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1.
The breeding cycles of two species of sandy beach whelk (Bulliadigitalis and B. pura) are presented and compared with a thirdspecies (B. rhodostoma). In all three species, egg maturationand copulation occur in spring while summer marks the depositionand spawning of egg capsules. B. digitalis and B. pura migrateoffshore to lay their eggs, the juveniles of both species restrictingthemselves to beyond the breaker zone. Newly hatched snailsof B. rhodostoma appear in the intertidal towards late summer.The discovery of a penis-like structure on females of B. rhodostomais investigated. The pseudopenis was also found on B. pura butnever on B. digitalis. The possibility of a sex-change was eliminatedon the histological investigation of the gonads of a range ofsnails and the examination of sex-ratios over a period of fivemonths. General trends in reproductive behaviour are also discussed. (Received 18 March 1984; 相似文献
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HORST WILKENS 《Biological journal of the Linnean Society. Linnean Society of London》2007,92(2):287-296
Two hypotheses exist to explain ontogenetic eye reduction in Astyanax cave fish: first, after lens induction by the primordial eye cup, the lens plays the role of a central regulator of eye and retina regression or, second, the retina itself is an independent unit of eye development. A comparative study of five blind cave fish populations and their surface sister form was performed to investigate the differences of ontogenetic eye regression between the cave populations during different stages of development. The study revealed that, in addition to the initial formation of smaller primordia, eye regression is also caused during later ontogeny by different relative growth and specific histological characteristics. Whereas the cave fish lens never properly differentiates, the regressive process of the retina is transitorily interrupted by ongoing differentiation. In the newly-discovered Molino cave population, even visual cells with well-organized outer segments develop, which are secondarily reduced at a later ontogenetic stage. This result shows that the retina and lens are independent developmental units within the eye ball. Presumably, the genetic systems responsible for both show independent inheritance, which is also corroborated by hybrids of F 2 -crosses between the cave and surface fish, in which lens and retina development do not correlate. During ontogeny, the eye size differs between the cave populations. In Pachón cave fish, the relatively large eye size correlates with an ancient introgression from a surface population, which may have delayed eye regression. © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 92 , 287–296. 相似文献
3.
Enhanced Superoxide Radical Production in Roots of Zinc-Deficient Plants 总被引:16,自引:1,他引:15
The production of superoxide radical () was studied in roots of cotton (Gossypium hirsutum L. cv. Deltapine15/21), bean (Phaseolus vulgaris L. var. Pr?lude) and tomato(Lycopersicon esculentum L. cv. Super marmande) plants grownin nutrient solution with different Zn concentrations. UsingTiron as a spin-probe, electron spin resonance (ESR) was employedfor the measurements of levels. In the 48 000 g and 140 000 g supernatants of cotton root extracts theamplitude of the Tiron ESR signals reflecting production steeply increased with the appearance of visual Zndeficiency symptoms in the shoots. The changes in the amplitudeof the Tiron ESR signals were closely correlated with an NADPH-dependent generating oxidase activity with a high pH optimum. Increases in NADPH-dependent generation were also found in root extracts of Zn-deficientbean and tomato plants. In all experiments re-supply of Zn todeficient plants for 12 h or 24 h markedly decreased generation. Further, with advancing Zn deficiencyrates of NADPH oxidation increased and the activities of superoxidedismutase (SOD) and catalase decreased. The results suggest that cotton, bean and tomato roots possessan NADPH-dependent generating activity which is affected by the Zn nutritional status of the plants. UnderZn deficiency, enhanced generation and impaired detoxification of Of and H2O2 could lead to elevated levelsof and -derived oxidizing O2 species and thus to increased peroxidation of membrane lipids. Key words: NADPH oxidase, superoxide radical, zinc deficiency 相似文献
4.
Bean (Phaseolus vulgaris L. var. Prelude) plants were grownfor 17 d under controlled environmental conditions with variedZn supply in the nutrient solution. The concentrations of aminoacids; indole-3-acetic acid, IAA; abscisic acid, ABA; isopentenyladenine, I-Ade; isopentenyl adenosine, I-Ado; zeatin, Z; andzeatin riboside, ZR were determined in various shoot fractions. The growth of plants, especially shoot growth, was severelydepressed under conditions of Zn deficiency. Simultaneously,concentrations of soluble protein and chlorophyll decreased,whereas amino acid concentrations increased several-fold. Inthe Zn-deficient plants, the level of IAA in the shoot tipsand young leaves decreased to about 50% of that in Zn-sufficientplants. A similar decrease occurred in the ABA levels of shoottips. In contrast, Zn deficiency was without effect on cytokininlevels in the leaves. Re-supply of Zn to the deficient plantsfor up to 96 h significantly increased shoot growth, solubleprotein, and IAA levels up to the values of Zn-sufficient plants.Simultaneously, the concentration of amino acids dropped tolow levels. The effect of Zn nutritional status on the tryptophanlevel was parallel to that of most of the other amino acids.The results confirm the role of Zn in protein synthesis anddemonstrate that the decrease in IAA level in Zn-deficient plantsis not brought about by impaired synthesis of tryptophan. Itis also unlikely that in Zn-deficient plants the conversionof tryptophan to IAA is specifically inhibited. Key words: Indole-3-acetic acid, tryptophan, zinc deficiency 相似文献
5.
