The timetable for development of maternal tissues sets the stage for male genomic selection in Betula pendula (Betilaceae)

The influence of the sequence of maternal tissue development in Betula pendula upon the potential for male gamete selection was investigated, and the timing of the fixed abortion of one of the two ovules was determined. We used scanning electronic microscopy, confocal laser scanning microscopy, and blue light microscopy. The stigmas remain fresh throughout male anthesis, and may also last after its end, depending on ambient temperatures. The presence of germinated pollen does not induce stigmatic necrotization, and grains may arrive at different times. The pollen tube tips remain within the stigma base until the end of female anthesis. The ovules will not develop until after necrotization of the stigmas. The pollen tubes thus have a fair start to the ovules, regardless of their different arrival times and of the original positions of the pollen grains at the stigma surface. Therefore, competition among different microgametophytes is possible, in spite of low pollination intensity. Our results indicate that when the first pollen tube penetrates an ovule, this ovule starts to outgrow the other one, and even if the other is also penetrated, its vascular support soon atrophies and the megagametophyte will shrivel. Fertilization of both ovules was never seen in this study.     

EMBRYOLOGICAL STUDY OF HERMINIUM MONORCHIS (ORCHIDACEAE) USING CONFOCAL SCANNING LASER MICROSCOPY

The embryology of Herminium monorchis (Orchidaceae) was studied using confocal scanning laser microscopy (CSLM), a new technique for embryological studies. This technique may contribute new information to plant embryology. Herminium monorchis has a monosporic embryo sac development. The mature embryo sac is 8-nucleate. Two integuments, both 2-layered, are formed, but only the inner takes part in formation of the micropyle. Double fertilization takes place. The primary endosperm nucleus does not divide, but remains alive at least at the 3-celled stage of embryo development. The three antipodals do not show any sign of degeneration at this stage.     

Sealed inside-out and right-side-out plasma membrane vesicles : optimal conditions for formation and separation

Plasma membrane preparations of high purity (about 95%) are easily obtained by partitioning in aqueous polymer two-phase systems. These preparations, however, mainly contain sealed right-side-out (apoplastic side out) vesicles. Part of these vesicles have been turned inside-out by freezing and thawing, and sealed inside-out and right-side-out vesicles subsequently separated by repeating the phase partition step. Increasing the KCI concentration in the freeze/thaw medium as well as increasing the number of freeze/thaw cycles significantly increased the yield of inside-out vesicles. At optimal conditions, 15 to 25% of total plasma membrane protein was recovered as inside-out vesicles, corresponding to 5 to 10 milligrams of protein from 500 grams of sugar beet (Beta vulgaris L.) leaves. Based on enzyme latency, trypsin inhibition of NADH-cytochrome c reductase, and H⁺ pumping capacity, a cross-contamination of about 20% between the two fractions of oppositely oriented vesicles was estimated. Thus, preparations containing about 80% inside-out and 80% right-side-out vesicles, respectively, were obtained. ATPase activity and H⁺ pumping were both completely inhibited by vanadate (K_i ≈ 10 micromolar), indicating that the fractions were completely free from nonplasma membrane ATPases. Furthermore, the polypeptide patterns of the two fractions were close to identical, which shows that the vesicles differed in sidedness only. Thus, preparations of both inside-out and right-side-out plasma membrane vesicles are now available. This permits studies on transport, signal transduction mechanisms, enzyme topology, etc., using plasma membrane vesicles of either orientation.     

Enzyme models: design and selection

There are two approaches to the discovery of enzyme mimics, that is identifying molecules that are able to bind substrate(s) and then catalyze reactions. The first approach, often inspired by enzymes themselves, utilises chemical knowledge and experience to design the catalyst. The other approach is to create a library and select the best host of a transition state analogue of the required reaction.     

Territorial defense against various food competitors in the Tanganyikan benthophagous cichlid <Emphasis Type="Italic">Neolamprologus tetracanthus</Emphasis>

Territorial defense of nonbreeding female Neolamprologus tetracanthus, a shrimp-eating Tanganyikan cichlid, was investigated. Females defended territories (=home ranges, ca. 1m across) against a variety of intruding fishes. Conspecific females were usually attacked outside the territories, heterospecific benthivores (shrimp eaters) and omnivores near the border of the territories, and piscivores, algae and detritus feeders, and herbivores inside the territories. Females used some parts of the sandy substrate in the territories for foraging (foraging areas). Territorial defense prevented most of the conspecific females and benthivores from intruding into the foraging areas. In omnivores, piscivores, and algae and detritus feeders, about half the intruders were repelled from the foraging areas, although herbivores were infrequently repelled in the areas. Soon after removal of the resident females, many food competitors invaded the foraging areas and eagerly devoured prey, suggesting that the territories are maintained for food resource protection from these competitors. Females are likely to discriminate intruding fishes and change their territorial defense primarily on the basis of the degree of dietary overlap, resulting in monofunctional serial territories.     

Avidin related protein 2 shows unique structural and functional features among the avidin protein family

Background  

The chicken avidin gene family consists of avidin and several avidin related genes (AVRs). Of these gene products, avidin is the best characterized and is known for its extremely high affinity for D-biotin, a property that is utilized in numerous modern life science applications. Recently, the AVR genes have been expressed as recombinant proteins, which have shown different biotin-binding properties as compared to avidin.