Parenchyma: a neglected plant tissue in the <Emphasis Type="Italic">Cecropia</Emphasis>/ant mutualism

The Cecropia/Azteca association is a well studied and perhaps the best known mutualistic system in the Neotropics. In this study we assessed the ultrastructure of the parenchymal tissue of the septum inside the internodes of two Cecropia species, Cecropia obtusifolia (a myrmecophytic species) and C. angustifolia (a non-myrmecophytic species), through the use of scanning electron microscopy. We found a series of large oval cavities in the parenchyma of C. obtusifolia, which were absent in the parenchyma of C. angustifolia, and which seemed to be spatially associated with vascular bundles. We also found two layers of fibers in C. obtusifolia, one on each side of the septum. Finally, the parenchymal cells of C. angustifolia were filled with several tiny oval bodies, which appeared to be plastids (perhaps serving as storage) and which were completely absent in C. obtusifolia. The structural differences between these two Cecropia species, as well as other evidence from the behavior of the ants, suggests that the parenchyma of myrmecophytic Cecropia species provides an additional source of nutrition for the Azteca queens during colonization of Cecropia saplings. Other possible uses of parenchymal tissue by the ant colony are also discussed.     

The isolation and sequencing of human gastric inhibitory peptide (GIP)

Human GIP 1-42 and fragments of human GIP corresponding to GIP 10-42, GIP 11-42, and GIP 17-42 were isolated from acid-ethanol extracts of human small intestines with the aid of an anti-GIP serum specific for the extreme C-terminal portion of the GIP molecule. The full sequence of human GIP has been established by Edman degradation of these peptides and fragments thereof by automatic gas-phase sequencing. Human GIP differs from porcine GIP at residues 18 and 34. The sequence of human GIP is thus: (Formula: see text) Amino acid residues 18 and 34 are Arg and Ser, respectively, in porcine GIP.     

Foliole movement and canopy architecture of Larrea tridentata (DC.) Cov. in Mexican deserts

Summary The creosote bush (Larrea tridentata) is a common desert perennial with bifoliate, amphistomatic, divaricate leaves. The leaves can vertically close their folioles and vary their profile with respect to direct solar radiation. Field data from different Mexican deserts showed a significant correlation between foliole aperture and mean foliole inclination: in plants in which folioles were more open, the foliole surfaces were less vertical. In a series of field experiments in the Chihuahuan Desert, foliole aperture varied significantly with the water-status of the plant and the hour of the day. In moist plants, folioles opened in the early morning and closed in the afternoon. Water-stressed plants showed significantly lower foliole apertures. A simulation of the light interception patterns of the plants showed that foliole closure in water-stressed individuals reduces direct radiation interception by around 24%. Most (64%) of the reduction in interception was due to the vertical inclination of the photosynthetic surfaces induced by foliole closure in the water-stressed plants. The rest (36%) of the reduction in interception was due to differential self-shading between foliole pairs, which was higher in the closed folioles of the water-stressed plants, but operated more towards the early hours of the day.     

Effects of soil flooding,sunlight and herbivory on seedlings of Annona glabra and Pachira aquatica in a tropical swamp

Wetlands Ecology and Management - Wetland seedlings, in addition to dealing with the effects of flooding, must gain access to sunlight and avoid herbivore damage in order to establish....     

Resistance of succinic acid dimethyl ester insulinotropic action to exendin (9-39) amide.

Exendin (9-39) amide (Ex [9-39]) was recently proposed for use in the treatment of alimentary or reactive hypoglycaemia. It was indeed found to antagonise the insulinotropic action of GLP-1 in rats infused with the dimethyl ester of succinic acid (SAD). We have now investigated whether, under comparable experimental conditions, Ex (9-39) also opposes the insulin-releasing action of SAD itself. Since this was not the case, Ex (9-39) could be safely used to abolish the incretin effect of GLP-1 without interfering with the control of insulin secretion by circulating nutrients.     

The importance of employing homologous serum free of thyronines in radioimmunoassays to assess circulating thyroid hormones in rainbow trout.

Although abundant, available information regarding the values of circulating thyronines in the rainbow trout is misleading and confusing. The present study demonstrates the importance of maintaining species serum-homology when measuring thyronines with RIA to avoid spurious results. The utilization of homologous (trout) serum free of thyronines in the standard curve allowed the standardization of accurate and specific radioimmunoassays to quantitate circulating T3 and T4 levels in 10 microliters of rainbow trout serum. Detection limit was 50 pg for both thyronines. Inter- and intra-assay coefficients of variation were minor to 10%. Mean values for T3 and T4 +/- SEM in the trout population studied (n = 34) were 23.6 +/- 1.2 and 12.0 +/- 2.3 ng/ml respectively. A positive and significant correlation (p < 0.005) between body weight and T3 was observed, confirming the active participation of this thyronine in growth processes.