Sub-Cellular Distribution of Zinc in Different Vegetative Organs and Their Contribution to Grains Zinc Accumulation in Rice Under Different Nitrogen and Zinc Supply

Journal of Plant Growth Regulation - Zinc is an important micronutrient for the growth and development of human body and plants. Proper use of nitrogen fertilizer and foliar application of Zn have...     

Intraspecific molecular variation inHieracium sect.Alpina (Asteraceae), an apomictic group

Intraspecific variation of four agamospecies ofHieracium sect.Alpina was studied using RAPD and isozyme techniques. No variation in either multiprimer RAPD or multi-enzyme phenotypes was observed withinH. holosericeum, suggesting that this widespread species consists of only a single genotype. A low level of within-population isozyme variation was seen inH. tenuifrons andH. calenduliflorum, the origin of which appears to be consistent with somatic mutation. Most isozyme and all RAPD variation in these two species was partitioned between populations. A strong correlation with geography suggests that its cause may be due to polytopic (-polyphyletic?) origin or perhaps to mutation and dispersal. The most variable species wasH. alpinum, in which isozyme variation occurred mostly within populations rather than between them, suggesting occasional sexual events or that the parents ofH. alpinum were heterozygous. RAPD variation in this species, in contrast, was partitioned between Scottish and Swiss populations, suggesting the existence of geographical races.     

Expression of Bcl-2 protein in the epiphyseal plate cartilage and trabecular bone of growing rats

 The protooncogene protein, Bcl-2, protects cells from apoptosis and ensures their survival in vitro by inhibiting the action of the apoptosis-inducer, Bax. Its expression in proliferative and long-lived cells in vivo also indicates that it protects against cell death. The chondrocytes of the epiphyseal plate cartilage undergo a series of maturation steps and deposit mineral in the cartilage matrix before dying. The possibility that Bcl-2 helps protect chondrocytes until mineral deposition is completed was investigated by determining the distribution of Bcl-2 immunoreactivity in the epiphyseal plate cartilage of growing rats and its subcellular localization, using a specific antibody. The involvement of Bax in the triggering of chondrocyte death was checked by immunocytochemistry. Bcl-2 expression in the osteoblasts and the final result of their evolution, the osteocytes, was also examined in trabecular bone. Bcl-2 immunoreactivity was non-uniformly distributed throughout the epiphyseal cartilage. It was maximal in proliferative chondrocytes, decreased in mature chondrocytes, and low in hypertrophic chondrocytes, whereas there was Bax immunoreactivity in all chondrocytes examined. Immunolabeling was intense in osteoblasts but considerably lower in fully differentiated osteocytes. Bcl-2 immunoreactivity was mainly in the cytoplasm of chondrocytes, osteoblasts, and early osteocytes; the nuclei appeared clear. The subcellular distribution of Bcl-2 immunolabeling in chondrocytes, revealed by gold particles in the electron microscope, showed that gold particles were frequently concentrated in the mitochondria in all the cartilage zones and lay mainly within the organelles, not at their periphery. The endoplasmic reticulum contained moderate immunoreactivity and there were few gold particles in the cytoplasm and nuclei. The number of gold particles decreased in all the subcellular compartments from proliferative to hypertrophic chondrocytes. In contrast, Bax immunoreactivity changed little during chondrocyte terminal evolution, and its subcellular distribution mirrored that of Bcl-2. These immunocytochemical data indicate that Bcl-2 helps maintain chondrocytes and osteoblasts until their terminal maturation. Accepted: 19 February 1997     

Effects of forskolin and cholera toxin on cyclic AMP release in a neurotensin-secreting rat C-cell line

The effects of forskolin and cholera toxin on the regulation of cAMP release were studied in a neurotensin-secreting rat C-cell line. The interaction of these agents with norepinephrine, a potent neurotensin secretagogue, was also investigated. Forskolin stimulated cAMP release 10(2)-10(3) fold while it increased neurotensin release 2-3 fold. Cholera toxin caused a 10(2)-10(3) fold increase in cAMP release and had no effect on neurotensin release. We conclude that the 44-2 C-cells provide a new model for studying the regulation of the concomitant (via forskolin) or independent (via cholera toxin) secretion of cyclic AMP and/or neurotensin.     

Ontogeny of the response to growth hormone-releasing factor

Primary cell cultures were prepared from fetal, neonatal and adult rat pituitaries and evaluated for their ability to secrete growth hormone (GH) in response to growth hormone-releasing factor (GRF). Pituitary cells prepared from fetuses at days 19 and 21 of gestation, neonatal animals at the day of birth (day 0) or the following day (day 1) and peripubertal male rats showed full dose response curves to GRF with maximal GH release when stimulated with 1 X 10(-10) M rat GRF. At this concentration of GRF, the amount of GH released was not different from that elicited by activation of adenylate cyclase with 1 X 10(-5) M forskolin. In contradistinction, a preparation of cells from fetuses at day 18 of gestation did not show the same release of GH when challenged with 1 X 10(-10) M GRF and forskolin (0.057 +/- 0.001, compared to 0.076 +/- 0.003 micrograms/10(5) cells per 4.5 h), although the cells clearly responded to both secretagogues (basal levels of GH, 0.029 +/- 0.002 micrograms/10(5) cells per 4.5 h). While cells prepared from fetuses at day 21 of gestation or from animals after birth released 5-10% of their total cellular GH content, those prepared from 18- and 19-day fetuses released as much as 40% of their total GH suggesting there is a maturation of intracellular GH processing that occurs late in gestation. The results show that, in late pregnancy, the rat fetal pituitary is highly responsive to growth hormone-releasing factor and suggest that this peptide participates in regulating GH levels during the perinatal period.     

