An anatomical study of anther development in Acorus L.: Phylogenetic implications

 Critical morphological synapomorphies have not been found in support of the Acoranan hypothesis, the molecular phylogenetic discovery that Acoranae are the basal monocots. The previously undetermined pattern of anther wall development in Acorus has been suggested to be one such character. Two main types of anther wall development have been recognized: 1) the “monocotyledonous” type, which characterizes both monocots and dicots, and 2) the “dicotyledonous” type, which is almost exclusively found among dicots. An anatomical study of anther wall development in Acorus was here undertaken using the electron microscope. Development of the anther wall in Acorus was found to be somewhat irregular or perhaps even intermediate between the two types although largely consistent with the “monocotyledonous” type. The presumed significance of anther wall development and other critical morphological characters to the Acoranan hypothesis in the absence of knowledge about the sister group to the monocots is evaluated. Received August 28, 2000 Accepted February 19, 2001     

Site in the cat-86 regulatory leader that permits amicetin to induce expression of the gene.

Expression of the plasmid gene cat-86 is induced in Bacillus subtilis by two antibiotics, chloramphenicol and the nucleoside antibiotic amicetin. We proposed that induction by either drug causes the destabilization of a stem-loop structure in cat-86 mRNA that sequesters the ribosome-binding site for the cat coding sequence. The destabilization event frees the ribosome-binding site, permitting the initiation of translation of cat-86 mRNA. cat-86 induction is due to the stalling of a ribosome in a leader region of cat-86 mRNA, which is located 5' to the RNA stem-loop structure. A stalled ribosome that is active in cat-86 induction has its aminoacyl site occupied by leader codon 6. To test the hypothesis that a leader site 5' to codon 6 permits a ribosome to stall in the presence of an inducing antibiotic, we inserted an extra codon between leader codons 5 and 6. This insertion blocked induction, which was then restored by the deletion of leader codon 6. Thus, induction seems to require the maintenance of a precise spatial relationship between an upstream leader site(s) and leader codon 6. Mutations in the ribosome-binding site for the cat-86 leader, RBS-2, which decreased its strength of binding to 16S rRNA, prevented induction. In contrast, mutations that significantly altered the sequence of RBS-2 but increased its strength of binding to 16S rRNA did not block induction by either chloramphenicol or amicetin. We therefore suspected that the proposed leader site that permitted drug-mediated stalling was located between RBS-2 and leader codon 6. This region of the cat-86 leader contains an eight-nucleotide sequence (conserved region I) that is largely conserved among all known cat leaders. The codon immediately 5' to conserved region I differs, however, between amicetin-inducible and amicetin-noninducible cat genes. In amicetin-inducible cat genes such as cat-86, the codon 5' to conserved region I is a valine codon, GTG. The same codon in amicetin-noninducible cat genes is a lysine codon, either AAA or AAG. When the GTG codon immediately 5' to conserved region I in cat-86 was changed to AAA, amicetin was no longer active in cat-86 induction, but chloramphenicol induction was unaffected by the mutation. The potential role of the GTG codon in amicetin induction is discussed.     

Analysis of the regulatory sequences needed for induction of the chloramphenicol acetyltransferase gene cat-86 by chloramphenicol and amicetin.

Induction of the chloramphenicol acetyltransferase gene cat-86 in Bacillus subtilis results from the activation of translation of cat-86 mRNA. The inducers, chloramphenicol and amicetin, are thought to enable ribosomes to destabilize a stem-loop structure in cat-86 mRNA that sequesters the ribosome binding site for the cat-86 coding sequence, designated RBS-3. The region of cat-86 mRNA which is 5' to the stem-loop contained two additional ribosome binding sites, RBS-1 and RBS-2, located 84 and 56 nucleotides, respectively, upstream from RBS-3. RBS-1 and RBS-2 were each followed by a potential translation initiation codon and a short open reading frame. Bal 31-generated deletions into the 5' end of the regulatory region that removed RBS-1 but did not enter RBS-2 caused a fourfold decrease in the uninduced and chloramphenicol-induced level of cat-86 expression and a more than 10-fold reduction in the amicetin-induced level of expression. Deletions that removed both RBS-1 and RBS-2 but did not enter the stem-loop abolished both chloramphenicol- and amicetin-inducible expression. These data indicate that RBS-2 and sequences 3' to RBS-2 are minimally essential to chloramphenicol induction. However, the presence of RBS-1 in the mRNA elevated the maximum level of expression obtained during chloramphenicol induction. These studies also demonstrate that induction of cat-86 by amicetin is highly dependent on RBS-1. To determine whether a correlation existed between RBS-1 and amicetin inducibility, we examined the sequence of the regulatory regions for two natural variants of cat-86, cat-66 and cat-57, which are chloramphenicol inducible but are very poorly induced by amicetin. Both contained nucleotide sequence differences from cat-86 in the vicinity of RBS-1 that would prevent translation of the leader peptide associated with RBS-1 in cat-86. In contrast, the regulatory regions got the three genes were virtually identical in the vicinity of RBS-2. These data indicate that efficient induction by amicetin requires sequences that are not essential for induction by chloramphenicol.     

