Changes in responsiveness to ethylene and gibberellin during corolla expansion ofIpomoea nil

Corolla expansion inIpomoea nil appears to be triggered by changes in gibberellin concentration and ethylene production during development. We investigated the role of responsiveness to GA and ethylene in corolla expansion. The effects of growth regulators applied in vitro were measured as a change in area of corolla segments from younger (15–17 mm) and older (18–20 mm) whole corollas. Applied gibberellic acid (GA₃) significantly (p < 0.05) promoted growth in the younger segments but was less effective in the older segments. Moreover, applications of the GA biosynthesis inhibitors, PP333 (paclobutrazol) AMO₁₆₁₈ (2-isopropyl-4-dimethylamino-5-methylphenyl-1-piperidinecarboxylate methyl chloride), chlorocholine chloride, and tetcyclasis had little effect on younger segments but inhibited growth of older segments. The older corollas have apparently synthesized and accumulated enough GA-like substances to become less responsive to additional applied GA₃. The amount of growth induced by applied or endogenous GA depended on the amount of ethylene simultaneously produced in the tissue. The younger corollas rapidly produced ethylene from endogenous 1-aminocyclopropane-1-carboxylic acid (ACC) and did not respond to applied ACC whereas the older corollas naturally produced much less ethylene and were significantly (p < 0.05) inhibited by applied ACC. When ethylene production was inhibited by applying aminoethoxyvinylglycine (AVG), growth was promoted in all segments. However, only the growth of the younger segments was further stimulated by simultaneously applied AVG and GA₃ over the GA₃ control. Thus the differential responses of segments from 15- to 20-mm long corollas to applied growth regulators reflect developmental changes in responsiveness of the developing corolla. The change in responsiveness is attributed in part to the changes in production of endogenous growth regulators and to the effect of one endogenous plant growth regulator (PGR) on the responsiveness of the corolla to another PGR.     

Guidelines for selective radiological assessment of inversion ankle injuries.

A prospective study was performed to establish definitive guidelines for selective use of radiography in the assessment of inversion ankle injuries. Five hundred patients were included, representing 3.2% of the workload of the department during the study period. There were 379 soft tissue injuries, 56 malleolar fractures, 40 avulsion fractures, 21 fractures at the base of the fifth metatarsal, and four calcaneal fractures. Multiple logistic regression identified distal fibular tenderness, age, and ability to bear weight as the most important clinical variables in predicting important fractures (p less than 0.001). A policy of requesting x ray examination of only those patients with distal fibular tenderness or inability to bear weight or aged over 60, with a further proviso that no foot radiographs should be obtained, would produce a 60% reduction in ankle radiography in this centre without detriment to patient care.     

Bone mechanical properties after exercise training in young and old rats

The effects of a 10-wk training regimen on the mechanical properties of the femur and humerus were evaluated in 2.5- and 25-mo-old Fischer 344 female rats. The rats trained on a rodent treadmill 5 days/wk for 10 wk. Duration, grade, and speed increased until the rats maintained 1 h/day at 15% grade and either 15 m/min (old rats) or 36 m/min (young rats). Excised bones were mechanically tested with a 3-point flexure test for mechanical properties of force, stress, and strain. Fat-free dry weight (FFW) and moment of inertia were also obtained. With aging, similar increases were observed in both the femur and humerus for FFW, moment of inertia, and force. Ultimate stress was reduced in the senescent femur while strain was elevated; a similar but nonsignificant trend was observed in the humerus. Irrespective of age, training increased FFW in the femur and, to a lesser degree, in the humerus. Breaking force was elevated for both bones after training. In young and old bones, the training-induced differences in bone mass and force were similar, despite differences in training intensity. In the old trained rats, femur ultimate stress was greater than that in control rat femurs and similar to that in young rat femurs. The results of the present study indicate that training effects were not limited by age.     

Excess amino acid polymorphism in mitochondrial DNA: contrasts among genes from Drosophila, mice, and humans

Recent studies of mitochondrial DNA (mtDNA) variation in mammals and Drosophila have shown an excess of amino acid variation within species (replacement polymorphism) relative to the number of silent and replacement differences fixed between species. To examine further this pattern of nonneutral mtDNA evolution, we present sequence data for the ND3 and ND5 genes from 59 lines of Drosophila melanogaster and 29 lines of D. simulans. Of interest are the frequency spectra of silent and replacement polymorphisms, and potential variation among genes and taxa in the departures from neutral expectations. The Drosophila ND3 and ND5 data show no significant excess of replacement polymorphism using the McDonald-Kreitman test. These data are in contrast to significant departures from neutrality for the ND3 gene in mammals and other genes in Drosophila mtDNA (cytochrome b and ATPase 6). Pooled across genes, however, both Drosophila and human mtDNA show very significant excesses of amino acid polymorphism. Silent polymorphisms at ND5 show a significantly higher variance in frequency than replacement polymorphisms, and the latter show a significant skew toward low frequencies (Tajima's D = -1.954). These patterns are interpreted in light of the nearly neutral theory where mildly deleterious amino acid haplotypes are observed as ephemeral variants within species but do not contribute to divergence. The patterns of polymorphism and divergence at charge-altering amino acid sites are presented for the Drosophila ND5 gene to examine the evolution of functionally distinct mutations. Excess charge-altering polymorphism is observed at the carboxyl terminal and excess charge-altering divergence is detected at the amino terminal. While the mildly deleterious model fits as a net effect in the evolution of nonrecombining mitochondrial genomes, these data suggest that opposing evolutionary pressures may act on different regions of mitochondrial genes and genomes.      

Characterization of the T, L, I, S, M and P cell surface (immobilization) antigens of Tetrahymena thermophila: molecular weights, isoforms, and cross-reactivity of antisera.

In the ciliate protist Tetrahymena thermophila the L, H, T, I, S, M and P cell surface proteins (immobilization antigens) are expressed under different conditions of temperature (L, H, T), culture media (I, S), and mutant genotype (M, P). Immunoblot and autoradiographic studies using antisera to purified protein show that the molecular weights of these proteins range from 25,000 to 59,000. The H, T, S, M and P antigens are recognized as single polypeptides, whereas L, I, and one allelic form of T each appear to consist of a family of polypeptides. Although antisera are specific in immobilization and immunofluorescence assays of surface protein in living cells, cross-reactivity is seen with denatured protein on immunoblots. It is hypothesized that the surface protein genes are organized into families of evolutionarily related isoloci.