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Biomedical subjects

B F Wilson

Publications and source records attributed to B F Wilson.

13 recordsLinked to original sources
PubMed2000

Apical control of branch growth and angle in woody plants.

Apical control is the inhibition of a lateral branch growth by shoots above it (distal shoots). If the distal shoots are cut off to remove apical control, the lateral branch can grow larger and may bend upwards. Apical control starts when new lateral buds grow after passing through a period of dormancy. Buds initially break and produce leaves, then apical control is exerted and the lower (proximal) laterals stop growing. Apical control also inhibits growth of large, old branches. Gravimorphism and restricted water and nutrient transport can inhibit branch growth, but they are not primary mechanisms of apical control. Apical control may reduce branch photosynthesis. Under apical control allocation of branch-produced assimilate to the stem is relatively high, so low assimilates in the branch may limit branch growth even though hormone levels are adequate for growth. Hormones appear to be involved in apical control, but it is not known how. One role of hormones may be to maintain the strength of the stem sink for branch-produced assimilate. Upward bending of a woody branch after release from apical control requires both new wood production and production of wood cells that can generate an upward bending moment. Apical control inhibits radial growth of branches and, in some species, may regulate the production of wood with an upward bending moment.

Journal Article↗
PubMed1997

Response to stem bending in forest shrubs: stem or shoot reorientation and shoot release.

Shrubs in the forest understory may be bent by their own weight or by overstory debris. To maintain height growth they must respond to bending by vertical growth of new shoots, reorientation of older axes, or by releasing preventitious buds to form epicormic shoots. I tested for these responses in Ilex verticillata L., Cornus amomum Mill., Gaylussacia baccata (Wang.) K. Koch, Viburnum cassinoides L., Hamamelis virginiana L., and Kalmia latifolia L. For each species, I removed potentially supporting vegetation adjacent to 20 stems, left 10 stems untreated to test for bending by self weight, and bent the remaining 10 stems to 45 degrees to simulate effects of fallen debris. Stem angles and curvatures were measured from before leaf out until just before leaf fall to detect either sagging from self weight or upward bending from tension wood action. Control stems initially leaned out of vertical and five of six species sagged further into a cantilever form. Several control stems failed and bent to the ground. Stems of H. virginiana, I. verticillata, and C. amomum formed tension wood, but only the first two species bent upward. Viburnum cassinoides, G. baccata, and K. latifolia formed no tension wood and sagged further down after being bent. Epicormic shoots formed with varying frequencies in all species except K. latifolia. Epicormic shoots were the major response in C. amomum, V. cassinoides, and G. baccata. New terminal shoots on bent stems recovered toward vertical in I. verticillata and K. latifolia. Negative gravitropic response of shoots was the only recovery mechanism for K. latifolia.

Forestry↗
PubMed1992

Remarriages: a demographic profile.

"This article presents descriptive statistics for remarriages [in the United States] according to the combined marital histories of brides and grooms. In 1988, 745,000 divorced men and 748,000 divorced women remarried. For each sex, 61% married divorced, 35% married single, and 4% married widowed partners. On average, the grooms were 39 and the brides were 35 years of age, but those who married single partners were younger (35 and 31, respectively) and better educated than average. In 1988, 72,000 widowed men and 77,000 widowed women remarried, at ages 61 and 53. They married widowed or divorced partners in similar proportions. By 1988, husbands and wives who jointly remarried at ages 25 to 44 in 1972 had lower divorce levels than did those who were first married as teenagers. This indicates that marrying at a young age was a stronger determinant of divorce than was a previous marriage of either or both spouses."

Age Factors↗
PubMed1991

Relationship between in vitro relaxation of the costo-uterine smooth muscle and mesovarial leiomyoma formation in vivo by beta-receptor agonists.

The three beta-agonists, salbutamol, ritodrine, and terbutaline have been shown to possess differing potentials to induce leiomyomas in rat costo-uterine muscle following chronic exposure (salbutamol greater than terbutaline greater than ritodrine). It has been suggested that the potential to induce leiomyomas is related to the relaxant properties of these agonists in the costo-uterine muscle. In order to test this hypothesis, the potencies of salbutamol, terbutaline, and ritodrine were compared to isoproterenol and norepinephrine in vitro in the rat costo-uterine smooth muscle, a beta 2-adrenergic receptor rich tissue. All compounds produced relaxation of potassium chloride (KCl) contracted costo-uterine smooth muscle. Significant differences in potency were observed, with isoproterenol being the most potent, followed in rank order by salbutamol, terbutaline and ritodrine. The relative potency of the non-selective beta-blocker propranolol in inhibiting the agonist mediated relaxant activity was similar for all agonists examined, indicative of interactions at the same receptor site (Tallarida and Jacob 1979). When tested for beta-agonist activity in the guinea pig atria, salbutamol and ritodrine were less potent in these tissues compared to the costo-uterine muscle. In summary, the in vitro pharmacological potency of salbutamol, terbutaline and ritodrine correlated with the potential to induce leiomyoma formation in rat costo-uterine muscle following chronic exposure to the respective beta-agonists. These results indicate that the isolated rat costo-uterine muscle is a sensitive model for comparing the potency of beta-agonists, and may assist in establishing the risk of costo-uterine leiomyoma formation in chronic rat studies relative to agents such as salbutamol.

