Evidence for the nitrate assimilation-dependent nitrite excretion in cyanobacterium Nostoc MAC

Nitrate uptake and nitrite efflux patterns in Nostoc MAC showed a rapid phase followed by their saturation. Nitrite efflux was maximum in nitrate medium whereas the cells incubated in N₂ and NH ₄ ⁺ media exhibited a decreased nitrite efflux activity. The simultaneous presence of NH ₄ ⁺ and nitrate significantly decreased nitrite efflux. L-Methionine-Dl-sulphoximine (MSX) prevented inhibition of nitrite efflux by NH ₄ ⁺ . In the dark there was negligible nitrite efflux, whereas illumination increased the rate of nitrite efflux significantly. The nitrite efflux system was maximally operative at pH 8.0, 30°C and a photon fluence rate of 50 mol m^-2. s^-1. These results confirm that (i) the nitrite efflux system in Nostoc MAC is dependent upon nitrate uptake and assimilation and is repressible by NH ₄ ⁺ ; (ii) NH ₄ ⁺ itself is not the actual repressor of nitrite efflux; a product of NH ₄ ⁺ assimilation via glutamine synthetase (GS) is required for repression to occur; (iii) the catalytic function of GS does not appear to be involved in nitrate assimilation-dependent nitrite efflux, and (iv) the optimum pH, temperature and illumination for maximum nitrite efflux were found to be 8.0, 30°C and 50mol m^-2. s respectively.B.B. Singh, P.K. Pandey and P.S. Bisen are with the Department of Microbiology, Barkatullah University. Bhopal 462026, India. S.Singh is with the Department of Microbiology, School of Life Sciences, North Maharashtra University, Jalgaon, India     

Down-regulation of statin,a nonproliferation-specific nuclear protein,and up-regulation of c-myc after initiation of programmed cell death in mouse fibroblasts

Deprivation of growth factors has been shown to induce programmed cell death in many cell types, including mouse 3T3 fibroblasts. Programmed cell death (apoptosis) is an active process of self-destruction which is thought to require the expression of unique genes. Recently, the expression of cell cycle genes such as c-fos and c-myc, and re-entrance to cell cycle traverse, are thought to be necessary to induce programmed cell death. Previous work in this laboratory has shown that statin is a nonproliferation-specific nuclear protein present in the nuclei of young quiescent or senescent human fibroblasts, as well as in growth-arrested mouse 3T3 fibroblasts; we have reported that statin disappears rapidly after the blockage of growth arrest is removed and cells are allowed to resume cell cycle traverse. In this report we address the question of whether cells induced to enter the programmed cell death process also lose the expression of statin. We studied density-arrested quiescent mouse 3T3 cells, which undergo rapid cell death by apoptosis upon serum deprivation. Our results suggest that c-myc expression is induced, as previously reported in other systems of apoptotic death. Interestingly, we also find that statin indeed disappears after the induction of programmed cell death is initiated. These results further support the notion that when apoptosis is induced, cells behave as though released from replication arrest, and experience some part of the G₁ phase of the cell cycle. The difference between this event and normal cell cycle traverse is that this experience of the G₁ phase in the apoptotic process is an abortive one, with the end result of cell demise. © 1995 Wiley-Liss, Inc.     

Nutrient status,algal and cyanobacterial flora of six fresh water streams of Schirmacher Oasis,Antarctica

The algal and cyanobacterial flora and the chemical environment of six freshwater streams of Schirmacher Oasis, Antarctica were investigated. Over 30 species of algae, predominantly cyanobacteria (Cyanophyceae), were recorded. N₂-fixing species, both heterocystous and unicellular diazotrophs, contributed more than 50% to the counts and their dominance was greatest in the middle of the stream where nitrogen and other nutrients were low. Green algae and diatoms also contributed to the flora. The species composition varied between streams. Glacial and snow drift meltwater streams contained a distinctive community. Based on diversity indices, these streams could be classified into two clusters.     

Augmented sympathetic tone alters muscle metabolism with exercise: lack of evidence for functional sympatholysis

Shoemaker, J. Kevin, Prasant Pandey, Michael D. Herr, DavidH. Silber, Qing X. Yang, Michael B. Smith, Kristen Gray, and LawrenceI. Sinoway. Augmented sympathetic tone alters muscle metabolismwith exercise: lack of evidence for functional sympatholysis. J. Appl. Physiol. 82(6):1932-1938, 1997.It is unclear whether sympathetic tone opposesdilator influences in exercising skeletal muscle. We examined highlevels of sympathetic tone, evoked by lower body negative pressure(LBNP, 60 mmHg) on intramuscular pH and phosphocreatine (PCr)levels (³¹P-nuclear magnetic resonance spectroscopy) duringgraded rhythmic handgrip (30 contractions/min; ~17, 34, 52 and 69%maximal voluntary contraction). Exercise was performedwith LBNP and without LBNP (Control). At the end of exercise, LBNPcaused lower levels of muscle pH (6.59 ± 0.09) comparedwith Control (6.78 ± 0.05; P < 0.05). PCr recovery, an index of mitochondrial respiration, was lessduring the recovery phase of the LBNP trial. Exercise mean arterialpressure was not altered by LBNP. The protocols were repeated withmeasurements of forearm blood flow velocity and deep venous samples(active forearm) of hemoglobin (Hb) saturation, pH, and lactate. WithLBNP, mean blood velocity was reduced at rest, during exercise, andduring recovery compared with Control (P < 0.05). Also, venous Hbsaturation and pH levels during exercise and recovery were lower withLBNP and lactate was higher compared with Control(P < 0.05). We concludethat LBNP enhanced sympathetic tone and reduced oxygen transport. Athigh workloads, there was a greater reliance on nonoxidativemetabolism. In other words, sympatholysis did not occur.

