Hydrolysis of Crystalloid Storage Protein in Castor Bean Seed Endosperm During and Following Germination

Hydrolysis of the insoluble crystalloid storage proteins ofcastor bean endosperm during germination released buffer-solublepolypeptides with molecular weights in the presence of sodiumdodecyl sulphate of 30000–40000. These polypeptides appearto be dimers since the addition of 2-mercaptoethanol decreasestheir molecular weights to 15000–22000. Hydrolysis ofthe crystalloid proteins was detected 12–18 h after seedimbibition (HAI), which is before the completion of germination;maximum rates were attained at 30 HAI. During this period, parallelincreases in free amino acids were observed. Hydrolysis of thecrystalloid proteins during early germination was insensitiveto cycloheximide treatment and therefore did not require newlysynthesized proteases. Hydrolysis was effected by proteaseswhich were made in an inactive form during seed developmentand activated upon seed imbibition. Key words: Castor bean, crystalloid storage protein hydrolysis, seed germination, endosperm     

Life history of Xenodexia ctenolepis: implications for life history evolution in the family Poeciliidae

Xenodexia ctenolepis (Hubbs, 1950) is a uniquely asymmetrical species in the fish family Poeciliidae that is endemic to a remote region of Guatemala. In the present study, we describe its life history based on the dissection of 65 adult females from three different collections. We show that it is a livebearer, has superfetation, or the ability to carry multiple litters of young in different stages of development, and has matrotrophy, or placentation, which results in the dry mass of young at birth being three- to four-fold greater than the egg at fertilization. The size distribution of males is non-normal in a fashion that suggests a genetic polymorphism for age and size at maturity. Most phylogenies place Tomeurus gracilis as the sister taxon to the remaining members of the family Poeciliidae. Because Tomeurus is the sole egg-layer in the family, egg-laying is thought to represent the life history of the common ancestor. Because Xenodexia possesses three supposed derived traits (livebearing, superfetation and matrotrophy), this phylogenetic hypothesis suggests that Xenodexia has a highly derived life history with respect to other members of the family. By contrast, the most recent DNA-based phylogeny suggests Xenodexia is the sister taxon to the remainder of the family. If this proves to be true, it suggests that some or all of these life history traits may have been characteristic of the common ancestor to the family, then lost and re-evolved multiple times within the family.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 92 , 77–85.     

Identification and Characterization of the Seed Storage Proteins from Alfalfa (Medicago sativa)

The major seed storage proteins in alfalfa are medicagin (alegumin-like globulin), alfin (a vicilin-like globulin) anda family of Lower Molecular Weight albumins (LMW₁₃). These comprise30%, 10% and 20%, respectively, of the total extractable proteinfrom cotyledons of mature seeds. Alfin is a heterogeneous oligomericprotein (Mr 150 kD) composed of polypeptides ranging in sizefrom Mr 50 to 14 kD (₁,-₆; 50, 38, 32, 20, 16 and 14 kD, respectively).Medicagin is also a high molecular weight oligomeric protein,but requires high concentrations of salt for solubilization.It is comprised of a family of individually distinct subunits,each composed of an acidic polypeptide (A₁–A₉; Mr 49 to39 kD) linked via disulphide bond(s) to a basic polypeptide(B₁, B₂, B₃; Mr 24, 23 and 20 kD, respectively). This pairingis highly specific and two families are recognizable on thebasis of the B polypeptide (B₃ or B₁/B₂). Subunits (M_r 50–65kD) are assembled as trimers (8S) or larger oligomers (12S–15S)in mature seeds. The lower molecular weight albumins (LMW₁–₃)are acidic (pl<6), and consist of sets of disulphide-bondedpolypeptides (Mr 15 and 11 kD). Key words: Medicago sativa, seed storage proteins, alfin, medicagin     

Secondary dormancy (skotodormancy) in seeds of lettuce (Lactuca sativa cv. Grand Rapids) and its release by light, gibberellic acid and benzyladenine

Lettuce seeds (Lactuca sativa L. cv. Grand Rapids) imbibed in darkness at supra-optimal temperatures (23 ± 1°C) develop a secondary dormancy, termed skotodormancy. The seeds first lose their ability to be promoted to germinate by gibberellic acid, and then lose their ability to be promoted by red light. A combination of red light and gibberellic acid will break skotodormancy for longer than either alone, but red light and benzyladenine together are much more effective. Desiccation of skotodormant seeds does not diminish their dormancy. Embryos dissected from skotodormant seeds will germinate, and are as capable of radicle expansion in the osmoticum polyethylene glycol as are newly-imbibed seeds. Hence skotodormancy is a whole seed dormancy and does not reside within the embryo as an inherent block to germination processes, but as an inability to respond to the stimulation of red light or to hormone.     

