The interaction of testosterone and gonadotropins in stimulating estradiol and progesterone secretion by cultures of corpus luteum cells isolated from pigs in early and midluteal phase.

The first objective of this research was to define the capacity of corpora lutea of pig to secrete estradiol in the presence of an androgen substrate which was testosterone. The second objective was to define the synergism between gonadotropic hormones such as LH, FSH, and PRL and testosterone as measured by estradiol and progesterone secretion by two types of porcine luteal cells. Luteal cells were collected from newly forming corpora lutea (0-3 days after ovulation) and from mature corpora lutea (8-10 days after ovulation). After dispersion, luteal cells were suspended in medium M199 supplemented with 10% of calf serum and grown as monolayers at 37 degrees C. Control cultures were grown in medium alone while other cultures were supplemented with either testosterone alone at a concentration of 1 x 10(-7) M or with 10, 100, 500 ng LH plus testosterone, 10, 100, 500 ng FSH plus testosterone or 10, 100, 500 ng PRL plus testosterone. After 2 days of cultivation all cultures were terminated and media were frozen at 20 degrees C for further steroid analysis. Testosterone added to the culture medium in the absence of gonadotropins was without effect on estradiol and progesterone secretion by luteal cells collected in the corpora lutea of the early luteal phase. On the other hand testosterone added to the medium significantly increased progesterone and estradiol secretion by cultured luteal cells collected in the midluteal phase of the cycle. No additive stimulatory action of gonadotropins and testosterone on progesterone secretion was observed in cultures of luteal cells from the early luteal phase but this was not the case in cultures of luteal cells from the midluteal phase.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of Growth Regulators on Polyamine Content and Peroxidase Activity in Hevea brasiliensis Callus

3, 4-dichlorophenoxyacetic acid (3,4-D) and benzylaminopurine(BAP) at 9 µM (control medium) was compared with 4.5,2.25, and 0.45 µM for ability to induce callogenesis andembryogenesis from seed explants of Hevea brasiliensis. Supplyingthese growth regulators at 4.5 µM for 20 d improved embryogenicpotential compared with the control medium (El Hadrami, Carronand d'Auzac, 1991, Annals of Botany 67, 511–515), sustainedputrescine, spermidine and spermine at a higher level throughoutof much of the culture period (40–70 d), and maintainedlow levels of peroxidase activity. In the control medium, poorcallus embryogenesis is considered a consequence of rapid ageingof tissues characterized by (i) acceleration of an early buttransient production of polyamines, which promoted embryogeniccapacity, and (ii) an early peak in peroxidase activity thatwas positively correlated with callus browning, one of the factorslimiting embryogenesis. Somatic embryogenesis, polyamines, peroxidase, Hevea brasiliensis, rubber-tree     

Effect of Photoperiod and Electrical Potentials Applied to Petioles on the Glucose-6-phosphate Dehydrogenase Activity used as Marker of Floral Induction in Shoot Apices of Spinach I

The increase of glucose-6-phosphate dehydrogenase (G-6-PD) activityhas been proposed as an early marker of floral evocation inthe shoot apical meristem of spinach. This induction is obtainedby the transfer of vegetative plants from short days to continuouslight. The exposure of a single leaf to continuous light inducedthe same effect as that produced with the whole plant. In vegetativeconditions (short days), an electrical potential of ten volts(electrical current: 12·5 µA) applied to the petioleof a single leaf induced a weak increase of G-6-PD activityin the shoot apex, while under inductive conditions, this increasewas similar to that of control plants (transferred to continuouslight). Application of an electrical potential to the petioleand the root inhibits the increase linked to the inductive transfer.These results show that an externally applied electrical potentialmay interact with the natural electrical gradients along theshoot and consequently inhibit the normal floral developmentby an as yet unspecified mechanism. Spinacia oleracea, floral induction, interorganic relations, glucose-6-phosphate dehydrogenase, shoot apex, electrical potentials     

