Differential Effects of Nitrate and Light on the Expression of Glutamine Synthetases and Ferredoxin-Dependent Glutamate Synthase in Maize

The effects of nitrate and light on the expression of genesfor glutamine synthetase (GS) isoproteins and ferredoxin-dependentglutamate synthase (Fd-GOGAT) were studied in different organsof maize seedlings by analyzing the levels of the respectivepolypeptides and mRNAs. In roots, the levels of plastidic GSand of a novel, root-specific GS molecule localized in the extraplastidiccompartment were increased markedly by nitrate, whereas Fd-GOGATand cytosolic GS remained at their initial levels. Ammonia wasnot effective in inducing the plastidic GS and Fd-GOGAT butit did induce the novel GS isoprotein. In leaves, cytosolicand plastidic GSs and Fd-GOGAT were present in both mesophyllcells (MC) and bundle sheath cells (BSC). Upon addition of nitrate,the level of plastidic GS increased preferentially in MC, andupon exposure of etiolated seedlings to light, the levels ofplastidic GS and Fd-GOGAT increased in BSC in a coordinatedmanner. The relationship between the expression of genes forGSs and Fd-GOGAT and the physiological role of the GS/GOGATcycle is discussed in terms of the characteristics of nitrogenmetabolism in roots, MC, and BSC. (Received August 11, 1992; Accepted September 21, 1992)     

cDNA Cloning of Indole-3-Acetic Acid-Regulated Genes: Aux22 and SAUR from Mung Bean (Vigna radiata) Hypocotyl Tissue

Five cDNAs of auxin-regulated genes were isolated from mungbean (Vigna radiata) hypocotyl sections by differential hybridizationscreening. They were related to the soybean genes, Aux22 [Ainleyet al. (1988) J. Biol. Chem. 263: 10658] and SAUR [McClure etal. (1989) Plant Cell 1: 229]. Regulation of expression of thesegenes, examined by Northern blot analysis, appeared similarto that reported in soybean hypocotyls. (Received August 10, 1991; Accepted October 14, 1991)     

Comparison of osteoporosis and calcium intake between Japan and the United States.

The number of osteoporotic females in Japan with vertebral bone mineral density measured by dual energy x-ray absorptiometry, defined as less than -3 SD of the peak bone mass, is approximately 10,000,000, corresponding to 8% of the whole population of Japan. While this value approximately corresponds to the prevalence of low bone mineral density in the United States, the incidence of hip fracture appears to be much less in Japan than in the United States, 50,000 per 125,000,000 per year compared with 250,000 for a population twice as large. This seems to be paradoxical because of the lower bone mineral density and lower calcium intake in Japan, with 400-500 mg/day mainly as soybean products, small fish with bones, and vegetables. The difference in hip fracture incidence, however, may not actually be as wide as it seems when the larger number of bedridden elderly subjects in Japan is taken into consideration. In these bedridden subjects with severe immobilization osteoporosis, hip fracture is only prevented by the fact that they are not ambulatory. Life-style difference may also offer an explanation. Sitting on a tatami mattress on completely flexed knees with frequent standing up, along with other household work, in a narrow home space may ensure a marked development of hip musculature and also provide skill in balancing oneself to prevent fails. The difference in fracture incidence should be analyzed from various angles to obtain a firm ground for the future prevention of hip fracture due to osteoporosis. Although osteoporosis universally affects all races and nationalities, conspicuous differences may be encountered in the severity of its manifestations and complications.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of elevated extracellular calcium on the proliferation of osteoblastic MC3T3-E1 cells:its direct and indirect effects via monocytes.

There has been evidence that elevated calcium concentration at the resorptive site of the bone directly regulates osteoclast function. In the present study, in order to clarify the role of elevated calcium concentration at the resorptive site in the regulation of osteoblast function, not only direct but also indirect effect via human monocytes of the increase in extracellular calcium (Cae) on the proliferation of osteoblastic MC3T3-E1 cells have been investigated in serum-free condition. The increase in Cae enormously stimulated osteoblast proliferation at the concentration of 3 to 20 mM. When human monocytes were cultured at the elevated Cae concentration, monocyte-conditioned medium-induced stimulation of osteoblast proliferation was significantly amplified. Present data demonstrate that elevated Cae has pronounced stimulatory effect on osteoblast proliferation not only directly but also indirectly via monocytes. Calcium released from bone matrix at the resorptive sites might be linked to the coupling of osteoclast and osteoblast functions.     

