空气CO2增高条件下荔枝叶片光合作用和超氧自由基产率

研究结果表明,生长在77±5PaCO₂分压下30d的荔枝幼树,其光合速率较大气CO₂分压(39.3Pa)下的低23%,光下线粒体呼吸速率和不包含光下呼吸的CO₂补偿点亦略有降低.空气CO₂增高使叶片最大羧化速率(V_cmax)和最大电子传递速率(J_max)降低,表明大气增高CO₂分压下叶片的光系统I(PSI)能量水平较低,叶片超氧自由基产率亦降低39%,叶片感染荔枝霜疫霉病率则从生长在大气CO₂分压下的1.8%增至9.5%.可能较低光合和呼吸代谢诱致较低的超氧自由基产率,而使叶片易受病害侵染.叶片受病害侵染后表现为超氧自由基的激增.在全球大气CO₂分压增高趋势下须加强对荔枝霜疫霉病的控制.     

Sympathovagal Balance,Nighttime Blood Pressure,and QT Intervals in Normotensive Obese Women

Objective : We describe associations among the heart‐rate‐corrected QT (QTc) interval, QTc dispersion (QTc‐d), circadian BP variation, and autonomic function in obese normotensive women and the effect of sustained weight loss. Research Methods and Procedures : In 71 obese (BMI = 37.14 ± 2.6 kg/m²) women, 25 to 44 years of age, circadian BP variations (24‐hour ambulatory BP monitoring), autonomic function (power spectral analysis of RR interval oscillations), and cardiac repolarization times (QTc‐d and QTc interval) were recorded at baseline and after 1 year of a multidisciplinary program of weight reduction. Results : Compared with nonobese age‐matched women (n = 28, BMI = 23 ± 2.0 kg/m²), obese women had higher values of QTc‐d (p < 0.05) and QTc (p < 0.05), an altered sympathovagal balance (ratio of low‐frequency/high‐frequency power, p < 0.01), and a blunted nocturnal drop in BP (p < 0.01). In obese women, QTc‐d and the QTc interval correlated with diastolic nighttime BP (p < 0.01) and sympathovagal balance (p < 0.01). Waist‐to‐hip ratio, free fatty acids, and plasma insulin levels correlated with QT intervals and reduced nocturnal drops in both systolic and diastolic BP and sympathovagal balance (p < 0.01). After 1 year, obese women lost at least 10% of their original weight, which was associated with decrements of QTc‐d (p < 0.02), the QTc interval (p < 0.05), nighttime BP (p < 0.01), and sympathovagal balance (p < 0.02). Discussion : Sustained weight loss is a safe method to ameliorate diastolic nighttime BP drop and sympathetic overactivity, which may reduce the cardiovascular risk in obese women.     

Effect of Sibutramine on Weight Loss and Blood Pressure: A Meta‐analysis of Controlled Trials

Objective: Sibutramine causes weight loss by suppressing the appetite and by promoting energy expenditure, but it can also increase blood pressure through a norepinephrine effect. The aim of this study was to provide a comprehensive meta‐analysis of randomized, controlled trials on the effects of sibutramine on blood pressure and weight loss. Research Methods and Procedures: Twenty‐one placebo‐controlled, double‐blind, randomized trials of sibutramine were identified using MEDLINE, EMBASE, and a manual search. The effect sizes of sibutramine on weight and systolic (SBP) and diastolic (DBP) blood pressure changes were estimated. Subgroup analyses were undertaken to explore the relationship between effect sizes and the study characteristics. Results: The effect size of sibutramine on weight change was ?1.00 (?1.17 to ?0.84), whereas the effect sizes on SBP and DBP changes were 0.16 (0.08 to 0.24) and 0.26 (0.18 to 0.33), respectively. By subgroup analysis, the effect sizes on weight loss were significantly larger when the dosage was ≥15 mg. The effect sizes on increased SBP were significantly larger when the initial body weight was ≥92 kg and the age was <44 years; similarly, the effect sizes on increased DBP were significantly larger when the initial weight was ≥92 kg. Discussion: Sibutramine showed a large effect on weight loss. Because blood pressure was found to be increased slightly, but significantly, sibutramine should be used cautiously in patients with borderline or high blood pressure. Additional studies on its effect on blood pressure are needed.     

