Leaf epidermal features of Rhododendron (Ericaceae)from China and their systematic significance

Rhododendron is the largest genus within the subfamily Rhododendroideae, which has about 1000 known species in the world and more than 500 species in China. Since the genus was established by Linnaeus, its infrageneric relationships have been well studied by many taxonomists on the basis of morphological characters and molecular data. In 1996, Chamberlain et al. proposed a new system of Rhododendron with eight subgenera, i.e., Azaleastrum, Candidastrum, Hymenanthes, Mumeazalea, Pentanthera, Rhododendron, Therorhodion, and Tsutsusi. In this paper, micromorphological characters of leaf epidermis in 4 varieties, 48 species, 6 subgenera of Rhododendron from China were examined using light microscopy (LM) and scanning electron microscopy (SEM). Leaf epidermal features are described and micromorphological types are distinguished here according to morphological characters such as scale, gland, foliar trichome and stomatal apparatus of leaf epidermis. It is shown that the leaf epidermal cells are usually irregular or polygonal in shape. The patterns of anticlinal walls are straight, arched or undulate. The stomatal apparatuses are anomocytic and are usually found on abaxial, not adaxial, epidermis. The results also show that: (1) the lepidote rhododendron (i.e., subgen. Rhododendron), which has both scales and papillae on leaf epidermis, differs distinctly from the elepidote rhododendron; (2) three types of leaf epidermis are identified in subgen. Hymenanthes (i.e., R. fortunei-type, R. chihsinianum-type and R. simiarum-type), whereas four in subgen. Tsutsusi (i.e., R. mariesii-type, R. simsii-type, R. mariae-type and R. flosculum-type); (3) except for R. westlandii and R. henryi, the species of subgen. Azaleastrum show similar morphological characters, i.e., dense stomatal apparatuses surrounded by ringed or discontinuous striates; (4) R. molle of subgen. Pentanthera differs from the species of other subgenera on morphological characters such as foliar trichomes, dense stomatal apparatuses with asymmetrical outer stomatal rims surrounded by undulate-striates, and no gland; (5) only R. redowskianum is found with distinct T-pieces at the polar region of guard cells in Rhododendron. The results support the conclusion inferred from molecular systematic studies that subgen. Therorhodion is the basal clade of Rhododendron. Finally, the relationships between the closely related species are also discussed on the basis of leaf epidermal features.     

A Ds-insertion mutant of OSH6 (Oryza sativa Homeobox 6) exhibits outgrowth of vestigial leaf-like structures, bracts, in rice

OSH6 (Oryza sativa Homeobox6) is an ortholog of lg3 (Liguleless3) in maize. We generated a novel allele, termed OSH6-Ds, by inserting a defective Ds element into the third exon of OSH6, which resulted in a truncated OSH6 mRNA. The truncated mRNA was expressed ectopically in leaf tissues and encoded the N-terminal region of OSH6, which includes the KNOX1 and partial KNOX2 subdomains. This recessive mutant showed outgrowth of bracts or produced leaves at the basal node of the panicle. These phenotypes distinguished it from the OSH6 transgene whose ectopic expression led to a “blade to sheath transformation” phenotype at the midrib region of leaves, similar to that seen in dominant Lg3 mutants. Expression of a similar truncated OSH6 cDNA from the 35S promoter (35S::ΔOSH6) confirmed that the ectopic expression of this product was responsible for the aberrant bract development. These data suggest that OSH6-Ds interferes with a developmental mechanism involved in bract differentiation, especially at the basal nodes of panicles. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

In vitro thermal stress induces apoptosis and reduces development of porcine parthenotes