     

Evidence for intracellular formation of angiotensins: coexistence of renin and angiotensin-converting enzyme in Leydig cells of rat testis

Leydig cells were purified from rat testes by discontinuous metrizamide density gradient and were shown to contain renin (EC 3.4.99.1), angiotensin-converting enzyme (dipeptidyl carboxypeptidase, (EC 3.4.15.1), and the peptide hormone angiotensins I, II and III as determined by the combined HPLC and radioimmunoassay. In germinal cells only angiotensin II (AII) was found at a significant level. These findings provide evidence for intracellular formation of AII in testicular cells and demonstrate that an intracellular renin-angiotensin system exists in normal non-transformed cells.     

Isolation of sodium chloride-tolerant callus line of Cicer arietinum L. cv. BG-203

A NaCl-tolerant callus line of Cicer arietinum has been isolated, as a spontaneous variant, on agar-solidified MS-medium supplemented with 100 mM NaCl. The growth of this line, in the presence of 100 mM NaCl, was comparable to that of the NaCl-sensitive callus line growing in the absence of NaCl. Regarding relative tolerance of the two callus lines towards NaCl (0 to 200 mM), the tolerant line performed poorly in the absence of NaCl and exhibited optimal growth at 50 mM NaCl. The tolerance persisted even after three passages of 4-wk each, tested so far, away from the selective agent.     

Evolution of incompatibility systems in plants: Complementarity and the mating locus in flowering plants and fungi

Summary The restriction of sexual pairing by a specificity gene is considered to be an ancient development in the plant kingdom. The diversity and general parallelism of incompatibility systems seen amongst the phyla at the present time can be rationalized in terms of the association of various derived forms of the ancestral specificity unit with differing spectra of accessory factors controlling sexual physiology in the different phyla. Sexual morphogenesis has become divided into distinct phases under the control of complementary genes. These phases are initiated by a regulatory system of Co-ordinator genes which control the order in which groups of morphogenetic genes are expressed during development. The entire sexual cycle will be completed only if all the complementary groups are activated in the appropriate sequence. The present article discusses essential features of the evolution of the breeding locus in different phyla. These features are consistent in themselves with the present data and are not dependent on the proposed ancient origin of the specificity gene.The above hypothesis throws light on the (1) evolution of the complex mating loci in flowering plants and fungi; (2) evolution of complementary incompatibility and heteromorphic incompatibility in flowering plants; (3) anomalous cross-compatibility behaviour of mutants in the fungus Schizophyllum commune; (4) nature of homothallism in higher fungi; (5) mode of origin of new functional self-incompatibility alleles; and (6) homogenic and heterogenic incompatibility.     

Antiulcerogenic and anti-inflammatory effects of emodin, isolated from Rhamnus triquerta wall

Emodin, an anthraquinone derivative, isolated from the whole plant of R. triquerta, in 15 mg/kg dose (ip) exhibited anti-inflammatory activity against carrageenin-induced pedal inflammation in rats. In the same dosage it also showed antiulcer activity against 4 hr pylorus-ligated, aspirin and immobilization stress-induced gastric ulcers in rats. It decreased acid and pepsin output and augmented mucus secretion in terms of total carbohydrate: protein ratio in the gastric juice of aspirin treated pylorus-ligated rats, indicating that the antiulcerogenic effect of emodin may be due to its effect on gastric secretion.     

Structure and seasonal dynamics of humid tropical grasslands in Meghalaya,India

Abstract. Four humid grassland communities at three different locations in Meghalaya, India were analysed during 1988 and 1989 for species and life-form composition, diversity and dominance in relation to altitude, soil and prevailing disturbances. Due to the adverse interactive influences of exceptionally high annual rainfall (> 10 000 mm), topography and human interference on soil fertility, the grassland at Cherrapunji, at 1300 m altitude, had a low species diversity (H'= 1.74) and was dominated by three perennial grass species. Similar grasslands, at both higher and lower altitudes on fertile soil and with lower rainfall (ca. 2000 mm), showed higher diversity values (H'= 2.28 at Burnihat and 2.31 at Upper Shillong). The proportion of perennial species and chamaephytes increased with elevation. At the high altitude site a grassland under short-term protection from fires and grazing had a higher species richness, density and basal cover than an unprotected grassland. All grasslands show a clear seasonality, albeit with different patterns, with a maximum in density and basal cover in August. The differences in structure and seasonality are discussed in terms of different levels of stress.