Timing, location and crop species influence the magnitude of amelioration of aluminum toxicity by magnesium

The protective effect of cations, especially Ca and Mg, against aluminum (Al) rhizotoxicity has been extensively investigated in the last decades. The mechanisms by which the process occurs are however only beginning to be elucidated. Six experiments were carried out here to characterize the protective effect of Mg application in relation to timing, location and crop specificity: Experiment 1 - Protective effect of Mg compared to Ca; Experiment 2 - Protective effect of Mg on distinct root classes of 15 soybean genotypes; Experiment 3 - Effect of timing of Mg supply on the response of soybean cvs. to Al; Experiment 4 - Investigating whether the Mg protective effect is apoplastic or simplastic using a split-root system; Experiment 5 - Protective effect of Mg supplied in solution or foliar spraying, and Experiment 6 - Protective effect of Mg on Al rhizotoxicity in other crops. It was found that the addition of 50 mmol L-1 Mg to solutions containing toxic Al increased Al tolerance in 15 soybean cultivars. This caused soybean cultivars known as Al-sensitive to behave as if they were tolerant. The protective action of Mg seems to require constant Mg supply in the external medium. Supplying Mg up to 6 h after root exposition to Al was sufficient to maintain normal soybean root growth, but root growth was not recovered by Mg addition 12 h after Al treatments. Mg application to half of the root system not exposed to Al was not sufficient to prevent Al toxicity on the other half exposed to Al without Mg in rooting medium, indicating the existence of an external protection mechanism of Mg. Foliar spraying with Mg also failed to decrease Al toxicity, indicating a possible apoplastic role of Mg. The protective effect of Mg appeared to be soybean-specific since Mg supply did not substantially improve root elongation in sorghum, wheat, corn, cotton, rice, or snap bean when grown in the presence of toxic Al concentrations.

Implicações da origem das linhagens de feijoeiro na magnitude da interação com ambientes

O objetivo deste trabalho foi verificar as implicações da origem de linhagens de feijão na magnitude da interação com ambientes e os fatores ambientais que mais contribuem para esta interação. Foram utilizados dados dos experimentos de valor de cultivo e uso, conduzidos em Lavras e Viçosa, MG, nos biênios 2002/2003, 2005/2006 e 2007/2008, nas safras de cultivo das águas, seca e inverno. Foram avaliadas linhagens da Universidade Federal de Lavras, da Universidade Federal de Viçosa e da Embrapa. Os dados de produtividade de grãos foram submetidos a análises de variância por ambiente e análises conjuntas por biênio, para cada local e para os dois locais em conjunto. Foram estimados os coeficientes de determinação de cada fonte de variação, e foram realizadas análises de estabilidade por meio das estimativas de ecovalência. As interações que envolveram as linhagens tiveram pequena participação na variação total nos três biênios. Apesar de ter havido significância das interações genótipo x local quanto à variação total, sua magnitude não foi expressiva. O local de origem não influencia a estabilidade das linhagens quando as suas condições ambientais são semelhantes às do local de cultivo, mas interfere no desempenho das linhagens quando as condições ambientais são muito diferentes.

Determinação em tempo real da magnitude de danos físicos por impacto em linhas de beneficiamento e em condições de laboratório e seus efeitos na qualidade de tomate

O tomate de mesa é uma das principais hortaliças consumidas no Brasil e apresenta elevados índices de perdas pós-colheita. O objetivo deste trabalho foi avaliar a magnitude dos impactos verificados em linhas de beneficiamento para tomate de mesa, bem como determinar, em laboratório, as alterações na qualidade de tomates submetidos a danos físicos controlados em diferentes superfícies. Para a avaliação dos pontos críticos e registro da magnitude dos impactos, foi usada uma esfera instrumentada. Os pontos críticos de transferência demonstraram valores de aceleração entre 30 e 129 G (m s-2). Os testes laboratoriais evidenciaram que superfícies acolchoadas reduziram em até 31% a magnitude de impacto. A incidência de danos físicos internos foi crescente e atingiu 79% em superfícies rígidas para a maior altura de queda livre. Por outro lado, observou-se redução na incidência de danos físicos nos frutos quando superfícies protetoras foram utilizadas, verificando-se na altura de 10 cm um limite mínimo de 5% de danos severos, enquanto para superfície rígida o mínimo correspondeu a 10%. As variáveis de qualidade foram alteradas, verificando-se maior perda de massa, maiores valores de acidez total, menores valores de ácido ascórbico e sólidos solúveis para maiores alturas de queda livre sobre superfícies rígidas.