Stabilization of Metals in Subsurface by Biopolymers: Laboratory Drainage Flow Studies

Environmental contamination with heavy metals and radionuclides remains a major problem worldwide. The current clean-up methodologies are based on energy-intensive engineering processes, which are disruptive and costly. A new universal technology targeted for the permanent enclosure and fixation of nuclear and other extreme hazardous metallic wastes in subsurface sites is needed. Such technology will be useful in treating contamination at many sites in the U.S., with specific applications to Department of Energy (DOE) sites. Biopolymers are potential tools for such an innovative technology. Biopolymers have repeated sequences, and therefore provide ample opportunity for chemical reactions with metals, soil particles, and other biopolymers. They also have the additional ability of creating cross-linking interpenetrating networks that can encapsulate the contaminants. Based on this concept, in the present work five biopolymers (xanthan, chitosan, polyhydroxy butyrate, guar gum, polyglutamic acid) were investigated for potential use in the stabilization of metals in the subsurface. The effects of these biopolymers (used alone and in combinations) on soil characteristics (permeability, shear strength) and their metal uptake ability have been studied using laboratory drainage flow systems. Biopolymer solutions were run through the experimental sandpack columns, followed by copper solution and leaching agents (distilled water and hydrochloric acid). The permeability and shear strength of sand were evaluated. Copper uptake capacity of each biopolymer and combination of biopolymers was also studied along with subsequent leaching. All biopolymers tested improved sand characteristics (by decreasing permeability and increasing shear strength) and had good metal uptake ability (60–90%) with relatively low leachability (10–22%). While biopolymers used alone were more efficient in metal uptake, the combination of two biopolymers (xanthan and chitosan) had an increasing plugging effect. These results show the potential of using biopolymers in subsurface metal stabilization.     

超高产水稻剑叶衰老过程中PSⅡ激发压与 Rubisco大、小亚基含量的相关性

研究了大田生长条件下两系超高产杂交水稻(Oryza sati va L.)"两优培九"和我国大面积推广的三系杂交水稻"汕优63"从灌浆期到收获期剑叶PSⅡ光化学特性和Rubjsco大、小亚基含量的变化.结果表明:可溶性蛋白质和叶绿素含量随剑叶生长时间的延长先缓慢下降,后期有一个快速降解的过程,"汕优63"降解的速率高于"两优培九";Fv/Fm和qP都呈下降的趋势,qN则是先降然后上升.激发压(1 qP)在前期的变化较为平稳,后期则急剧增加,"汕优63"较"两优培九"增加快.Rubi Sco大、小亚基的含量与叶绿素、可溶性蛋白含量一样在前期下降比较慢,后期也有一个快速降解的过程,"汕优63"比"两优培九"降解快.激发压的增加与Rubisco大、小亚基的降解呈显著的线性相关性.我们推测PSⅡ激发压的急剧增加可能诱发了水稻剑叶的快速衰老过程."两优培九"高产的重要生理原因之,可能是它比"汕优63"有更强的光合能力并能维持更持久和较高的光合功能期.     

光合作用系统II外周蛋白——P23k去折叠的热力学和动力学

利用荧光光谱学等方法结合高压力技术研究了光合作用系统II中的一个外周蛋白——— 2 3kD(以P2 3k表示 )蛋白的去折叠。热力学研究表明 ,在 2 0℃、180MPa(1MPa =10 .0大气压 )可使该蛋白质完全去折叠 ,而在3℃ ,16 0MPa即可使该蛋白质完全去折叠 ,这是迄今为止有关研究中最易被高压力去折叠的一个蛋白质。在2 0℃ ,该蛋白质在常压下去折叠反应的标准自由能与标准体积变化分别为 2 3.4 5kJ mol和 - 15 0 .3ml mol;动力学研究揭示该蛋白质的折叠反应的活化体积ΔV f 为正值 (84 .1ml mol) ,而去折叠反应的活化体积ΔV u 为负值(- 6 6 .2ml mol)。在常压下 ,折叠和去折叠反应的速度常数 (K0f,K0u)分别为 1.87s- 1 和 1.3× 10 - 4s- 1 ,这些结果为解释该蛋白质易被压力去折叠提供了线索     

