The effect of nectar production on neighborhood size

Summary Bumblebee foraging behavior was observed on two plant species with similar floral and inflorescence structures. One species produces nectar while the other does not. Bees, upon visiting nectar producing flowers tend to empty them of nectar and by frequently moving between close neighbors, create a patchily distributed resource base. Bees maximize their foraging efficiency in such an environment by using an area-restricted searching behavior and flying distances inversely correlated with the quality of reward received. Pollen collecting bumblebees do not create a patchy environment and maximize their foraging efficiency by more consistently moving shorter distances. Pollen collecting bumblebees are significantly more likely to revisit flowers and to visit more flowers per inflorescence than are nectar gathering bumblebees. These differences in foraging behavior increase the neighborhood size for nectar producing species and make it increasingly unlikely that random drift will be a dominant mode of evolution in populations of these species.     

Responses to moisture stress in male and female plants of Rumex acetosella L. (Polygonaceae)

Summary Male and female plants of Rumex acetosella were grown on a moisture gradient to measure possible differences in the drought tolerance of the sexes. The growth of both sexes declined under water stress but males were significantly more drought tolerant. This could not be explained by greater water use efficiency in the male plants; measured rates of both photosynthesis and leaf conductance did not differ significantly between the sexes. Multiple discriminant analysis showed that the sexes differed at all moisture regimes in their overall patterns of biomass allocation. Males had proportionately greater investment in root and leaf tissue which could explain their growth advantage over females under water stress. Despite essentially equal water use efficiencies, on a per plant basis males, with more leaf and root biomass, could fix more carbon and more rapidly exploit the local water resource than females. Thus the pattern of biomass allocation rather than intrinsic physiological differences appears to explain the greater drought tolerance of male plants of Rumex acetosella.     

Analysis of histidine-containing dipeptides, polyamines, and related amino acids by high-performance liquid chromatography: application to guinea pig brain.

A procedure is described for coupling wheat germ agglutinin to cyanogen bromide-activated Sepharose to yield a lectin affinity column of high capacity. Covalent linkage of the lectin to the insoluble matrix is carried out in the presence of a mixture of β-1,4-linked N-acetylglucosamine oligosaccharides prepared from chitin. The lectin-affinity column specifically recognizes glycoproteins containing N-acetylglucosamine residues with the capacity of binding 0.6–1.0 mg of ovomucoid per milliliter of gel. The affinity column is stable (as determined by ovomucoid binding) and shows little loss in binding capacity or specificity after repeated usage. Important characteristics for the use of this column to purify glycoproteins are described.     

In vivo measurements of the viscoelasticity of the human vitreous humor.

A point of source of light against a dark background is perceived by the human retina as a point image enhanced by off-axis points (rays if the source is polychromatic) of light scattered from objects along the optic axis. As a consequence of movement of the vitreous humor, scattering centers imbedded there impart of this scattering pattern a corresponding movement. A method has been devised to give the vitreous humor reproducible initial conditions and to record the observed relaxation of the scattering pattern to its new rest position. The vitreous humor is found to be overdamped, and the heretofore unreported shear elastic modulus has been determined. A striking gravitational effect is revealed by comparing observations along a horizontal optic axis with ones along a vertical optic axis. For the former, gravitational torque is found to dominate the elastic torque. The reason nature has developed a slow-responding gravitational sensor in the vitreous humor is not clear.     

Identification of Traumatin, a Wound Hormone, as 12-Oxo-trans-10-dodecenoic Acid

12-Oxo-trans-10-dodecenoic acid (trans-10-ODA) is an oxidation product of polyunsaturated fatty acids in plant tissues. The structural similarity of trans-10-ODA and traumatic acid, a compound considered to be a wound hormone, suggested that trans-10-ODA might be a precursor of traumatic acid. Both trans-10-ODA and traumatic acid were active in the Wehnelt bean assay. The results were more consistent with trans-10-ODA than with traumatic acid. Cucumber (Cucumis sativus L. var. National Pickling) hypocotyls also showed a growth increase following treatment with trans-10-ODA, which suggested that trans-10-ODA has a more general influence on plant development than previously ascribed to traumatic acid.     