The effect of an aerobic training program on the electrical remodeling of the heart: high-frequency components of the signal-averaged electrocardiogram are predictors of the maximal aerobic power

Increased heart rate variability (HRV) and high-frequency content of the terminal region of the ventricular activation of signal-averaged ECG (SAECG) have been reported in athletes. The present study investigates HRV and SAECG parameters as predictors of maximal aerobic power (VO2max) in athletes. HRV, SAECG and VO2max were determined in 18 high-performance long-distance (25 ± 6 years; 17 males) runners 24 h after a training session. Clinical visits, ECG and VO2max determination were scheduled for all athletes during thew training period. A group of 18 untrained healthy volunteers matched for age, gender, and body surface area was included as controls. SAECG was acquired in the resting supine position for 15 min and processed to extract average RR interval (Mean-RR) and root mean squared standard deviation (RMSSD) of the difference of two consecutive normal RR intervals. SAECG variables analyzed in the vector magnitude with 40-250 Hz band-pass bi-directional filtering were: total and 40-µV terminal (LAS40) duration of ventricular activation, RMS voltage of total (RMST) and of the 40-ms terminal region of ventricular activation. Linear and multivariate stepwise logistic regressions oriented by inter-group comparisons were adjusted in significant variables in order to predict VO2max, with a P < 0.05 considered to be significant. VO2max correlated significantly (P < 0.05) with RMST (r = 0.77), Mean-RR (r = 0.62), RMSSD (r = 0.47), and LAS40 (r = -0.39). RMST was the independent predictor of VO2max. In athletes, HRV and high-frequency components of the SAECG correlate with VO2max and the high-frequency content of SAECG is an independent predictor of VO2max.

Increased coherence among striatal regions in the theta range during attentive wakefulness

The striatum, the largest component of the basal ganglia, is usually subdivided into associative, motor and limbic components. However, the electrophysiological interactions between these three subsystems during behavior remain largely unknown. We hypothesized that the striatum might be particularly active during exploratory behavior, which is presumably associated with increased attention. We investigated the modulation of local field potentials (LFPs) in the striatum during attentive wakefulness in freely moving rats. To this end, we implanted microelectrodes into different parts of the striatum of Wistar rats, as well as into the motor, associative and limbic cortices. We then used electromyograms to identify motor activity and analyzed the instantaneous frequency, power spectra and partial directed coherence during exploratory behavior. We observed fine modulation in the theta frequency range of striatal LFPs in 92.5 ± 2.5% of all epochs of exploratory behavior. Concomitantly, the theta power spectrum increased in all striatal channels (P < 0.001), and coherence analysis revealed strong connectivity (coefficients >0.7) between the primary motor cortex and the rostral part of the caudatoputamen nucleus, as well as among all striatal channels (P < 0.001). Conclusively, we observed a pattern of strong theta band activation in the entire striatum during attentive wakefulness, as well as a strong coherence between the motor cortex and the entire striatum. We suggest that this activation reflects the integration of motor, cognitive and limbic systems during attentive wakefulness.

Optical coherence tomography imaging of the basal ganglia: feasibility and brief review

Optical coherence tomography (OCT) is a promising medical imaging technique that uses light to capture real-time cross-sectional images from biological tissues in micrometer resolution. Commercially available optical coherence tomography systems are employed in diverse applications, including art conservation and diagnostic medicine, notably in cardiology and ophthalmology. Application of this technology in the brain may enable distinction between white matter and gray matter, and obtainment of detailed images from within the encephalon. We present, herein, the in vivo implementation of OCT imaging in the rat brain striatum. For this, two male 60-day-old rats (Rattus norvegicus, Albinus variation, Wistar) were stereotactically implanted with guide cannulas into the striatum to guide a 2.7-French diameter high-definition OCT imaging catheter (Dragonfly™, St. Jude Medical, USA). Obtained images were compared with corresponding histologically stained sections to collect imaging samples. A brief analysis of OCT technology and its current applications is also reported, as well as intra-cerebral OCT feasibility on brain mapping during neurosurgical procedures.