The precise physiological causes that result in reduced development of oocytes after heat shock (HS) are not clear. In this study, apoptosis, heat shock protein70 (hsp70), and in vitro development of porcine oocytes were evaluated after HS. Porcine cumulus-oocyte complexes (COCs) were subjected to in vitro maturation for 42 h. The matured oocytes were then heated at 41.5 degrees C for 0 h (control, C0h), 1 h (HS1h), 2 h (HS2h), or 4 h (HS4h). An additional group of oocytes was cultured for 4 h without HS (control, C4h). In Experiment 1, expression of hsp70 was detected by Western-blotting and no difference between controls and HS groups was observed. In Experiment 2, apoptosis of matured oocytes after HS was examined by Annexin V-FITC and TUNEL. No significant TUNEL-positive signals were detected in the heated oocytes compared to the controls, but the intensity of Annexin V-FITC labeling among different groups increased with length of HS and in vitro culture (P<0.05). Oocytes were parthenogenetically activated by an electric pulse plus 6-DMAP (Experiment 3). Mean (+/-S.E.M.) embryonic development in HS2h (cleavage: 42+/-29%; blastocyst: 11+/-10%) and HS4h (cleavage: 36+/-28%; blastocyst: 11+/-8%) were decreased when compared to those in C0h (cleavage: 63+/-12%; blastocyst: 24+/-14%) and C4h (cleavage: 66+/-8%; blastocyst: 21+/-11%). Numbers of blastocysts with TUNEL-positive signals were similar among groups, but the signals increased before the eight-cell stage in HS groups (P<0.05). In conclusion, developmental competence of matured pig oocytes was compromised after heat shock, but it was not closely associated with the expression of oocyte hsp70. However, there may be a link between apoptosis and developmental competence of porcine oocytes.     

Kinetic study of phenol hydroxylase and catechol 1,2-dioxygenase biosynthesis by <Emphasis Type="Italic">Candida tropicalis</Emphasis> cells grown on different phenolic substrates

When Candida tropicalis was grown on phenol, catechol or resorcinol, the highest levels of specific activity of phenol hydroxylase (EC. 1.14.13.7) and catechol 1,2-dioxygenase (EC. 1.13.11.1) were attained with phenol. With the three aromatic compounds tested, the yeast cells exhibited sharp peaks of specific activity of both enzymes at particular incubation times. Phenol-induced cells containing high levels of both enzymes were capable of degrading rapidly and without delay 4-chlorophenol and 2,6-dichlorophenol, and to a lesser extend pentachlorophenol. However, the yeast could not grow on chlorophenols as major carbon and energy source.     

Two enzymes in one; two yeast peroxiredoxins display oxidative stress-dependent switching from a peroxidase to a molecular chaperone function

Although a great deal is known biochemically about peroxiredoxins (Prxs), little is known about their real physiological function. We show here that two cytosolic yeast Prxs, cPrxI and II, which display diversity in structure and apparent molecular weights (MW), can act alternatively as peroxidases and molecular chaperones. The peroxidase function predominates in the lower MW forms, whereas the chaperone function predominates in the higher MW complexes. Oxidative stress and heat shock exposure of yeasts causes the protein structures of cPrxI and II to shift from low MW species to high MW complexes. This triggers a peroxidase-to-chaperone functional switch. These in vivo changes are primarily guided by the active peroxidase site residue, Cys(47), which serves as an efficient "H(2)O(2)-sensor" in the cells. The chaperone function of these proteins enhances yeast resistance to heat shock.     

Genetic selection system for improving recombinant membrane protein expression in E. coli

A major barrier to the physical characterization and structure determination of membrane proteins is low yield in recombinant expression. To address this problem, we have designed a selection strategy to isolate mutant strains of Escherichia coli that improve the expression of a targeted membrane protein. In this method, the coding sequence of the membrane protein of interest is fused to a C‐terminal selectable marker, so that the production of the selectable marker and survival on selective media is linked to expression of the targeted membrane protein. Thus, mutant strains with improved expression properties can be directly selected. We also introduce a rapid method for curing isolated strains of the plasmids used during the selection process, in which the plasmids are removed by in vivo digestion with the homing endonuclease I‐CreI. We tested this selection system on a rhomboid family protein from Mycobacterium tuberculosis (Rv1337) and were able to isolate mutants, which we call EXP strains, with up to 75‐fold increased expression. The EXP strains also improve the expression of other membrane proteins that were not the target of selection, in one case roughly 90‐fold.     

