Systematics of Mukdenia and Oresitrophe (Saxifragaceae): Insights from genome skimming data

Oresitrophe and Mukdenia (Saxifragaceae) are epilithic sister genera used in traditional Chinese medicine. The taxonomy of Mukdenia, especially of M. acanthifolia, has been controversial. To address this, we produced plastid and mitochondrial data using genome skimming for Mukdenia acanthifolia and Mukdenia rossii, including three individuals of each species. We assembled complete plastomes, mitochondrial CDS and nuclear ribosomal ETS/ITS sequences using these data. Comparative analysis shows that the plastomes of Mukdenia and Oresitrophe are relatively conservative in terms of genome size, structure, gene content, RNA editing sites and codon usage. Five plastid regions that represent hotspots of change (trnH-psbA, psbC-trnS, trnM-atpE, petA-psbJ and ccsA-ndhD) are identified within Mukdenia, and six regions (trnH-psbA, petN-psbM, trnM-atpE, rps16-trnQ, ycf1 and ndhF) contain a higher number of species-specific parsimony-informative sites that may serve as potential DNA barcodes for species identification. To infer phylogenetic relationships between Mukdenia and Oresitrophe, we combined our data with published data based on three different datasets. The monophyly of each species (Oresitrophe rupifraga, M. acanthifolia and M. rossii) and the inferred topology ((M. rossii, M. acanthifolia), O. rupifraga) are well supported in trees reconstructed using the complete plastome sequences, but M. acanthifolia and M. rossii did not form a separate clade in the trees based on ETS + ITS data, while the mitochondrial CDS trees are not well-resolved. We found low recovery of genes in the Angiosperms353 target enrichment panel from our unenriched genome skimming data. Hybridization or incomplete lineage sorting may be the cause of discordance between trees reconstructed from organellar and nuclear data. Considering its morphological distinctiveness and our molecular phylogenetic results, we strongly recommend that M. acanthifolia be treated as a distinct species.     

The genus Cabomba (Cabombaceae)–a taxonomic study

The genus Cabomba (Cabombaceae) is revised. Five species and three varieties are recognized: C. aquatica, C. palaeformis, C. furcata, C. haynesii and C. caroliniana including var. caroliniana , var. pulcherrima , and var. flavida var. nov. A basic chromosome number of x = 13 is proposed. Special emphasis has been given to pollen and seed morphology as revealed by SEM studies.     

EFFECT OF LEAF ANGLE AND ORIENTATION ON PHOTOSYNTHESIS AND WATER RELATIONS IN SILPHIUM TEREBINTHINACEUM

Leaf angle and orientation were measured for 217 leaves from two populations of Silphium terebinthinaceum Jacq., a prairie forb with large, unlobed leaves. Seventy-five percent of leaves measured had an angle of deviation from horizontal of more than 60°, and 60% were oriented within 15° of North. Incident Photon Flux Density (PFD), leaf temperature, photosynthesis, stomatal conductance to CO₂, internal CO₂ concentration, transpiration, and water use efficiency (WUE) were measured on 67 pairs of leaves with the axes oriented in either a North-South (N–S) or East–West (E–W) direction. Leaves with axes oriented N–S intercepted higher levels of PFD during morning and afternoon and exhibited higher diurnal rates of photosynthesis and WUE. Leaf temperature was reduced in N–S leaves during midday as compared to E–W leaves, and was lower in vertical leaves than in those in a horizontal position. Therefore, it was concluded that leaf orientation and verticality enhance carbon gain and minimize water loss—characteristics which may have adaptive significance in a hot, stressful prairie environment.     

First chemical synthesis of a scorpion alpha-toxin affecting sodium channels: the Aah I toxin of Androctonus australis hector.

Aah I is a 63-residue alpha-toxin isolated from the venom of the Buthidae scorpion Androctonus australis hector, which is considered to be the most dangerous species. We report here the first chemical synthesis of Aah I by the solid-phase method, using a Fmoc strategy. The synthetic toxin I (sAah I) was renatured in DMSO-Tris buffer, purified and subjected to thorough analysis and comparison with the natural toxin. The sAah I showed physico-chemical (CD spectrum, molecular mass, HPLC elution), biochemical (amino-acid composition, sequence), immunochemical and pharmacological properties similar to those of the natural toxin. The synthetic toxin was recognized by a conformation-dependent monoclonal anti-Aah I antibody, with an IC50 value close to that for the natural toxin. Following intracerebroventricular injection, the synthetic and the natural toxins were similarly lethal to mice. In voltage-clamp experiments, Na(v) 1.2 sodium channel inactivation was inhibited by the application of sAah I or of the natural toxin in a similar way. This work describes a simple protocol for the chemical synthesis of a scorpion alpha-toxin, making it possible to produce structural analogues in time.     

