Comparative ultrastructure and gas exchange characteristics of the C3–C4 intermediate Neurachne minor S. T. Blake (Poaceae)

Abstract Ultrastructural and physiological characteristics of the C₃-C₄ intermediate Neurachne minor S. T. Blake (Poaceae) are compared with those of C₃ and C₄ relatives, and C₃-C₄Panicum milioides Nees ex Trin. N. minor consistently exhibits very low CO₂ compensation points (τ: 1.0, usually 0.3–0.6 Pa) yet has C₃-like δ¹³C values. CO₂ assimilation rates (A) respond like those of C₃ plants to a decrease in O₂ partial pressure (2 × 104–1.9 × 103 Pa) at ambient CO₂ levels, but this response is progressively attenuated until negligible at very low CO₂. By contrast, other species of the Neurachneae are clearly either C₄ (two spp.) or C₃ (seven spp.). For plants grown and measured at different photon flux densities (PFDs), τ for N. minor and P. milioides increases from 0.5 to 1.0, and from 1.0 to 2.1 Pa, respectively, as PFD is decreased from 1860 to 460 μmol m^?2s^?1. In N. minor, the O₂ response of τ is either biphasic as in P. milioides, but much diminished and with a higher transition point, or is very C₄-like. As in C₄ relatives, inner sheath cells contain numerous chloroplasts. Their walls possess a suberized lamella, which may make them more CO₂-tight than bundle sheath cells of P. milioides, contributing to the almost C₄-like τ characteristics of N. minor. The biochemical basis of C₃-C₄ intermediacy is considered.     

Structural relationship between tRNA2 Lys and tRNA4 Lys from mouse lymphoma cells

Summary Mouse lymphoma cells have three major isoaccepting lysine tRNAs. Two of these isoacceptors, tRNA₂ ^Lys and tRNA₄ ^Lys, were sequenced by rapid gel or chromatogram readout methods. They have the same primary sequence but differ in two modified nucleotides. tRNA₄ ^Lys has an unmodified uridine replacing one dihydrouridine and an unidentified nucleotide, t⁶A^*, replacing t⁶A. This unidentified nucleotide is not a hypomodified form of t⁶A. Thus, tRNA4ys is not a simple precursor of tRNA₂ ^Lys. Both tRNAs have an unidentified nucleotide, U^**, in the third position of the anticodon. Also, partial sequences of minor homologs of tRNA₂ ^Lys and tRNA₄ ^Lys were obtained. The distinctions between tRNA₂ ^Lys and tRNA₄ ^Lys may be part of significant cellular roles as illustrated by the differential effects of these isoacceptors on the synthesis by lysyl-tRNA synthetase of diadenosine-5,5-P₁,P₄-tetraphosphate, a putative signal in DNA replication.     

Developmental response of zygotes exposed to similar mutagens

Exposure of mouse zygotes to ethylene oxide (EtO) or ethyl methanesulfonate (EMS) led to high incidences of fetal death and of certain classes of fetal malformations (Generoso et al., 1987, 1988; Rutledge and Generoso, 1989). These effects were not associated with induced chromosomal aberrations (Katoh et al., 1989) nor are they likely to be caused by gene mutations (Generoso et al., 1990). Nevertheless, the anomalies observed in these studies resemble the large class of stillbirths and sporadic defects in humans that are of unknown etiology, such as cleft palate, omphalocoel, clubfoot, hydrops and stillbirths (Czeizel, 1985; Oakley, 1986). Therefore, we continue to study the possible mechanisms relating to induction of these types of zygote-derived anomalies in mice. Effects of zygote exposure to the compounds methyl methanesulfonate (MMS), dimethyl sulfate (DMS), and diethyl sulfate (DES), which have similar DNA-binding properties as EtO and EMS, were studied. DMS and DES, but not MMS, induced effects that are similar to those induced by EtO and EMS. Thus, no site-specific alkylation product was identifiable as the critical target for these zygote-derived anomalies. We speculate that the developmental anomalies arose as a result of altered programming of gene expression during embryogenesis.     