Ethylene-promoted ascorbate peroxidase activity protects plants against hydrogen peroxide, ozone and paraquat 总被引:6,自引:3,他引:3
H. MEHLHORN 《Plant, cell & environment》1990,13(9):971-976
Abstract. In experiments where mung beans ( Vigna radiata L.) and peas ( Pisum sativum L.) have been pre-exposed to ethylene and afterwards treated with ozone, it has been shown that such ethylenepretreated plants may become more resistant to ozone. Further experiments with hydrogen peroxide (H2 O2 ) and the herbicide paraquat suggest that this increased resistance against ozone depends on the stimulation of ascorbate peroxidase activity which provides cells with increased resistance against the formation of H2 O2 which is also formed when plants are fumigated with ozone. These results explain why increased production of ethylene can be observed in plants exposed with ozone or other oxidative stress and clearly demonstrate that in plants, as well as animals, peroxidases protect cells against harmful concentrations of hydroperoxides. 相似文献
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9.
SYNOPSIS. Gamogony of Theileria annulata Dschunkowsky & Luhs occurs within the intestine of nymphs of the tick Hyalomma anatolicum excavatum Koch. After the 5th day post repletionem (p.r.) of the ticks spherical and ovoid parasites were found within the intestinal cells. These stages were thought to represent fertilized macrogametes. These underwent a transformation process leading ultimately to the differentiation of a motile stage, the kinete , which leaves the intestinal cells on the 14th-17th day p.r. and penetrates the alveoles of the salivary glands. The transformation of the stationary into a motile stage takes place by formation of a growing protrusion (= anlage) into an inner, enlarging vacuole. During this process the limiting membrane of the vacuole serves as the outer membrane of the developing motile stage, whereas the 2 inner membranes of its pellicle are newly formed. The steps of this differentiation in T. annulata are compared to the process of ookinete formation in haemosporina. 相似文献
10.
Abstract Segment 9 of male Raphidioptera, comprising tergite, sternite, gonocoxites, gonostyli and gonapophyses, is a benchmark for homologies in the male and female terminalia of the three Neuropterida orders Raphidioptera, Megaloptera and Neuroptera. The segments relating to genitalia are 9, 10 and 11 in males and 7, 8 and 9 in females. Results from holomorphological and recent molecular cladistic analyses of Neuropterida agree in supporting the sister‐group relationships between: (1) the Raphidioptera and the clade Megaloptera + Neuroptera, and (2) the suborder Nevrorthiformia and all other Neuroptera. The main discrepancy between the results of these studies is the nonmonophyly of the suborder Hemerobiiformia in the molecular analysis. The monophyly of the Megaloptera (which has been repeatedly questioned) is further corroborated by a hitherto overlooked ground pattern autapomorphy: the presence of eversible sacs within the complex of the fused gonocoxites 11 in Corydalidae and Sialidae. The recently discovered paired complex of gonocoxites 10 (parameres) in Nipponeurorthus (Nevrorthidae) indicates that the curious apex of sternite 9 of Nevrorthus and Austroneurorthus is the amalgamation of the sclerites of gonocoxites 10 with sternite 9, interpreted as synapomorphic. In the molecular study, the Nevrorthidae, Sisyridae and Osmylidae branch off in consecutive splitting events, a result that is supported by the analysis of male genital sclerites reported here. Extraordinary parallel apomorphies (e.g. excessive enlargement and modification of gonocoxites 10 ending in a thread‐like ‘penisfilum’) in derived representatives of Coniopterygidae, Berothidae, Rhachiberothidae and Mantispidae corroborate the dilarid clade of the morphological analysis and leads us to hypothesize a sister‐group relationship of the Coniopterygidae with the dilarid clade. A re‐interpretation of the tignum of Chrysopidae as gonocoxites 11 means that the structure previously called the gonarcus represents the fused gonocoxites 9. In Hemerobiidae, the corresponding sclerite is consequently also homologized as fused gonocoxites 9. The enlargement of the lateral wings of the gonocoxites in both families is interpreted as a synapomorphy. Excessive enlargement of gonostyli 11 in the Polystoechotid clade and Myrmeleontiformia supports a sister‐group relationship of these two clades. The occurrence of certain serial homologues of female genitalia structures (gonocoxites and gonapophyses), such as the digitiform processus together with the flat appendices in segment 8 of certain Myrmeleontidae, or the wart‐like processus together with the flat circular sclerites in segment 7 of certain Berothidae, as well as the presence of gonocoxites 8 as pseudosternites in certain Nemopteridae and Coniopterygidae, are probably character reversals. The digitiform processus of tergite 9 (pseudogonocoxites) in Rhachiberothidae and Austroberothella (Berothidae) are either independently developed acquisitions with a function in oviposition, or are homologous sclerites, possibly of epipleurite origin. 相似文献