Chloroplast DNA phylogeography of the argan tree of Morocco

Polymorphisms in the chloroplast genome of the argan tree (Sapotaceae), an endemic species of south-western Morocco, have been detected by restriction site studies of PCR-amplified fragments. A total of 12 chloroplast DNA (cpDNA) and two mitochondrial DNA (mtDNA) fragments were amplified and digested with a single restriction enzyme ( Hin fI). Polymorphisms were identified in six of the cpDNA fragments, whereas no mtDNA polymorphisms were detected in a survey of 95 individuals from 19 populations encompassing most of the natural range of the species. The cpDNA polymorphisms allowed the identification of 11 haplotypes. Two lineages, one in the south-east and the other in the north-west, divide the range of the argan tree into two distinct areas. The level of genetic differentiation measured at the haplotype level ( G _STc= 0.60) (i.e. with unordered haplotypes) was smaller than when phylogenetic relationships were taken into account ( N _STc= 0.71–0.74) (ordered haplotypes), indicating that population history must be considered in the study of the geographical distribution of cpDNA lineages in this species. If contrasted with the level of nuclear genetic differentiation measured in a previous study with isozymes ( G _STn= 0.25), the results indicate a relatively high level of gene flow by seeds, or conversely a relatively low level of gene flow by pollen, as compared with other tree species. Goats and camels could have played an important role in disseminating the fruits of this tree.     

Physiological Responses of Spring Durum Wheat Cultivars to Early-season Drought in a Mediterranean Environment

The Mediterranean climate of North Africa is characterized byuncertain rainfall immediately after seedling emergence, leadingto drought early in the growing season which depresses durumwheat production. However, there is limited understanding ofthe physiological basis of resistance of spring durum wheatto drought in rainfed Mediterranean regions. The objectivesof this study were to examine differences in some physiologicalcharacters among spring durum wheat cultivars in response toduration of early-season drought, and to determine the relationshipof these characters to drought resistance. In two field experiments(1995 and 1996 growing seasons) and a glasshouse experiment(1996), six spring sown durum wheat cultivars were evaluatedunder four water regimes: well irrigated and three differentwater deficits from emergence until the onset of tillering,mid-tillering or at the end of tillering. Cultivars differedin their response. Decreases in photosynthesis soon after droughtstress was imposed resulted mainly from reduced stomatal conductance.Continued water deficits also reduced mesophyll photosyntheticactivity. Possible factors determining the drought-resistanceof a cultivar are lower sensitivity of CO₂exchange rate, netCO₂uptake to water loss ratio, stomatal resistance, relativewater content and greater osmotic adjustment under stress. Furthermore,there is sufficient intraspecific variation in these physiologicalattributes to suggest their use as selection tools.Copyright1998 Annals of Botany Company Wheat;Triticum durumDesf.; early-season drought; physiological responses.     

Thyrotropin stimulates progesterone secretion by luteal cells by activation of the cAMP/protein kinase A signaling system: a potential involvement of protein kinase C

Although the corpus luteum (CL) is not known as a target tissue for thyrotropin (TSH), this hormone increases progesterone production by porcine luteal cells cultured in vitro. In this study we investigated the optimal conditions for TSH-stimulated progesterone secretion as well as the involvement of protein kinase A (PKA) and protein kinase C (PKC) in the mechanism of TSH action on porcine luteal cells. To study the PKA and PKC signaling mechanisms, luteal cells collected from mature CL were incubated with the inhibitor of PKA and potent activators of both kinases: PKA-forskolin and PKC-phorbol ester 12-myriistate-13-acetate (PMA). The PKA inhibitor totally suppressed progesterone production in TSH alone, forskolin alone and in TSH plus forskolin-stimulated luteal cells. Forskolin increased basal (P < 0.05) and TSH-stimulated (P < 0.05) progesterone secretion and cAMP accumulation (P < 0.05). Forskolin and PMA added together to control (non-TSH-treated) luteal cells had an additive effect on progesterone production. In TSH-treated cells, the effect of PMA was statistically significant but did not show an additive effect with forskolin. Further PMA did not affect cAMP accumulation in control and TSH-treated luteal cells. Treatment of control and TSH-treated luteal cells with forskolin and PMA together showed the same increase in cAMP accumulation as with forskolin alone. This is the first demonstration that TSH acts on luteal cell steroidogenesis by activation of the cAMP/PKA second messenger system and also that the PKC signaling pathway may be involved in luteal TSH action on the corpus luteum.