Blocking hedgehog signaling after ablation of the dorsal neural tube allows regeneration of the cardiac neural crest and rescue of outflow tract septation

Cardiac neural crest cells (CNCC) migrate into the caudal pharynx and arterial pole of the heart to form the outflow septum. Ablation of the CNCC results in arterial pole malalignment and failure of outflow septation, resulting in a common trunk overriding the right ventricle. Unlike preotic cranial crest, the postotic CNCC do not normally regenerate. We applied the hedgehog signaling inhibitor, cyclopamine (Cyc), to chick embryos after CNCC ablation and found normal heart development at day 9 suggesting that the CNCC population was reconstituted. We ablated the CNCC, and labeled the remaining neural tube with DiI/CSRE and applied cyclopamine. Cells migrated from the neural tube in the CNCC-ablated, cyclopamine-treated embryos but not in untreated CNCC-ablated embryos. The newly generated cells followed the CNCC migration pathways, expressed neural crest markers and supported normal heart development. Finally, we tested whether reducing hedgehog signaling caused redeployment of the dorsal–ventral axis of the injured neural tube, allowing generation of new neural crest-like cells. The dorsal neural tube marker, Pax7, was maintained 12 h after CNCC ablation with Cyc treatment but not in the CNCC-ablated alone. This disruption of dorsal–ventral neural patterning permits a new wave of migratory cardiac neural crest-like cells.     

Morphogenetic movements driving neural tube closure in Xenopus require myosin IIB

Vertebrate neural tube formation involves two distinct morphogenetic events — convergent extension (CE) driven by mediolateral cell intercalation, and bending of the neural plate driven largely by cellular apical constriction. However, the cellular and molecular biomechanics of these processes are not understood. Here, using tissue-targeting techniques, we show that the myosin IIB motor protein complex is essential for both these processes, as well as for conferring resistance to deformation to the neural plate tissue. We show that myosin IIB is required for actin-cytoskeletal organization in both superficial and deep layers of the Xenopus neural plate. In the superficial layer, myosin IIB is needed for apical actin accumulation, which underlies constriction of the neuroepithelial cells, and that ultimately drive neural plate bending, whereas in the deep neural cells myosin IIB organizes a cortical actin cytoskeleton, which we describe for the first time, and that is necessary for both normal neural cell cortical tension and shape and for autonomous CE of the neural tissue. We also show that myosin IIB is required for resistance to deformation (“stiffness”) in the neural plate, indicating that the cytoskeleton-organizing roles of this protein translate in regulation of the biomechanical properties of the neural plate at the tissue-level.     

Incipient forebrain boundaries traced by differential gene expression and fate mapping in the chick neural plate

We correlated available fate maps for the avian neural plate at stages HH4 and HH8 with the progress of local molecular specification, aiming to determine when the molecular specification maps of the primary longitudinal and transversal domains of the anterior forebrain agree with the fate mapped data. To this end, we examined selected gene expression patterns as they normally evolved in whole mounts and sections between HH4 and HH8 (or HH10/11 in some cases), performed novel fate-mapping experiments within the anterior forebrain at HH4 and examined the results at HH8, and correlated grafts with expression of selected gene markers. The data provided new details to the HH4 fate map, and disclosed some genes (e.g., Six3 and Ganf) whose expression domains initially are very extensive and subsequently retract rostralwards. Apart from anteroposterior dynamics, some genes soon became downregulated at the prospective forebrain floor plate, or allowed to identify an early roof plate domain (dorsoventral pattern). Peculiarities of the telencephalon (initial specification and differentiation of pallium versus subpallium) are contemplated. The basic anterior forebrain subdivisions seem to acquire correlated specification and fate mapping patterns around stage HH8.