Morphogenesis of mechanoreceptor and epidermal cells of crickets during the last instar,and its relation to molting-hormone level

Summary (1) The fine structure of the cercal campaniform sensilla and epidermal cells of Gryllus bimaculatus Deg. (Saltatoria, Gryllidae) was examined, and the ecdysteroid level was monitored throughout the last larval instar. (2) The epidermal cells show changes in shape, cytoplasmic inclusions and differentiation of the apical cell membrane, coupled to the phases of buildup and breakdown of the (cercus) cuticle. (3) The imaginal epicuticle of the epidermal cells begins to form later (by about approximately 6 h) than that of the campaniform sensilla. (4) The campaniform sensilla were studied with respect to (a) the morphogenesis of the cuticular apparatus, (b) the inclusion of phenol oxidases in the cuticular apparatus, and (c) changes in the sensory apparatus preparatory to molting. (5) After apolysis the folding of the tormogen-cell wall into microvilli transiently disappears. Microvilli re-form shortly before imaginai ecdysis, and at the same time an outer receptor-lymph space develops. The role of the tormogen-cell plaques is discussed. (6) The levels of - and -ecdysone were determined separately by radioimmunoassay. (7) At the beginning of the instar the hormone level, especially that of -ecdysone, falls. Prior to apolysis, the concentration of -ecdysone rises, reaching an intermediate peak after apolysis is complete. The maximum hormone concentration (approximately 2,000 ng/g) is reached after the cuticulin layer is deposited, primarily due to the increase in -ecdysone. While the proecdysial cuticle is forming, the hormone titer is reduced; at this time -ecdysone is its chief component. (8) The identification of the ecdysteroids monitored by radioimmunoassay was confirmed by gas chromatography.This paper is dedicated to Professor H. Risler on the occasion of his 65th birthdaySupported by the Deutsche Forschungsgemeinschaft     

Stereoselective synthesis of (22R)- and (22S)-castasterone/ponasterone A hybrid compounds and evaluation of their molting hormone activity

Two stereoisomers of a castasterone/ponasterone A hybrid compound, the (20R,22R) and (20R,22S)-isomers of 2alpha,3alpha,20,22-tetrahydroxy-5alpha-cholestan-6-one, were synthesized stereoselectively and their binding activity to the ecdysteroid receptor was determined. From the concentration-response curve for the inhibition of the incorporation of tritiated ponasterone A into ecdysteroid receptor containing insect cells, the concentration (IC50) required to inhibit 50% of the incorporation of radioactivity into cells was evaluated. The IC50 values of the (22R)- and (22S)-isomers were determined to be 0.30 and 38.9 microM against Kc cells, respectively, indicating that the (22R)-isomer is about 100 times more potent than the corresponding (22S)-isomer. IC50 values of these compounds against lepidopteran Sf-9 cells were determined to be 0.36 and 12.9 microM, respectively. The molting hormonal effect was examined in a Chilo suppressalis integument system and the 50% effective concentration for the stimulation of N-acetylglucosamine incorporation into the cultured integument was determined to be 2.7 microM for the (22R)-isomer, while the (22S)-isomer was inactive. On the other hand, both isomers did not show brassinolide-like activity in the rice lamina inclination assay.     

Regulation of translation elongation and phosphorylation of eEF2 in rat pancreatic acini

While pancreatic protein synthesis and the initiation of translation are regulated by hormones and neurotransmiters, whether the elongation process is also regulated is unknown. Stimulatory doses of cholecystokinin (CCK) (100 pM), bombesin (10 nM), and carbachol (10 microM) increased elongation rates (measured as ribosomal half-transit time) in pancreatic acini in vitro. At the same time these secretagogues reduced elongation factor 2 (eEF2) phosphorylation, the main factor known to regulate elongation, and increased the phosphorylation of the eEF2 kinase. The mTOR inhibitor rapamycin reversed the dephosphorylation of eEF2 induced by CCK, as did treatment with the p38 MAPK inhibitor SB202190, the MEK inhibitor PD98059, and the phosphatase inhibitor calyculin A. Neither rapamycin, SB202190, PD98059 nor calyculin A had an effect on CCK mediated eEF2 kinase phosphorylation. Translation elongation in pancreatic acinar cells is likely regulated by eEF2 through the mTOR, p38, and MEK pathways, and modulated through PP2A.     

