A method for inducing xylem emboli in situ: experiments with a field-grown tree

A pressure collar, assembled around 25cm sections of 4-year-old willow twigs, was used to examine cavitation events under field conditions. When the air pressure inside the collar was raised to between 1–8 and 2–8MPa, ultrasound acoustic emission signals were triggered which indicated the breaking of water columns in the xylem. The hydraulic conductivity of the twig portion inside the chamber decreased markedly. As a result, water potentials and conductances in leaves at the end of the twig decreased. Similar changes were induced at comparable pressures in detached twigs. The equipment used is described in detail, and evidence is presented that the mechanism of this artificial production of emboli follows the air-seeding principle hypothesized for natural cavitation events.     

A molecular phylogeny of the genus Apis suggests that the Giant Honey Bee of the Philippines,A. breviligula Maa,and the Plains Honey Bee of southern India,A. indica Fabricius,are valid species

Two new taxa have been added to the existing molecular phylogenies of the genus Apis. The new phylogeny supports the accepted phylogenetic relationships of {dwarf honey bees [giant honey bees (cavity‐nesting honey bees)]}. Based on Bayesian and maximum parsimony trees, our analysis supports recognition of Apis indica, the Plains Honey Bee of south India, as a separate species from A. cerana. Our analysis also supports recognition of the Giant Philippines Honey Bee, A. breviligula, as a separate species from A. dorsata.     

稻纵卷叶螟迁飞途径的研究

稻纵卷叶螟 Cnaphalocrocis medinalis Guenee原为我国水稻上一种间歇性、局部性发生的害虫,随着耕作改制、品种更新、密植高肥等生产水平的提高,为害程度从1965年开始在全国范围内明显上升,已成为水稻上一种常发性的重要害虫。分布东自台湾,西迄西藏,南起海南岛,北到黑龙江,遍及二十八个省、市自治区,主要为害区在泰沂山区到秦岭一线以南各省稻区,及华北、东北渤海湾沿岸地区。国外分布主要在亚洲高温多雨的热带、亚热带及夏季高温多雨的温带地区,以南亚、东南亚各国及日本、朝鲜等地为主,其他     

自发性高血压大鼠中枢血管紧张素Ⅱ的变化对中枢肾上腺素和去甲肾上腺素含量的影响

自发性高血压大鼠中枢肾上腺能递质含量异常,然其原因仍不清楚。本工作发现:12周龄易卒中型自发性高血压大鼠(SHRSP)脑桥,下丘脑后部、尾核中去甲肾上腺素(NE)含量及延髓、下丘脑前部,下丘脑后部中肾上腺素(E)含量均高于同龄 Wista Kyoto 大鼠(WKY),SHRSP 中枢 AⅡ含量亦明显高于同龄 WKY;向8周龄 SHRSP 和 WKY 侧脑室慢性灌注巯甲丙脯氨酸,不仅降低动脉血压及各脑区AⅡ含量,亦使中枢 NE 及 E 水平下降,但巯甲丙脯氨酸对 SHRSP 的影响远较对 WKY 明显。结果提示:SHRSP 中枢肾上腺能递质含量增加可能与 SHRSP 中枢 AⅡ量含量升高以及 SHRSP 中枢 AⅡ对中枢肾上腺能递质的促释放调节机制明显易化有关。     

Leaf anatomical properties in relation to differences in mesophyll conductance to CO2 and photosynthesis in two related Mediterranean Abies species

Abies alba and Abies pinsapo are closely related species with the same ribulose 1·5‐bisphosphate carboxylase/oxygenase (Rubisco) large subunit (rbcL) but contrasting hydraulic traits and mesophyll structure occurring in the Iberian Peninsula under contrasting conditions. As photosynthesis and hydraulic capacities often co‐scale, we hypothesize that these species differ in mesophyll conductance to CO₂ (g_m). g_m and key anatomical traits were measured in both species. Drought‐adapted population of A. pinsapo has higher photosynthesis than the more mesic population of A. alba, in agreement with its higher hydraulic capacity. However, A. alba exhibits the largest stomatal conductance (g_s), and so water use efficiency (WUE) is much higher in A. pinsapo. The differences in photosynthesis were explained by differences in g_m, indicating a correlation between hydraulic capacity and g_m. We report a case where g_m is the main factor limiting photosynthesis in one species (A. alba) when compared with the other one (A. pinsapo). The results also highlight the discrepancy between g_m estimates based on anatomical measurements and those based on gas exchange methods, probably due to the very large resistance exerted by cell walls and the stroma in both species. Thus, the cell wall and chloroplast properties in relation to CO₂ diffusion constitute a near‐future research priority.     

Charge attraction and beta propensity are necessary for amyloid fibril formation from tetrapeptides

Amyloid fibrils in which specific proteins have polymerized into a cross-beta-sheet structure are found in about 20 diseases. In contrast to the close structural similarity of fibrils formed in different amyloid diseases, the structures of the corresponding native proteins differ widely. We show here that peptides as short as 4 residues with the sequences KFFE or KVVE can form amyloid fibrils that are practically identical to fibrils formed in association with disease, as judged by electron microscopy and Congo red staining. In contrast, KLLE or KAAE do not form fibrils. The fibril-forming KFFE and KVVE show partial beta-strand conformation in solution, whereas the non-fibril-forming KLLE and KAAE show random structure only, suggesting that inherent propensity for beta-strand conformation promotes fibril formation. The peptides KFFK or EFFE do not form fibrils on their own but do so in an equimolar mixture. Thus, intermolecular electrostatic interactions, either between charged dipolar peptides or between complementary charges of co-fibrillating peptides favor fibril formation.     

Controlling polymerization of beta-amyloid and prion-derived peptides with synthetic small molecule ligands

The Alzheimer beta-amyloid peptide (Abeta) and a fragment of the prion protein have the capacity of forming amyloid-like fibrils when incubated under physiological conditions in vitro. Here we show that a small amyloid ligand, RO-47-1816/001, enhances this process severalfold by binding to amyloid molecules and apparently promote formation of the peptide-to-peptide bonds that join the monomers of the amyloid fibrils. This effect could be antagonized by other ligands, including analogues of RO-47-1816/001, as well as the structurally unrelated ligand Congo red. Analogues of RO-47-1816/001 with low affinity for amyloid did not display any antagonistic effect. In conclusion, these data suggest that synthetic molecules, and possibly also small natural substances present in the brain, may act in a chaperone-like fashion, promoting Abeta polymerization and growth of amyloid fibrils in vitro and possibly also in vivo. Furthermore, we demonstrate that small organic molecules can be used to inhibit the action of amyloid-enhancing compounds.