Transformation-defective mutants of polyomavirus middle T antigen associate with phosphatidylinositol 3-kinase (PI 3-kinase) but are unable to maintain wild-type levels of PI 3-kinase products in intact cells.

Middle T antigen (MT) of polyomavirus causes transformation by associating with a number of cellular proteins. The association with and activation of two such proteins, phosphatidylinositol 3-kinase (PI 3-kinase) and pp60c-src, appears to be necessary for transformation by MT. The tyrosine kinase activity of MT-associated pp60c-src is significantly increased when assayed in vitro, and levels of phosphotyrosine-containing proteins are elevated in vivo. Similarly, levels of the PI 3-kinase products phosphatidylinositol-3,4-bisphosphate [PI(3,4)P2] and phosphatiylinositol-3,4,5-trisphosphate [PI(3,4,5)P3] are constitutively elevated in MT-transformed cells. However, the formation of a complete MT/cellular protein complex and the activation of tyrosine kinase are not sufficient to cause transformation, since the transformation-defective mutants 248m and dl1015 associate with all wild-type MT-associated proteins, including PI 3-kinase and pp60c-src, and neither mutant appears to be defective in MT-associated tyrosine kinase activity. Studies presented here compared (i) the amount of PI 3-kinase activity associated with the MT complex and (ii) levels of [3H]inositol incorporation into PI 3-kinase products in cells expressing mutant or wild-type MT. The results show that dl1015 is defective in both assays, whereas 248m is defective only for incorporation of [3H]inositol into PI(3,4,5)P2 and PI(3,4)P3. These findings identify a biochemical defect in the 248m mutant and corroborate previous results correlating transformation and elevated levels of PI 3-kinase products in vivo. In addition, they indicate that PI 3-kinase product levels are affected by factors other than simply the amount of PI 3-kinase activity associated with the MT complex.     

Distribution and behaviour of Acetes sibogae Hansen (Decapoda, Crustacea) in an estuary in relation to tidal and diel environmental changes

Quantitative samples of Acetes sibogae were collected at 2 hintervals for 48 h at three sites across the axis of a tidalestuary to examine their distribution within the water bodyover tidal and diel cycles, and to assess the role of behaviourin maintaining population distribution in estuarine/coastalwaters in relation to selected environmental factors. Watertemperature, salinity, tidal height and light intensity wereconcurrently measured. Distribution of the shrimp across theestuary was uniform and consistent between daylight or darkperiods, and among flood or ebb tides. Changes of A.sibogaeabundance were related to light and tidal cycles at each sitewith higher catches in dark periods and during flood tides.Acetes sibogae also exhibited both nocturnal and tidal verticalmovements in the water body, with greater numbers being onlyfound near-surface rather than near-bottom during flood tidesand at night. No significant differences in the distributionof size groups were found between any sampled levels of anysite. Acetes sibogae was highly aggregated in the water body.It is suggested that aggregating behaviour and tidal and nocturnalvertical movements act to facilitate population maintenancein estuarine/coastal waters.     

Modulation of hepatic level of microsomal testosterone 7 alpha-hydroxylase, P-450a (P450IIA), by thyroid hormone and growth hormone in rat liver

The effects of thyroid hormone and growth hormone on microsomal testosterone 7 alpha-hydroxylase, P-450a, were studied to understand the interaction of these hormone-mediated regulations in rats. In Western blots using anti-P-450a IgG, 1.7-fold higher content of P-450a was observed in livers of female than male adult rats, while no appreciable sex-related difference was detected in prepubertal rats and rats of 24 months of age. Treatment with n-propyl-2-thiouracil or thyroidectomy of male rats increased by 2-fold the hepatic content of P-450a, but neither regimen had a significant effect on the content in female rats. Levels of P-450a in both sexes of thyroidectomized rats were decreased by the supplementation of triiodothyronine (T3, 50 micrograms per kg, i.p. for 7 days) to levels similar to that observed in normal male rats. Hypophysectomy also caused an increase in microsomal P-450a content in male rats. Continuous infusion of human growth hormone, which mimicked the female secretion, further significantly increased the content in hypophysectomized rats to a level similar to that observed in normal female rats. In contrast, hepatic level of P-450a in hypophysectomized male and female rats was reduced by intermittent injection, which mimicked the male secretion. Clear suppression on the level of hepatic P-450a was also observed by the treatment of hypophysectomized rats with 5 or 50 micrograms/kg of T3 and of hGH-infused hypophysectomized rat with 50 micrograms/kg of T3.(ABSTRACT TRUNCATED AT 250 WORDS)