New observations on the splenius capitis and rectus capitis ventralis muscles of the Common Swift Apus apus (Apodidae)

In swifts and hummingbirds (Apodiformes), the splenius capitis muscle displays a characteristic modification, the 'cruciform origin'. The muscle pairs arise from the second vertebra by several slips which criss-cross and interdigitate with each other, before inserting into the skull. In the course of a study on the neck muscles of the Common Swift, we paid special attention to the arrangement of these slips of the splenius capitis muscle, and noted a previously unrecognized individual modification of this muscle. In addition, we observed an incipient cruciform origin of the deep portion (slip) of the rectus capitis ventralis muscle that has not been noticed for swifts or any other avian taxon before. The development and function of these modifications of the splenius capitis and rectus capitis ventralis muscle are discussed.     

STUDIES ON THE PRODUCTION AND PHYSIOLOGICAL EFFECTS OF ASYMMETRIN

In shake-flask culture asymmetrin was produced by PenicIlliumthomiiaud Byssochlamys niveaduring autolysis. A bioassay wasdevised to estimate relative concentrations of this compound.Culture filtrates of P. thomiicontaining asymmetrin caused adecrease in wet weight, dry weight, and total nitrogen of Phaseolusvulgarisup to 18 days after treatment. At certain intervalsafter treatment with culture filtrate of B. nivea,respirationwas inhibited, and changes were observed in isotope ratio valuesof plants supplied with glucose-¹⁴ C. Plants treated previouslywith culture filtrates of B. nivearesponded but little to gibberelhcacid. High concentrations of mdoleacetic acid inhibited growthof control plants but stimulated growth of plants treated withculture filtrate of B. nivea. ¹Present address: United Fruit Company, Norwood, Massachusetts.Supported in part by a Public Health Service Fellowship No.GF 13,776 from the division of General Medical Sciences, PublicHealth Service, National Institutes of Health, and Grant G 20989from the National Science Foundation. ²Journal Paper No. 2170 of the Purdue Agricultural ExperimentStation.     

Australia's marine biogeography revisited: Back to the future?

The recognition of broad biogeographic provinces provides an important framework for ecological and conservation biological research. Marine biologists have long recognized distinct biogeographic provinces in southern Australia, primarily on the basis of qualitative differences in intertidal species assemblages. Here we provide an a priori test for these traditional eastern (Peronian), western (Flindersian) and south‐eastern (Maugean) provinces. Specifically, we analyse distributional data for approximately 1500 algal species using the newly available Australian Virtual Herbarium, an online database of herbarium specimens. Our quantitative algal analyses across southern Australia identify three distinct biogeographic assemblages, consistent with traditional qualitative provinces. We argue that these broad provinces provide a highly effective framework for understanding and managing Australia's marine biodiversity. In particular, biogeographic provinces provide a regional framework for integrating the ongoing discovery of biological variation at finer scales. More broadly therefore we recommend that biologists undertake quantitative analyses to test provincial biogeographic boundaries around the globe.     

Cell Adhesion as a Basis of Pattern in Embryonic Development

The development of the modern methodologies of cell biologyin the fifties and sixties and of molecular biology in the seventiesand eighties has led to a reductionist view of embryonic developmentthat centers on the cell and the gene as the functional unitsof development. The functional units in most inductive and morphogeneticprocesses in the embryo are not single cells, however, but ratherare collectives of interacting cells that give rise to the tissuesand organs. Can these methodological developments reconcilea molecular analysis with the fact that form arises epigeneticallyfrom the increasing number of embryonic cells during development?To answer this question one must link genetic regulation tomechanochemical processes that coordinate cell division, cellmovement and cell death. Recent studies of cell adhesion suggestthat one such link is provided by cell adhesion molecules (CAMs)that mediate cell-cell binding. These studies suggest that CAMsare involved in defining cell collectives and their bordersas they interact during inductive events in morphogenesis. AlthoughCAMs cannot be considered the "cause" of induction, they playkey roles among the complex causal chains of inductive interactionsinvolving hormones and growth-factors, extracellular matrixcomponents and cellular receptors. We provide here a brief summaryof modern developments in the field centered about the functionof CAMs in morphogenesis and using recent experimental resultsin the developing feather as a paradigmatic example.     