Interactions among nickel,copper, and iron in rats

In two fully-crossed, three-way, two-by-three-by-three, factorially arranged experiments, female weanling rats were fed a basal diet supplemented with iron at 15 and 45 μg/g, nickel at 0, 5, and 50 μg/g, and copper at either 0, 0.5, and 5 μ/g (Expt. 1) or 0, 0.25, and 12 μg/g (Expt. 2) A gram of basal diet contained in Expt. 1 approximately 16 ng of nickel, 2.3 μg of iron, and 0.47 μg of copper; and in Expt. 2, 20 ng of nickel, 1.3 μg of iron, and 0.39 μg of copper. Expt. 1 was terminated at 11 weeks, and Expt. 2 at 8 weeks because, at those times, some rats fed no supplemental copper and the high level of nickel began to lose weight, or die from heart rupture. The findings demonstrated that relationships are complex among nickel, copper, and iron. Nickel interacted with copper and this interaction was influenced by dietary iron. Signs of copper deficiency were more severe when nickel was supplemented to the diet provided that copper deprivation was neither very severe nor mild. Iron deprivation apparently enhanced the antagonism by exacerbating copper deficiency. Signs of copper deficiency that were made more severe by nickel supplementation were depressed weight gain (Expt. 2), hematocrit (Expt. 1), hemoglobin, and plasma alkaline phosphatase activity; and elevated ratios of heart wt/body wt, kidney wt/body wt, and liver wt/body wt. Because nickel and copper have similar physical and chemical properties, the interactions between those two elements were probably the result, of isomorphous replacement of copper by nickel at various functional sites that interfered with some biological processes.     

Multiple forms of ACTH biological activity in the pars intermedia of the rat adenohypophysis.

Acid extracts of a) acutely dispersed rat pars intermedia (PI) cells, b) media after incubation of PI cells, c) whole nervosa-intermedia, and d) whole pars distalis, were chromatographed on Sephadex G-50 Fine in 1% acetic acid. Three peaks of ACTH biological activity were resolved in all four extracts. Peak I eluted in the void volume of the column, peak III co-eluted with synthetic ACTH^1–39, and peak II eluted in an intermediate position. The predominant ACTH activity derived from the PI tissue was peak I, amounting to over 70% of the total ACTH activity present in that lobe. The positions of PI peaks I and II remained unaltered after rechromatography as well as after treatment with and chromatography in 8 M urea. However, peak I of PI ACTH was further resolved into two separate peaks by chromatography on Sephadex G-100 SF. Thus pars intermedia ACTH activity appears to be composed of four separate entities, with the predominant forms being larger than ACTH^1–39.     

Rapid release of bound glucose-6-phosphate dehydrogenase by growth factors. Correlation with increased enzymatic activity

Epidermal growth factor (EGF), a mitogen for renal proximal tubule cells, activated the hexose monophosphate (HMP) shunt in renal proximal tubule cells (Stanton, R. C., and Seifter, J. L. (1988) Am. J. Physiol. 254, C267-C271). We therefore evaluated the effect of EGF on the HMP shunt enzymes glucose 6-phosphate dehydrogenase (G6PD, the rate-limiting enzyme) and 6-phosphogluconate dehydrogenase. Rat renal cortical cells (RCC) were incubated with either EGF or platelet-derived growth factor (PDGF) and then assayed for G6PD and 6-phosphogluconate dehydrogenase activities. EGF and PDGF increased G6PD activity by 25 and 27% respectively. Although phorbol myristate acetate (PMA), ionomycin, PMA + ionomycin, and 8-bromo-cyclic AMP had no significant effect on the activity, a 5-min preincubation with PMA potentiated the activation of G6PD by PDGF. Growth factor activation of G6PD was also seen in a fibroblast and epithelial cell line. None of the agents affected 6-phosphogluconate dehydrogenase activity in the RCC or in the cell lines. Further exploration into a possible mechanism for G6PD activation revealed that growth factors caused release of G6PD from a structural element within the cell. Streptolysin O permeabilization of RCC did not cause significant release of G6PD. However, within 1 min of addition of EGF or PDGF to permeabilized cells, G6PD was released into the cell supernatant. The nonhydrolyzable analog of GTP, guanosine 5'-O-(thiotriphosphate), caused a similar release of G6PD. Preincubation with pertussis toxin or guanyl-5'-yl thiophosphate inhibited the PDGF but not the EGF effect. Although the data do not establish a definitive proof linking G6PD release and G6PD activation, these results suggest that they are related. Thus, growth factor stimulation of the HMP shunt likely occurs by a novel mechanism associated with release of bound G6PD.     