留学生组织学全英文教学的探索与实践

我教研室已承担留学生组织学教学多年,在对留学生进行组织学全英文授课的教学实践中,为了提高教学质量,我们从课程安排、教材选用、教学方法、教学手段以及考试与成绩等方面进行了的探索和改革,并对留学生教学中遇到的语言交流问题进行分析,总结了提高外语水平的经验.本文就留学生组织学教学的探索与实践作了介绍,以便大家互相交流经验,共同提高.     

Further discussion about the features of Lake Puma Yum Co, South Tibet, China

Further discussion about the limnological features of Lake Puma Yum Co, South Tibet, China, is provided based on the results of several investigations. By using depth data from all over the lake, the whole submarine topography has been compiled. Horizontal analysis of the water's physicochemical features indicates that compared with the relatively uniform water features at other lake areas, apparent spatial heterogeneity exists in the water of the subaquatic alluvial fan induced by the Jiaqu River, the biggest inflow. Vertical analysis of water characteristics using two-factor analysis of variance with no re-experiment indicates that temperature, dissolved oxygen, and pH of the water vary with water depth rhythmically, whereas other parameters demonstrate no evident vertical variation, which shows that chemical stratification is not obvious. But this does not exclude slightly higher concentrations of Ca²⁺ induced by lower pH at the bottom of deep lake water. The hydrochemistry difference between inflow water and lake water reveals the loss of Ca²⁺ in lake water, which indicates calcite deposition may be an important characteristic of lake sediment.     

A series of novel directional cloning and expression vectors for blunt-end ligation of PCR products

Novel directional cloning and expression vectors were developed for blunt-end ligation of PCR products that are suitable for high-throughput cloning and simplifying the screening procedure. The PCR products, without further processing, are cloned into vectors digested with SchI and, following transformation, the desired recombinants give typical blue colonies on selectable plates. The principle of this selection strategy is that the construction also generates a full-length ideal lacO gene. To the best of our knowledge, this is the first time that this lacO reconstruction strategy has been applied in the selection of recombinants.     

Rat liver mitochondria impairments under acute carbon tetrachloride-induced intoxication. Effects of melatonin

The aim of the present work was to investigate the mechanisms of oxidative damage of rat liver mitochondria in vitro, under hypochlorous acid (HOCl)-induced oxidative stress, and in vivo, under acute carbon tetrachloride-induced intoxication in rats. Hypochlorous acid (50–300 μM), the main inflammatory agent, inhibited liver mitochondria respiratory activity and caused uncoupling in the respiratory and phos-porylation processes. The toxic damage of rat liver after 24 h of acute carbon tetrachloride-induced intoxication (4 g/kg, intragastrically) was accompanied by a significant reduction in succinate- and glutamate-dependent respiration rate in state 3 (by 65%, p < 0.001, and by 50%, p < 0.01, respectively). The respiration control ratio approached 1, reflecting the loss of respiration control. The phosphorylation coefficient significantly decreased due to uncoupling of the oxidation and phosphorylation processes. The mitochondrial alterations were associated with oxidation of intramitochondrial GSH by 25% (p < 0.05), the marked inhibition of succinate dehydrogenase (complex II) by 35% (p < 0.05), and the rise of blood plasma nitric oxide level by 45% (p < 0.05). The impairment of mitochondrial respiratory function may result from the inhibition of enzymatic activities in the respiratory chain and the damage of mitochondrial membrane during intoxication and plays a key role in the development of the CCl₄-induced hepatotoxicity. Melatonin administration under CCl₄-induced intoxication (three times at a dose of 10 mg/kg) increased the rate of succinate oxidation in state 3 by 30% (p < 0.05) and reversed the increase in glutathione peroxidase activity. Melatonin prevented an elevation of nitric oxide level in the blood plasma of intoxicated animals but did not protect mitochondrial functions under acute intoxication.