Adrenergic beta-Agonists↗
PubMed1989

Distribution of endogenous indole-3-acetic Acid and compression wood formation in reoriented branches of douglas-fir.

Five-year-old segments of intact 7-year-old branches of Douglas-fir (Pseudotsuga meziesii [Mirb.] Franco) were reoriented to determine the relation between indole-3-acetic acid (IAA) and the formation of compression wood. Eight branches per treatment were either left at their original angle (mean of 69 degrees , the control), or bent proximal to the segment to reorient it up or down 30 degrees . Differentiating xylem tissue from the upper and lower sides of each segment was collected and extracted separately for IAA analysis by in-line fluorescence detection of free IAA and IAA methyl ester after sequential C(16) reversed-phase high performance liquid chromatography. The IAA methyl ester was confirmed by gas chromatography-mass spectroscopy. Compression wood formed on the upper side of branches reoriented up and on the lower side of controls or branches reoriented down. IAA was present in all samples. The difference in IAA concentration between upper and lower sides was either not correlated, or negatively correlated in segments reoriented down, with both the occurrence of compression wood and the rate of new tracheid production. Mean concentrations for whole branch segments were not affected by the treatments, regardless of whether IAA concentrations were expressed on a surface area, weight, or cell basis.

Journal Article↗
PubMed1981

Apical control of branch movements in white pine: biological aspects.

Two-year-old branches on control trees (Pinus strobus L.) were compared through a season with branches on trees stem-girdled just above, or below, the branch whorl. All branches first sagged down for 20 days and then moved up for 40 days. Then, control branches reversed and moved back down while branches in both girdle treatments continued to move up. Movement reversal correlated with cessation of both elongation and diameter growth in control branches. Diameter growth continued in branches of girdled trees. Control branches continued to stiffen even after diameter growth stopped. Differences in movements due to girdling are from compression wood formed after cessation of branch elongation. Apical control stops cambial activity and compression wood formation in branches after branch elongation ceases, allowing photosynthate produced in the branch to move to the stem. Control branches bend down from increasing self-weight after cambial activity ceases.

Journal Article↗
PubMed1973

Mechanics of the Compression Wood Response: II. On the Location, Action, and Distribution of Compression Wood Formation.

A new method for simulation of cross-sectional growth provided detailed information on the location of normal wood and compression wood increments in two tilted white pine (Pinus strobus L.) leaders. These data were combined with data on stiffness, slope, and curvature changes over a 16-week period to make the mechanical analysis. The location of compression wood changed from the under side to a flank side and then to the upper side of the leader as the geotropic stimulus decreased, owing to compression wood action. Its location shifted back to a flank side when the direction of movement of the leader reversed. A model for this action, based on elongation strains, was developed and predicted the observed curvature changes with elongation strains of 0.3 to 0.5%, or a maximal compressive stress of 60 to 300 kilograms per square centimeter. After tilting, new wood formation was distributed so as to maintain consistent strain levels along the leaders in bending under gravitational loads. The computed effective elastic moduli were about the same for the two leaders throughout the season.

Journal Article↗
PubMed1970

Mechanics of the compression wood response: I. Preliminary analyses.

Righting of two tilted white pine (Pinus strobus L.) stem leaders by compression wood formation was followed for 16 weeks. The natural curves and three deflection curves under added end loads were determined from weekly field photographs. Data for self-loading and cross sectional diameters were interpolated from original estimated and final measurements. A mechanical-mathematical model was developed to predict curves under zero gravity for each stem each week. The model estimated stiffness of the leaders independently for each week, and the stiffnesses were consistent throughout the experiment. A second model was developed to simulate the deflection curves assumed when the zero gravity curves were subjected to different end loads. These predicted curves were nearly identical to the observed curves from the photographs, thus verifying the assumptions in the first model. Data from this study will be used to investigate the mechanical aspects of compression wood induction and action as the stem is bent upward toward the vertical.

Journal Article↗