Oxidatively fragmented phosphatidylcholines activate human neutrophils through the receptor for platelet-activating factor.

Platelet-activating factor (PAF, 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine) activates neutrophils (polymorphonuclear leukocytes, PMN) through a receptor that specifically recognizes short sn-2 residues. We oxidized synthetic [2-arachidonoyl]phosphatidylcholine to fragment and shorten the sn-2 residue, and then examined the phospholipid products for the ability to stimulate PMN. 1-Palmitoyl-2-arachidonoyl-sn-glycero-3-phosphocholine was fragmented by ozonolysis to 1-palmitoyl-2-(5-oxovaleroyl)-sn-glycero-3-phosphocholine. This phospholipid activated human neutrophils at submicromolar concentrations, and is effects were inhibited by specific PAF receptor antagonists WEB2086, L659,989, and CV3988. 1-Palmitoyl-2-arachidonoyl-sn-glycero-3-phosphocholine next was fragmented by an uncontrolled free radical-catalyzed reaction: it was treated with soybean lipoxygenase to form its sn-2 15-hydroperoxy derivative (which did not activate neutrophils) and then allowed to oxidize under air. The secondary oxidation resulted in the formation of numerous fragmented phospholipids (Stremler, K. E., Stafforini, D. M., Prescott, S. M., and McIntyre, T. M. (1991) J. Biol. Chem. 266, 11095-11103), some of which activated PMN. Hydrolysis of sn-2 residues with phospholipase A2 destroyed biologic activity, as did hydrolysis with PAF acetylhydrolase. PAF acetylhydrolase is specific for short or intermediate length sn-2 residues and does not hydrolyze the starting material (Stremler, K. E., Stafforini, D. M., Prescott, S. M., and McIntyre, T. M. (1991) J. Biol. Chem. 266, 11095-11103). Neutrophil activation was completely blocked by L659,989, a specific PAF receptor antagonist. We conclude that diacylphosphatidylcholines containing an sn-2 polyunsaturated fatty acyl residue can be oxidatively fragmented to species with sn-2 residues short enough to activate the PAF receptor of neutrophils. This suggests a new mechanism for the appearance of biologically active phospholipids, and shows that PAF receptor antagonists block the action of both PAF and these PAF-like lipids.     

Controlling vitrification of petunia in vitro

Summary Nodal segments from in vitro culturedPetunia hybrida were grown under varying cultural conditions. The origin of nodal explants influenced vitrification. Basal segments formed a higher percentage of vitreous shoots than did the upper nodes. A method was developed for including polyethylene glycol with Gelrite to obtain gelled media of varying water potentials. Media water potential from −0.31 to −1.2 MPa had no effect on controlling the level of vitrification. Gelrite promoted vitrification but GIBCO agar, alone or in combination with Gelrite, reduced its occurrence. Lowering media NH₄ content reduced vitrification, whereas sealing culture vessels with parafilm increased it. As it is now possible to control normal and vitreous plant development inPetunia, this can be used as a model system for studying the physiology and biochemistry of this developmental abnormality.