PROXIMATE AND ULTIMATE SOURCES OF WITHIN-INDIVIDUAL VARIATION IN SEED MASS IN PRUNELLA VULGARIS (LAMIACEAE)

Substantial variation in seed mass within individual seed parents is at odds with predictions of models for the evolution of optimum offspring size and with empirical observations of directional selection on seed mass. To elucidate the ultimate causes of this variation, I examined several proximal sources of within-individual variation in seed mass in the perennial herb Prunella vulgaris. Position of inflorescence, position of flower within an inflorescence, date of anthesis, and number of seeds produced per flower all explained some within-individual variation in seed mass. Hand pollination in the field failed to reveal any effect of pollen source (self pollen or outcross pollen) on seed mass. My results, in conjunction with those from studies of selection on seed mass in P. vulgaris, do not support hypotheses that within-individual variation in seed mass is favored by the pattern of natural selection on seed mass. Rather, the results suggest that seed parents are not capable of producing a uniform seed crop in the face of changes in resource availability in the course of a season. The inability to produce a uniform seed crop may persist because of selection for variability in traits correlated with seed mass or because of a true constraint on the evolution of uniform offspring size.     

Leukotriene B4 binding to human neutrophils

[³H] Leukotriene B₄ (LTB₄) binds concentration dependency to intact human polymorophonuclear leukocytes (PMN's). The binding is saturable, reaches equilibrium in 10 min at 4°C, and is readily reversible. Mathematical modeling analysis reveals biphasic binding of [³H] LTB₄ indicating two discrete populations of binding sites. The high affinity binding sites have a dissociation constant of 0.46 × 10⁻⁹M and B_max of 1.96 × 10⁴ sites per neutrophil; the low affinity binding sites have a dissociation constant of 541 × 10⁻⁹M and a B_max of 45.6 × 10⁴ sites per neutrophil. Competitive binding experiments with structural analogues of LTB₄ demonstrate that the interaction between LTB₄ and the binding site is stereospecific, and correlates with the relative biological activity of the analogs. At 25°C[³H] LTB₄ is rapidly dissociated from the binding site and metabolized to 20-OH and 20-COOH-LTB₄. Purification of neutrophils in the presence of 5-lipoxygenase inhibitors significantly increases specific [³H] LTB₄ binding, suggesting that LTB₄ is biosynthesized during the purification procedure. These data suggest that stereospecific binding and metabolism of LTB₄ in neutrophils are tightly coupled processes.     

Localization of the nucleolar organizer by computer-aided analysis of a variant no. 21 in a human isolate

Summary A variant chromosome no. 21 consisting of two stalks and two satellites in tandem was detected during a survey of a human isolate. The variant segregated in three generations of a large kindred. One male had the variant no. 21, a metacentric Y, and a 47, XXY complement; however, no other evidence of chromosomal nondisjunction was found. Computer-aided analysis of sequentially stained variant no. 21 chromosomes indicated that silver-stained material corresponded to the proximal stalk region (as defined defined by Giemsa). These data support the hypothesis that human nucleolar organizers are localized to the stalks of acrocentric chromosomes.