Prevention of floret abscission for Agapanthus praecox requires an adequate supply of carbohydrate to the developing florets

Vase solutions of 2.5 or 5% (w/v) sucrose markedly reduced the abscission of all open florets and buds on cut Agapanthus praecox stems. Pulsing cut stems with these solutions was not as effective as continuous treatments. Pulse treatments with 10% sucrose for 4–24 h were relatively ineffective at reducing floret and bud abscission but longer pulses of 48 h reduced abscission. The relative ineffectiveness of sucrose pulse treatments appeared to be due to the low water uptake of the stems (1–3 ml/day). Reducing the number of florets and buds on an inflorescence reduced abscission of florets and buds, and increasing stem length from 25 cm to 50 cm decreased bud abscission. This reduction in abscission is possibly due to the increased availability of assimilates for the remaining buds and florets or reduced competition for assimilates. Exogenous ethylene treatments (9 µl/L for up to 24 h) had no effect on abscission, although STS treatment (4 mM, 4 h) significantly reduced floret abscission when stems were held in vase solutions of sucrose. We conclude that postharvest floret abscission in A. praecox is influenced primarily by the availability of assimilates to the developing florets.     

Peroxidase-mediated in vitro metabolism of diethylstilbestrol and structural analogs with different biological activities

The comparative peroxidative metabolism of diethylstilbestrol (DES) and structurally related compounds of different biological activity was investigated in vitro with horseradish peroxidase (HRP) and hydrogen peroxide (H2O2) as a model peroxidase system: UV spectroscopy revealed the formation of p-quinone intermediates in HRP-H2O2 catalyzed incubations of DES, 3',3",5',5"-tetrafluoro-DES (TF-DES) and dimethylstilbestrol (DMS) and the tautomerization of the quinones to their dien compounds, Z,Z-dienestrol (Z,Z-DIES), tetrafluoro-dienestrol (TF-DIES) and dienmestrol (DIMS) respectively, which were characterized by HPLC and GC/MS. Z,Z-DIES, E,E-DIES, TF-DIES and DIMS were subject to further peroxidative metabolism; however, quinone intermediates were not formed in the HRP-H2O2 containing incubations according to UV spectroscopy. Similarly, hexestrol (HES), 4'-O-methyl-DES (M-DES) and 4',4"-O-dimethyl-DES (DM-DES) did not form quinone intermediates; moreover, they showed little or no apparent metabolic conversion under conditions where DES, TF-DES and DMS were readily peroxidized. However, at a 20-fold higher peroxidase concentration HES and M-DES showed metabolic conversion whereas DM-DES did not.     

Macroalgae (seaweeds): industrial resources and their utilization

Summary Seaweeds are distributed widely in all oceans of the world, but exploited in limited areas. These plants have been used for food and as soil conditioners for centuries, with industrial application of extractives a relatively recent innovation generally limited to the more developed areas of the world. There are relatively few species of industrial importance, and these occur in both the red (Rhodophyta) and brown (Phaeophyta) algal divisions.The principal value of phycocolloids is in their gelling and stabilizing properties. Species of red algae may elaborate agar or carrageenan. Both are complex polysaccharides with innumerable structural possibilities, hence physical properties, and phycocolloids from various species can have specific applications. Carrageenans are employed mostly in the food industry, and agars in both the food and pharmaceutical sectors of the economy. Alginates, another family of complex polysaccharides, are obtained from various species of brown algae and are the third major algal gum of commerce. Alginates are used in the food and pharmaceutical industries and have other industrial applications.Issued as NRCC No. 23603.     

Comparative immunogenicity of hepatitis B virus core and E antigens

The nucleocapsid (hepatitis B core Ag (HBcAg] of the hepatitis B virus is a particulate Ag composed of a single polypeptide (p21). Although a non-particulate form of HBcAg designated hepatitis B e Ag (HBeAg) shares significant amino acid identity, the immune responses to these Ag appear to be regulated independently. This report describes the use of recombinant HBcAg and HBeAg to examine and compare murine T cell and B cell recognition of these related Ag. The HBcAg preparation was stable at pH 7.2 and 9.6 and expressed HBc antigenicity. However, the antigenicity of the HBeAg preparation was pH dependent. At pH 9.6 the HBeAg preparation was non-particulate and expressed HBe antigenicity exclusively; however, at pH 7.2 it was particulate and expressed both HBc and HBe antigenicities. Although this "hybrid" particle most likely does not exist naturally, it is a unique research reagent to investigate the interrelationship between HBcAg and HBeAg. HBcAg was significantly more immunogenic in terms of in vivo antibody production as compared to either the non-particulate or particulate forms of HBeAg. Nevertheless, in most murine strains HBcAg and HBeAg were equivalently immunogenic and crossreactive at the level of T cell activation. The disparity between anti-HBc and anti-HBe antibody production is best explained by the observation that HBcAg can function as a T cell-independent Ag whereas HBeAg is T cell dependent even when present within the same particulate structure as HBcAg. Furthermore, HBcAg was shown to function efficiently as an immunologic carrier moiety for the DNP hapten in athymic as well as euthymic mice in contrast to conventional carrier proteins. These results have implications relevant to the human immune responses to HBcAg and HBeAg during infection, and to vaccine development.     