The Role of Maturation Drying in the Transition from Seed Development to Germination: V. RESPONSES OF THE IMMATURE CASTOR BEAN EMBRYO TO ISOLATION FROM THE WHOLE SEED: A COMPARISON WITH PREMATURE DESICCATION

Kennode, A. R, and Bewley, J. D. 1988. The role of maturationdrying in the transition from seed development to germination.V. Responses of the immature castor bean embryo to isolationfrom the whole seed; a comparison with premature desiccation.—J.exp. Bot. 39: 487–497. Desiccation is an absolute requirement for germination and post-germinativegrowth of whole seeds of the castor bean, whether desiccationis imposed prematurely during development, at 35 d after pollination(DAP) or occurs naturally during late maturation (50–60DAP). Desiccation also plays a direct role in the inductionof post-germinative enzyme synthesis in the cotyledons of embryosin the intact seed; this event is not simply due to the presenceof a growing axis. Isolation of embryos from the developingcastor bean seed at 35 DAP results in both germination and growth,despite the absence of a desiccation event. We have comparedthe metabolic consequences of premature drying of whole seeds(35 DAP) and isolation of the developing 35 DAP embryos. Inboth cases, hydrolytic events involved in the mobilization ofstored protein reserves proceed in a similar manner and mirrorthose events occurring within germinated mature seeds. Thereare differences, however, for post-germinative enzyme (LeuNAaseand isocitrate lyase) production occurs to a lesser extent innon-dried isolated embryos than in those from prematurely dried(35 DAP) whole seeds, or from mature dry (whole) seeds. Desiccationof the 35 DAP whole seed does not alter the subsequent responseof the embryo upon isolation. Thus, while drying does not affectthe metabolism of isolated embryos, it has a profound effecton that of embryos within the intact seed. Tissues surroundingthe embryo in the developing intact seed (viz. the endosperm)maintain its metabolism in a developmental mode and inhibitgermination. This effect of the surrounding tissues can onlybe overcome by drying or by their removal. Key words: Metabolism, isolation, desiccation, embryo, endosperm, castor bean, development, germination     

Annelids from the Lower Devonian Hunsrück Slate (Lower Emsian, Rhenish Massif, Germany)

Abstract:  Four new genera and species of annelid, Hunsrueckochaeta hohensteini , Ewaldips feyi , Crocancistrius lutzi and Scopyrites magnus , are described from the Hunsrück Slate (Lower Emsian) of Germany, as well as new material of Bundenbachochaeta eschenbachensis   Bartels and Blind, 1995 . The specimens preserve details of the appendages and other aspects of the morphology as a result of pyritization. A phylogenetic analysis using the morphological data matrix of Rouse and Fauchald places four of the five genera basal to the Aciculata; the fifth Ewaldips falls within the Scolecida. The diversity of annelids represented in the Hunsrück Slate is similar to that in the other major Palaeozoic Konservat-Lagerstätten that yield them, including the Cambrian Burgess Shale and the Late Carboniferous Mazon Creek biota.     

Vacuolation and Storage Protein Breakdown in the Castor Bean Endosperm following Imbibition

Cytochemical staining of sections prepared for light microscopy,electron microscope sections, and sodium dodecyl sulphate-polyacrylamidegel electrophoresis reveal that, following imbibition, storageproteins are mobilized from the protein bodies of the endospermof castor bean (Ricinus communis L. cv. Hale). This is accompaniedby fusion of protein bodies to form a central vacuole, beforeall the protein is hydrolyzed. Mobilization of the US crystalloidprotein complex and of the 2S albumin fraction commences 2 dafter imbibition and is completed within 2 d. This loss of proteinis accompanied by an increase in activity of three proteolyticenzymes, one carboxypeptidase and two -SH-dependent aminopeptidases.In contrast to the 11S and 2S protein fractions the lectins,located within the protein body, are mobilized only slowly andare present after the other proteins have been completely brokendown. Hence lectins may have a role other than as storage proteins. Key words: Castor bean, Protein breakdown, Storage protein, Lectin, Vacuolation, Seed germination     

The conodont animal

A unique specimen of a small, elongate, soft-bodied animal from the Lower Carboniferous of the Edinburgh district, Scotland, is described. The head expands anteriorly into two lobate structures flanking a central lumen; behind this lies a conodont apparatus, apparently in situ, consisting of an aligned set of ramiform elements followed by a pair of ozarkodiniform elements and one of platform elements. From the morphology of the platform elements the animal has been identified as Clydagnathus? cf. cavusformis. Repeated structures which may represent segments are evident in the posterior part of the trunk, which bears a posterior and a caudal fin, each supported by rays. The animal shows similarities to both chordates and chactognaths, but the evidence supports its assignment to a separate phylum, the Conodonta. The function of the conodonts remains equivocal, but it seems more likely that they served as teeth than as internal supports.