Studies of activating and nonactivating metal ion binding to yeast enolase

Measurements of binding of certain divalent cations to yeast apoenolase were made using a pH-meter, chromatography, a divalent cation electrode, and ultrafiltration. The binding of the activating metal ions Mg2+ and Co2+ and the nonactivator Ca2+ were studied as functions of the presence or absence of substrate/product, phosphate, and fluoride or level of Tb3+. The data suggest phosphate and fluoride increase Mg2+ binding but not Ca2+ binding. Substrate/product appears to increase Ca2+ binding as well as that of Mg2+ and Co2+. In the presence of substrate, Co2+ binding was 5-6 mol/mol dimer. In the absence of substrate/product, Tb3+ reduced Co2+ binding from 4 mol/mol to 2. These data are interpreted in terms of binding to "conformational," "catalytic" (substrate/product dependent), and "inhibitory" sites. Measurements of Tb3+ fluorescence quenching by Co2+ suggested that the distance between "conformational" sites on the two subunits was large, while the distance between "conformational" and "inhibitory" sites was ca. 17 +/- 4 A. Potentiometric titrations of apoenzyme with Ca2+ and Mg2+ showed that the metal ions produced the same proton release in the presence or absence of substrate/product. If phosphate and fluoride were present, then more protons were released if Ca2+ was the titrant rather than Mg2+, suggesting a difference in ionization state in the complex with the activating metal. Electron paramagnetic resonance studies of Co2+ binding to the various sites in the enzyme are presented. The Co2+ bound to all three sites appears to be high spin, consistent with a preponderance of oxyligands in an octahedral environment. Substrate, citrate, and a strongly binding substrate analogue strongly enhance the hyperfine structure of conformational Co2+. This is interpreted as the result of a change in interaction of an axial ligand to conformational Co2+ produced by carbon-3 of substrate or analogue.     

蚕豆叶片发育与衰老过程中超氧物歧化酶活性与丙二醛含量变化

蚕豆植株叶片随茎节自上而下表现出明显的发育与衰老顺序,可作为衰老特征的是叶绿素和蛋白质含量明显下降。蚕豆叶中SOD活性主要定位于12 000× g离心后所得的上清液和叶绿体组分。衰老叶片的SOD总活性和叶绿体组分的相对活性都有所下降,SOD同工酶谱也发生了改变。O_2~ 产生速率随叶龄增大而稍上升;而MDA含量在叶片外观表现枯黄衰老征兆前就急剧上升。可能因为衰老叶片过氧化氢酶活性大幅度下降与SOD之间的不平衡,致使O_2~ 代谢中间产物累积而引起膜的损伤.     

Alliances of Muhlenbergia (Poaceae) within New World Eragrostideae are identified by phylogenetic analysis of mapped restriction sites from plastid DNAs

Restriction sites for six enzymes were mapped for the plastid DNAs of 25 species of Eragrostideae, one species of Cynodonteae (Eustachys distichophylla), and one species of Pooideae. Of the 124 restriction sites observed, 67 were variably present and shared by two or more species. These data were analyzed by the parsimony method using equal and unequal weights and by bootstrap analysis. The cladistic analyses established that members of the Muhlenbergiinae, including the genera Muhlenbergia, Blepharoneuron, Bealia, Chaboissaea, Lycurus, and Pereilema, share seven restriction site mutations and are strongly supported by the data as a monophyletic subtribe. Surprisingly, Redfieldia flexuosa also clustered with the Muhlenbergiinae in the analysis, perhaps indicative of a past interspecific hybridization event. The restriction sites data also weakly support a relationship (six shared mutations) between Erioneuron, Munroa, and Dasyochloa.