ecophysiological performance was often (but not always) related positively to species dominance in the community; and (3) at both levels, ecophysiological performance was not related to the geographic distribution patterns, i.e., generalists and specialists did not form groups of similarly behaving plants in regard to ecophysiology. We discuss the implications of these findings, compare them with earlier studies, and suggest that ecophysiological research in the Atlantic rain forest complex could enhance its explanatory power by increasing spatial and temporal scales of observation.     

Ecophysiology of selected tree species in different plant communities at the periphery of the Atlantic Forest of SE-Brazil II. Spatial and ontogenetic dynamics in Andira legalis, a deciduous legume tree

Andira legalis Vell. Toledo (Leguminosae, Papilionoideae) is a deciduous tree of the coastal vegetation of Brazil. It was studied in the restinga ecosystems of the Atlantic coast along a moisture gradient of open dry restinga (annual precipitation 800 mm, water table high at 0.9–1.2 m but partially saline), intermediate restinga (annual precipitation 1164 mm, water table low at 2–3 m) and wet restinga (annual precipitation 1000 mm, water table high at 0.5–1 m). In addition, a comparison of the ecophysiological performance was made of A. legalis in the wet restinga and a dune forest (water table low at 2–6 m). Plants of A. legalis at a given site and even within clonal stands show considerable phenological plasticity, where especially timing of leaf shedding and new bud break, leaf expansion and maturation varies between neighbouring individuals and all stages can be observed at the same time. We used analyses of soluble carbohydrate carbon compounds, soluble non-protein nitrogen compounds, stable isotope signatures (¹³C, ¹⁵N) and parameters of fluorescence of chlorophyll a for describing metabolic relations and photosynthetic behaviour and to deduce possible variations in ecophysiological strategies in response to site conditions. The phenological plasticity is described in relation to predominant metabolite levels in leaves, roots, xylem and phloem, but its ecological advantage—perhaps related to staggered resource acquisition and susceptibility to predators—remains an open question. For overall ecophysiological performance among the environmental factors root access to the ground water table appeared to be more essential than significantly different precipitation regimes, as plants in the intermediate restinga appeared to be more stressed than those in the other two open restingas. Shading in the dune forest was also an important environmental constraint.