Does photorespiration protect the photosynthetic apparatus in french bean leaves from photoinhibition during drought stress?

Dithiothreitol (DTT), an inhibitor of violaxanthin de-epoxidation and zeaxanthin formation in chloroplasts, inhibited blue-light-stimulated stomatal opening in epidermal peels of Vicia faba L. in a concentration-dependent fashion. Complete inhibition was observed at 3 mM DTT. The DTT effect was specific for the stomatal response to blue light, and the red-light-stimulated opening, which depends on photosynthetic reactions in the guard cells, was unaffected. Preirradiation of stomata in epidermal peels with increasing photon fluence rates of red light, prior to an incubation in 10 mol·m^-2·s^-1 of blue light and 100 mol·m^-2·s^-1 red light, resulted in a DTT-sensitive, blue-light-stimulated opening that was proportional to the fluence rate of the red light pre-treatment. Guard cells in epidermal peels and guard-cell protoplasts irradiated with red light showed increases in their zeaxanthin content that depended on the fluence rate of red light, or on the incubation time. The increases in zeaxanthin concentration were inhibited by DTT. The obtained results indicate that zeaxanthin could function as a photoreceptor mediating the stomatal responses to blue light.Abbreviation DTT dithiothreitol This work was supported by grants from the National Science Foundation and the US Department of Energy to E.Z.     

Seasonal variation in positional behavior of malagasy lemurs

I describe the positional behavior of four species of Malagasy lemur (Propithecus diadema, Eulemur fulvus rufus, Eulemur rubriventer,and Varecia variegata)at two times of year at Ranomafana National Park,Madagascar. There were significant seasonal differences in locomotor behavior in all species except P. diademaAmong the lemurids, leaping was more frequent and quadrupedism less frequent in the dry season. Only E. rubriventerexhibited seasonal differences in posture, and there were few seasonal differences in support use. The observed differences in positional behavior were not the result of differences in activity budget or in microhabitat use attributable to seasonal variation in resource use.     

Regulation of Phenylethanolamine N-Methyltransferase Gene Expression by Imidazoline Receptors in Adrenal Chromaffin Cells

Abstract: As adrenal medullary chromaffin cells express imidazoline binding sites in the absence of α₂-adrenergic receptors, these cells provide an ideal system in which to determine whether imidazolines can influence catecholamine gene expression through nonadrenergic receptors. This study evaluates the ability of clonidine and related drugs to regulate expression of the gene for the epinephrine-synthesizing enzyme phenylethanolamine N -methyltransferase (PNMT) in the rat adrenal gland and in bovine adrenal chromaffin cell cultures. In vivo, PNMT and tyrosine hydroxylase (TH) mRNA levels increase in rat adrenal medulla after a single injection of clonidine. Clonidine also dose-dependently stimulates PNMT mRNA expression in vitro in primary cultures of bovine chromaffin cells, with a threshold dose of 0.1 μ M . Other putative imidazoline receptor agonists, including cimetidine, rilmenidine, and imidazole-4-acetic acid, likewise enhance PNMT mRNA production showing relative potencies that correlate with their binding affinities at chromaffin cell I₁-imidazoline binding sites. The effects of clonidine on PNMT mRNA appear to be distinct from and additive with those exerted by nicotine. Moreover, neither nicotinic antagonists nor calcium channel blockers, which attenuate nicotine's influence on PNMT mRNA production, diminish clonidine's effects on PNMT mRNA. Although 100 μ M clonidine diminishes nicotine-stimulated release of epinephrine and norepinephrine in chromaffin cells, this effect appears unrelated to stimulation of imidazoline receptor subtypes. This is the first report to link imidazoline receptors to neurotransmitter gene expression.     

Clinical phenotype of nephrogenic diabetes insipidus in females heterozygous for a vasopressin type 2 receptor mutation

Nephrogenic diabetes insipidus (NDI) usually shows an X-linked recessive mode of inheritance caused by mutations in the vasopressin type 2 receptor gene (AVPR2). In the present study, three NDI families are described in which females show clinical features resembling the phenotype in males. Maximal urine osmolality in three female patients did not exceed 200 mosmol/kg and the absence of extra-renal responses to 1-desamino-8-d-arginine vasopressin was demonstrated in two of them. All affected females and two asymptomatic female family members were shown to be heterozygous for an AVPR2 mutation. Skewed X-inactivation is the most likely explanation for the clinical manifestation of NDI in female carriers of an AVPR2 mutation. It is concluded that, in female NDI patients, the possibility of heterozygosity for an AVPR2 gene mutation has to be considered in addition to homozygosity for mutations in the aquaporin 2 gene.