Antioxidant Enzyme Isoforms on Gels in Two Poplar Clones Differing in Sensitivity After Exposure to Ozone

The effect of acute ozone (O₃) fumigation on isozyme patterns of superoxide dismutase (SOD), peroxidase (POD) and ascorbate peroxidase (APX) in mature (ML) and young leaves (YL) of two poplar clones, contrasting in O₃-sensitivity was analysed. Untreated leaves of both the O₃-sensitive (O₃-S) clone Eridano of Populus deltoides×P. maximowiczii and the O₃-resistant (O₃-R) clone I-214 of P.×euramericana showed four distinct SOD isoforms with a relative mobility (R_f) of 0.54 (MnSOD), 0.60 (Cu/ZnSOD), 0.65 (unidentified), and 0.71 (Cu/ZnSOD). After O₃-fumigation the activity of the SOD isoforms showed only quantitative variations with respect to control plants. In ML of untreated O₃-R plants seven POD isoforms (R_f= 0.13, 0.19, 0.34, 0.59, 0.64, 0.70 and 0.75) were found, while in YL one isoform (R_f= 0.34) was undetected. Only three POD isoforms in both ML and YL of untreated O₃-S plants were resolved. The electrophoretic pattern of POD in O₃-S leaves was greatly modified by acute O₃-fumigation with the appearance of new isoforms in both YL and ML and the disappearance of an isoform (R_f= 0.13) in YL. Additionally, O₃-exposure induced the appearance of two APX isoforms in YL (R_f= 0.66 and 0.70), and one isoform in ML (R_f= 0.70) of the O₃-S clone. By contrast, the activity of the three APX isoformes (R_f= 0.64, 0.70 and 0.76) detected in O₃-R leaves showed only quantitative variation with respect to untreated plants. From these data it is concluded that: 1) in these poplar hybrids antioxidant enzyme activity is developmentally regulated and greatly affected by acute O₃ stress treatments and 2) the different enzymes activity displayed by the two poplar clones, especially for POD and APX isoformes, could partly explain their distinct O₃-sensitivity.     

Effects of inhibitors of polyamine biosynthesis and of polyamines on strawberry microcutting growth and development

The primary free polyamines identified during growth and development of strawberry (Fragaria × ananassa Duch.) microcuttings cultivated in vitro were putrescine, spermidine and spermine. Polyamine composition differed according to tissue and stages of development; putrescine was predominant in aerial green tissues and roots. -DL-difluoromethylarginine (DFMA), a specific and irreversible inhibitor of the putrescine-synthesizing enzyme, arginine decarboxylase (ADC), strongly inhibited growth and development. Application of agmatine or putrescine to the inhibited system resulted in a reversal of inhibition, indicating that polyamines are involved in regulating the growth and development of strawberry microcuttings. -DL-difluoromethylornithine (DFMO), a specific and irreversible inhibitor of putrescine biosynthesis by ornithine decarboxylase, promoted growth and development. We propose that ADC regulates putrescine biosynthesis during microcutting development. The application of exogenous polyamines (agmatine, putrescine, spermidine) stimulated development and growth of microcuttings, suggesting that the endogenous concentrations of these polyamines can be growth limiting.Abbreviations ADC arginine decarboxylase - ODC ornithine decarboxylase - DFMA -difluoromethylarginine - DFMO -difluoromethylornithine - Put putrescine - Spd spermidine - Sp spermine - DW dry weight - PA polyamine - PPF photosynthetic photon flux     

Estimating estuarine residence times in the Westerschelde (The Netherlands) using a box model with fixed dispersion coefficients

The residence time of the water masses in the Westerschelde estuary was determined using a simple compartment-model that simulates the advective-diffusive transport of a conservative dissolved substance (chlorinity). The residence time of a water parcel in the upstream part of the estuary (i.e. the time needed for this water parcel to leave the estuary) varied from about 50 days in winter to about 70 days in summer. The most seaward compartment had residence times of about 10-15 days.Dispersive coefficients that are fixed in time were able to reproduce the observed salinity distributions very well in the Westerschelde. They were obtained by calibration on observed chlorinities. It is argued that the apparent relationship of dispersive coefficients with freshwater flow, which is observed in certain studies, could (partly) reflect the deviation from steady state conditions which are required assumptions to calculate these dispersive coefficients directly from salinity profiles.     

Increased taxane accumulation in callus cultures of Taxus cuspidata and Taxus × media by some elicitors and precursors

In Taxus cuspidata callus, vanadyl sulfate (10 mg l^–1) induced a high (146 g g^–1 dry wt) production of 10-deacetylbaccatin III in comparison to 7 g g^–1 dry wt of the control. The content of paclitaxel in this species increased from 16 g g^–1 to 74 g g^–1 dry wt when 20 mg phenylalanine l^–1 was used. In T. media, p-aminobenzoic acid induced the highest content of 10-deacetylbaccatin III (481 g g^–1 dry wt) versus 181 g g^–1 in the control. Paclitaxel increased from 89 to 139 g g^–1 dry wt after adding chitosan (20 mg l^–1) to the cultures.     

Identification of gibberellins in leaf exudates of strawberry (Fragaria ×ananassaDuch.)

Leaf exudates from the short-day (SD) strawberry (Fragaria × ananassa Duch.) cv. Elsanta were analysedfor gibberellin (GA) content using combined gaschromatography – mass spectrometry (GC-MS). Comparison of full-scan mass spectra and Kovatsretention indices (KRIs) with those of standardsrevealed the presence of GA₁, GA₃, 3-epiGA₁ and GA₃-isolactone.