Carbon integration in Plantago aristata (Plantaginaceae): the reproductive effects of defoliation

Patterns of carbon integration in aclonal species are poorly understood in spite of their potential to influence individual fitness. To provide more information about these patterns, we performed a defoliation experiment with P. aristata. We examined, at the metameric level, the reproductive responses to the removal of the major carbon sources within metamers. Bracts on marked reproductive spikes and leaves subtending these spikes were removed at three stages of reproductive maturity: spike elongation, flowering, and fruiting. Spike dry weight and length, capsule number, seeds per capsule, and seed weight were measured. We tested the hypothesis that seed weight would respond least to defoliation. We also performed a complementary ¹⁴C translocation experiment to measure the amount of radioactive carbon moving into the marked spikes from outside the metamer. Defoliation depressed all components of reproduction within marked spikes, and little ¹⁴C was translocated from outside the metamer into the reproductive spikes, even those that were defoliated. Both results support the view that reproductive metamers in this species are largely autonomous with respect to their carbon budget. Defoliation during spike elongation most depressed reproduction, and bract removal depressed reproduction more than did leaf removal. The data suggest that bracts compensate for leaf removal by increasing their photosynthetic rate; however, the ability to compensate differs among plant populations. Of all the reproductive components, seed weight was least affected by defoliation. The data show, however, that the time of defoliation relative to reproductive development influences which reproductive components are affected.     

Genetic transformation of the Lyme disease agent Borrelia burgdorferi with coumarin-resistant gyrB.

No useful method to genetically manipulate Borrelia burgdorferi, the causative agent of Lyme disease, has been developed previously. We have used resistance to the coumarin antibiotic coumermycin A1, an inhibitor of DNA gyrase, as a genetic marker to monitor the transformation of B. burgdorferi by electroporation. Introduction of site-directed mutations into the gyrB gene demonstrated that transformation was successful, provided evidence that homologous recombination occurs on the chromosome, and established that mutations at Arg-133 of DNA gyrase B confer coumermycin A1 resistance in B. burgdorferi. The coumermycin A1-resistant gyrB marker and genetic transformation can now be applied toward dissecting the physiology and pathogenesis of the Lyme disease agent on a molecular genetic level.     

Abundance of airborne Penicillium CFU in relation to urbanization in Mexico City.

Air was sampled simultaneously at three localities in Mexico City differing in urbanization index and air pollution level on 22 days during a period covering both dry and rainy seasons. An Andersen two-stage microbial sampler was used for 15 min at 28 liters min-1 to isolate culturable fungi on malt extract agar. After exposure, plates were incubated at 25 degrees C for 48 to 72 h before colonies were counted and identified to give concentrations of total fungal spores and of Penicillium spp., expressed as CFU per cubic meter of air. Total fungi numbered 91 to 602 CFU m-3 in Tlalpan Borough (southern area), 40 to 264 CFU m-3 in Cuauhtémoc Borough (downtown), and 26 to 495 CFU m-3 in Gustavo A. Madero Borough (northern area). Although Penicillium spp. were the second most frequently isolated fungal genus, concentrations were small, with a maximum of only 133 CFU m-3. Twice as many colonies were isolated in the southern area, with an urbanization index of 0.25 (arithmetic mean, 41 CFU m-3), as at other sampling stations with greater urbanization indices (arithmetic means, 19 and 20 CFU m-3). In the downtown area, with an urbanization index of 1.0, Penicillium spp. were more numerous than any other genus and formed 25% of the total fungal count compared with 14 and 17% in the other areas. Concentrations of airborne Penicillium spp. did not differ significantly between rainy and dry seasons.(ABSTRACT TRUNCATED AT 250 WORDS)     

Molting fluid enzymes of the tobacco hornworm,Manduca sexta: Timing of proteolytic and chitinolytic activity in relation to pre-ecdysial development

Developmental profiles for a number of molting fluid (MF) enzyme activities were established and related to the progress of pupal cuticle degradation during the four days that precede the eclosion of adult tobacco hornworms. Cuticle degrading activity, molting fluid protease 1 (MFP-1), and molting fluid protease 2 (MFP-2) all increased in activity at the time that loss of material from the old cuticle occurred. In contrast, chitinase and β-acetylglucosaminidase activities did not parallel weight loss from the old cuticle. These results are consistent with the hypothesis that proteolytic activity is a prerequisite for the action of chitinase on cuticle chitin. © 1993 Wiley-Liss, Inc.     

QUANTITATIVE BEHAVIORAL STUDY OF BOTTLENOSE DOLPHINS IN SWIM-WITH-DOLPHIN PROGRAMS IN THE UNITED STATES

The behavior of dolphins in four Swim-With-Dolphin programs was compared by type of Swim encounter, defined by the presence ("Controlled") or absence ("Not-Controlled") of explicit trainer regulation of interactions between dolphins and human swimmers. Dolphin-swimmer interactions involving aggressive, submissive, or sexual behavior were designated as "high-risk" in the Swim context; sexual behavior was included as high-risk based on analyses that demonstrated co-occurrence of sexual and agonistic behaviors. High-risk activity comprised a substantial proportion of dolphin-swimmer social activity during Not-Controlled Swims. In contrast, high-risk activity rarely occurred during Controlled Swims, even though agonistic and sexual behaviors were normal components of the same dolphins' free-time social repertoire. These results indicated that direct trainer control of dolphin-swimmer interactions virtually eliminated high-risk activity from the Swim context, and thereby diminished the potential for dolphin distress, swimmer injury, and rejection of dolphins from Swim programs due to swimmer injury. This study illustrates effective use of quantitative behavioral sampling techniques for evaluation of captive management concerns and promotes broader use of these techniques for a better understanding of cetacean behavior.     

Transport of the large-neutral amino acids by the gamma-glutamyl cycle: a proposal.

The γ-glutamyl cycle has been proposed by Meister (1973) as one possible mechanism for the mediation of amino acid transport. The high energy requirement of the pathway, the very low specificity of γ-glutamyl transpeptidase and the inability to account for trans membrane stimulation of amino acid entry are but three criticisms of this hypothesis. It is proposed that the various objections can be overcome by postulating that the soluble form of γ-glutamyl transpeptidase transfers the γ-glutamyl moiety from gluthathione to glutamine (in the case of brain) and that the membrane sequestered form of this enzyme catalyzes the exchange of the γ-glutamyl group between γ-glutamyl glutamine and an entering neutral amino acid. The released glutamine leaves the cell. The γ-glutamyl amino acid then passes into the cytoplasm where it is acted upon by either γ-glutamyl cyclotransferase or the soluble γ-glutamyl transpeptidase which transfers the γ-glutamyl group to another molecule of glutamine. It is postulated that access to the membrane-bound enzyme is dependent on the relative lipophilia of the entering large-neutral amino acids. The available data support this mechanism. By regeneration of γ-glutamyl glutamine, a low expenditure of energy is required for the transport process. Specificity of transpeptidation is attained by the constraints of access to the membrane bound enzyme site.