The activation of cAMP-dependent protein kinase is directly linked to the inhibition of osteoblast proliferation (UMR-106) by parathyroid hormone-related protein

The present study was performed to compare the effect of parathyroid hormone-related protein (PTHrP) on the proliferation of osteoblastic osteosarcoma cells (UMR-106) with that of PTH and characterize the direct involvement of cAMP in the change of osteoblast proliferation by PTHrP. Human(h)PTHrP-(1-34) (10(-11)-10(-7)M) dose-dependently inhibited [3H]thymidine incorporation (TdR) in the same manner as hPTH-(1-34). The simultaneous addition of PTHrP and PTH at a maximal effective dose of 10(-7) M did not cause additive suppressive effect on cell proliferation. Rp-cAMPs, which has been recently shown to act directly as antagonist in the activation of cAMP-dependent protein kinase (PKA), dose-dependently (10(-6)-10(-4)M) antagonized PTHrP-induced suppression of TdR in the same manner as PTH. Present study indicated that PTHrP has the same effect on osteoblast proliferation as PTH and that the activation of PKA is directly linked to the change of osteoblast proliferation by PTHrP.     

Direct inhibitory effect of amino-terminal parathyroid hormone fragment [PTH(1-34)] on PTH secretion from bovine parathyroid primary cultured cells in vitro

We have examined the possibility of direct inhibitory effect of PTH(1-34) on PTH secretion in bovine parathyroid cells. As low as 10(-12) M PTH(1-34) completely inhibited low calcium (0.5 mM Ca2+)-stimulated PTH secretion by these cells. In the presence of 1.25 mM Ca2+, 10(-12) M PTH(1-34) inhibited PTH secretion by about 14.3% of the basal value, while 10(-11) M or higher concentration of PTH(1-34) showed potent inhibitory effects equivalent to the inhibitory action of high calcium concentration (2.5 mM Ca2+) on PTH secretion. At 2.5 mM Ca2+, as much as 10(-9) M PTH(1-34) failed to inhibit PTH secretion further. These results suggest that PTH(1-34) might directly, not via calcium concentration, inhibit PTH secretion by parathyroid cells and that a cooperative mechanism could exist between calcium and PTH(1-34) to inhibit PTH secretion.     

The effect of 1,25-dihydroxyvitamin D3 on human osteoblast-like osteosarcoma cell: modification of response to PTH

The influence of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] on adenylate cyclase responsiveness in cultured osteoblastic cells was studied using a human osteosarcoma cell line SaOS-2. 1,25(OH)2D3 treatment had no effect on cell growth, cell protein and alkaline phosphatase activity. 1,25(OH)2D3 did not alter the basal production of cyclic AMP (cAMP) in intact cells, but the cAMP formation in response to parathyroid hormone (PTH), isoproterenol (ISO) and cholera toxin was attenuated by 1,25(OH)2D3. The response to forskolin, however, was unaffected by 1,25(OH)2D3 treatment. Islet activating protein failed to modify these 1,25(OH)2D3 effect. In cell free experiments, 1,25(OH)2D3 showed similar effect--that is, PTH and ISO-stimulated adenylate cyclase activity were attenuated, but forskolin-stimulated adenylate cyclase was unaffected. 1,25(OH)2D3 treatment had no effect on the kinetics of PTH binding to PTH receptor and on the ADP ribosylation of GTP stimulatory binding protein (Gs) in SaOS-2 cells. According to these results, 1,25(OH)2D3 appeared to change the coupling of Gs with adenylate cyclase, but does not affect receptor, Gs and adenylate cyclase themselves, nor GTP inhibitory binding protein.     

Global stability of stationary solutions to a nonlinear diffusion equation in phytoplankton dynamics

We consider a nonlinear diffusion equation proposed by Shigesada and Okubo which describes phytoplankton growth dynamics with a selfs-hading effect.We show that the following alternative holds: Either (i) the trivial stationary solution which vanishes everywhere is a unique stationary solution and is globally stable, or (ii) the trivial solution is unstable and there exists a unique positive stationary solution which is globally stable. A criterion for the existence of positive stationary solutions is stated in terms of three parameters included in the equation.