Catechol estrogen formation in mouse uterus

Estrogen 2/4-hydroxylase (ESH) and catechol-O-methyltransferase (COMT) activities in mouse liver and uterus were studied. While 2-hydroxyestradiol (2-OHE2) was the predominant product in the liver, equal amounts of 2- and 4-hydroxyestradiol were produced in the uterus. Two-hydroxyestradiol was the preferred substrate for COMT in both tissues, but the level of this enzyme activity was much less in the mouse uterus (17-fold less). Thus, preferential production of 4-hydroxyestradiol (4-OHE2) in the presence of relatively less deactivation provides a mechanism for the local formation of a more chemically active form of estrogen by uterine tissue.     

Growth of seminal vesicle epithelial cells in serum-free collagen gel culture

Summary Epithelial cells from mouse seminal vesicles were enzymatically dissociated enriched by gradient centrifugation, and maintained in collagen gel cultures with defined (serum-free) media. The epithelial origin of the cells was determined morhologically, immunocytochemically, and biochemically. Cells formed three-dimensional colonies with a lumen in collagen gels. Cell number was increased eight-fold within a 8 to 12-d culture period in a medium supplemented with epidermal growth factor (EGF) (10 ng/ml), insulin (10 μg/ml), transferrin (10 μg/ml), cholera toxin (10 ng/ml), and hydrocortisone (0.1 μg/ml). The cells required eGF and insulin; the growth-promoting effects of these two peptide hormones were optimized by transferrin, cholera toxin, and hydrocortisone. Fetal bovine serum did not support growth; rather, it suppressed the stimulated growth observed in serum-free media. A time-course study revealed that a lag period preceded rapi growth. The collagen gel, serum-free culture provides a powerful tool to study the effects of hormones on proliferation and differentiation of androgen sensitive cells.     

Is flight architecture determined by physical constraints or by natural selection?: the case of the midge Chironomus plumosus

Males of the midge Chironomus plumosus fly solely to mate. They maintain station for long periods in moving air. Females patrol in search of males and, after receiving a spermatophore, fly to oviposition sites. The requirements of flight in males and females are therefore fundamentally different. Females are larger than males, on average, so these differences could stem from scaling rules governing the geometry of space. The same explanation might apply to flight differences within the sexes and even to peculiarities of flight architecture in C. plumosus compared to other flying animals. In other words, might flight design be accounted for entirely by mechanical constraints without recourse to natural selection?
To test this hypothesis, the power output of C. plumosu was measured as size-specific muscle mass. Contrary to expectation, little evidence was found of scaling effects in this measure of power. Despite its being among the smallest of animals to fly, C. plumosus turns out to have the largest mass of flight muscle, relative to body size, yet found among animals. Differences both between C. plumosus and other species and within C. plumosus are, in general, more readily accounted for by the requirements of the mating system within the viscous universe encountered by small flying animals. We conclude that it is natural selection rather than mechanical constraint that is the primary influence determining the architecture of flight in this small animal.     

Persistence of genetic variation in recolonized Tsuga canadensis (Eastern hemlock) populations following historic forest clearance

The recovery of genetic variation in newly recolonized populations is an important concern in forest conservation genetics. We examined the potential recovery of genetic diversity and changes to genetic structure in populations of the wind‐pollinated species Tsuga canadensis that naturally regenerated following the extensive 19th century regional forest clearance for agriculture in west‐central Massachusetts. We genotyped 264 individuals across six microsatellite loci and compared levels and patterns of genetic variation between primary forests (forests that were logged but never cleared) and secondary forests (stands that were recolonized following agricultural abandonment). We found no significant reductions in genetic diversity in secondary forests (A_R = 5.450; H_S = 0.718) compared to primary forests (A_R = 5.742; H_S = 0.730). Moreover, the population genetic differentiation was also not significantly reduced in secondary compared to primary forests, with no significant genetic structure observed among all populations. These results suggest rapid genetic recovery of T. canadensis populations in recolonized forests compared with other late‐successional temperate tree species.