Identification of Xanthomonas citri ssp. citri host specificity genes in a heterologous expression host

We provide the first conclusive evidence that Xanthomonas axonopodis pv. citri Asiatic strain (Xac-A) and, in particular, Xac-A^w, a unique citrus canker A strain isolated from Key lime in Wellington, Florida, induces a hypersensitive reaction (HR) in grapefruit leaves. Using the heterologous tomato pathogen X. perforans , as a recipient of the Xac-A^w genomic library, we identified a 1599-bp open reading frame responsible for HR in grapefruit, but not Key lime, and designated it avrGf 1. Xac-A^wΔ avrGf 1 produced typical, although visibly reduced, citrus canker symptoms (i.e. raised pustules) in grapefruit and typical canker symptoms in Key lime. We also determined that the X. perforans transconjugant carrying an Xac-A^w hrpG elicited HR in grapefruit and Key lime leaves, and that xopA in X. perforans was partly responsible for HR. Xac-A transconjugants carrying the X. perforans xopA were reduced in ability to grow in grapefruit leaves relative to wild-type Xac-A. The X. perforans xopA appears to be a host-limiting factor. An avrBs3 homologue, which contained 18.5 repeats and induced HR in tomato, was designated avrTaw . This gene, when expressed in a pustule-minus Xac-A^w, did not complement pustule formation; however, pthA^w , a functional pthA homologue, complemented the mutant strain to produce typical pustules in Key lime, but markedly reduced pustules in grapefruit. Both avrBs3 homologues, when expressed in a typical Xac-A strain, resulted in typical citrus canker pustules in grapefruit, indicating that neither homologue suppressed pustule size in grapefruit. Xac-A^w contains other unidentified factors that suppress development in grapefruit.     

Citrate Synthase of Plants: Sensitivity to Sulfhydryl Reagents and Molecular Weight of the Enzyme

Citrate synthase of wheat (Triticum aestivum L.), bean (Phaseolus vulgaris L.), cauliflower (Brassica oleracea L.), and a marine blue-green alga (Coccochloris elabens) is inhibited by sulfhydryl binding reagents. The inhibitions are partially reversed by dithiothreitol. Pig heart citrate synthase is only slightly inhibited by the same reagents and this is completely reversed by dithiothreitol. All citrate synthases in this study are inhibited by adenosine triphosphate. The inhibition is relieved by increasing the concentration of acetyl coenzyme A. Citrate synthase of wheat, cauliflower, bean, and pig heart was estimated by gel filtration to have a molecular weight of 100,000 daltons. The Coccochloris citrate synthase was estimated to have a molecular weight greater than 250,000 daltons. The evolutionary implications of these findings are discussed. This enzyme is comparable in size to the 100,000 dalton mammalian enzyme (Singh et al. 1970) making it somewhat larger than the 65,000 dalton mango enzyme (Srere et al. 1971). The PHMB-treated enzyme also shows changes in its electrophoretic properties (Greenblatt and Sarkissian unpublished). The evidence presented here demonstrates that citrate synthase of various plants is sensitive to sulfhydryl reagents suggesting that sulfhydryl reactivity is a not unusual property of plant citrate synthase. In addition we show that molecular weight as large as or larger than that reported in microbial systems can occur in a blue-green alga.     

ISOLATION AND IDENTIFICATION OF ASYMMETRIN

Asymmetrin was isolated as the sodium salt from culture filtrateof Penicillium thomii. By comparison with hadacidin (N-formylhydroxyamino-acetic acid) we concluded that the two compoundsare identical. ¹Journal Paper No. 2329 of the Purdue Agricultural ExperimentStation. Supported in part by Grant G-20989 from the NationalScience Foundation to R. W. CURTIS. ²Present address: United Fruit Company, Norwood, Massachusetts.     

Comparative Biology of Zebra Mussels in Europe and North America: An Overview

SYNOPSIS. Since the discovery of the zebra mussel, Dreissenapolymorpha, in the Great Lakes in 1988 comparisons have beenmade with mussel populations in Europe and the former SovietUnion. These comparisons include: Population dynamics, growthand mortality rates, ecological tolerances and requirements,dispersal rates and patterns, and ecological impacts. NorthAmerican studies, mostly on the zebra mussel and a few on asecond introduced species, the quagga mussel, Dreissena bugensis,have revealed some similarities and some differences. To dateit appears that North American populations of zebra musselsare similar to European populations in their basic biologicalcharacteristics, population growth and mortality rates, anddispersal mechanisms and rates. Relative to European populationsdifferences have been demonstrated for: (1) individual growthrates; (2) life spans; (3) calcium and pH tolerances and requirements;(4) potential distribution limits; and (5) population densitiesof veligers and adults. In addition, studies on the occurrenceof the two dreissenid species in the Great Lakes are showingdifferences in their modes of life, depth distributions, andgrowth rates. As both species spread throughout North America,comparisons between species and waterbodies will enhance ourability to more effectively control these troublesome species.