The formation of “compartment replicas” in the lymph nodes of athymic animals

Summary This communication describes a new anomaly that can affect the capsule of lymph nodes of athymic animals. Lymphocytes infiltrate a segment of the capsule above the variably atrophied peripheral cortex overlying the center of the deep-cortex unit of a node compartment. Lymphocytes thereafter form a capsular mass. The developing mass of lymphocytes is invaded by outgrowths of the node's subcapsular sinus while it fuses with the parenchyma of the related node compartment. Eventually, this new nodal element acquires structures resembling those of nodes and becomes a more or less exact replica of the original node compartment. Replicas stem from node compartments that are overchallenged by uncontrolled antigens. Aspects of the formation of replicas are explained by recent findings on events occurring in nodes of athymic animals and on the pattern of antigen distribution in the subcapsular sinus of a node. It is concluded that the formation of a compartment replica constitutes a mechanism allowing the organism to compensate somewhat for the partial atrophy or deficiency of a node compartment.Work funded by the Medical Research Council of Canada     

Primary structure of two nonallelicβ-globin chains from DBA/2 mice

The amino acid sequences of the major and minor globin chains from DBA/2 mice have been determined. This information is of interest because DBA/2 mice are the strain of origin for most murine erythroleukemia lines. The primary structure of DBA/2 globins agrees completely with that predicted from the coding properties of BALB/c globin genes. This identity does not support a rapid evolutionary divergence in inbred mouse strains, at least at these loci in these strains.This work was supported in part by National Institutes of Health Grants AM26956, HL24908, and AM14923 and by the Department of Energy under Contract DE-AC05-840R21400 with Martin Marietta Systems. The SUNY Buffalo Sequencing Facility was supported by a grant from the James Cummings Foundation and National Institutes of Health Grants RR05400 and RR07066.     

Orientation anomalies (reversal) of the four-spotted megrim (Lepidorhombus boscii) in the Aegean Sea

Reversal occurred in four out of 15 325 specimens (0·026%) of four-spotted megrim Lepido-rhombus bascii caught in the Aegean Sea.     

Taurodont, pyramidal and fused molar roots associated with other anomalies in a kindred

Crown characteristics have been the parameter most frequently utilized in studies of tooth morphology. Dental root structures have received relatively little attention. Examination of unusual molar roots in a kindred has enabled us to (1) establish a typology for classifying molar roots, (2) devise a methodology for evaluating the degree of taurodontism and (3) hypothesize about phylogenetic, ontogenetic and genetic aspects of root morphology. The roots of molar teeth were studied radiographically in 20 members of a family of English–German ancestry in which there was no consanguinity. Taurodont, pyramidal (single conical root) and fused molar roots were common. Other ectodermal and mesodermal anomalies (unusual upper lip, glaucoma, syndactyly and clinodactyly) were also present. This unique constellation of dental, cutaneous, ocular and bone abnormalities constitutes a previously undescribed syndrome. Unusual roots may be a genetic marker, and the finding of unusual roots, such as prismatic or wholly pyramidal, should prompt a search for other abnormalites. Dental trait analysis for genetic and microevolutionary studies should include root, as well as crown, characteristics.     

我院三十年消化系统恶性肿瘤病理统计分析

目的:了解烟台地区消化系统恶性肿瘤在过去不同年代的流行病学和发病学特点,以期为本地区恶性肿瘤的防治研究工作提供参考价值。方法:通过对烟台毓璜顶医院1971年-2000年经病理确诊的消化系统恶性肿瘤进行统计分析,统计了每十年为一个时间段内的主要发病部位的所有原发性恶性肿瘤,分析不同时间段的各器官恶性肿瘤的构成百分比、发病年龄、男女比例等流行病学特点,并将结果与国内外的统计资料进行比较和分析。结果:三个年代消化系统恶性肿瘤的检出率呈增加趋势,共检出恶性肿瘤8295例。胃癌及大肠癌是消化系统发病率最高的两种恶性肿瘤。结论:消化系统肿瘤高发提示胶东地区居民的食物种类、饮食习惯中存在不利于健康的因素。