Growth and yield of maize at different altitudes in Rhodesia

A late (SR 52) and an early (N × K) variety were grown, with irrigation, on well fertilized soil at three sites, Chiredzi (altitude 420 m), Henderson (1260 m) and Grasslands (1620 m). Mean incoming radiation was similar at all sites, while mean temperature decreased as altitude increased. Final total and grain dry weights were greatest at Henderson, and those of SR 52 exceeded those of N × K, although not greatly at Chiredzi. Initially, leaf area index (L) decreased with increase in altitude, but plants flowered later as altitude increased, and L at the time of flowering was greatest at Henderson. L at flowering was greater in SR 52 than in N × K, though only slightly so at Chiredzi. Leaves withered sooner after flowering at Chiredzi and Grasslands than at Henderson, but leaves of the two varieties withered at about the same time after flowering at each site. During most of the vegetative phase the efficiency of the leaves and crop growth rate (C) increased with decrease in altitude, and were greater in N × K than in SR 52. More dry matter was accumulated after flowering at Henderson than at the other sites, and more by SR 52 than by N × K at Henderson and Grasslands, but not at Chiredzi. Leaf area duration (D) after flowering was greater at Henderson than elsewhere, and greater in SR 52 than in N × K, except at Chiredzi. After flowering leaf efficiency (dry weight increase ÷D) was least at Henderson and greatest at Grasslands, but differed little between varieties at each site. The fraction in the grain of the dry matter accumulated after flowering decreased with increase in altitude and was greater in SR 52 than in N × K.     

Genetic Association between H-2 Gene and Testosterone Metabolism in Mice

SEVERAL characters involved in sexual dimorphism or male reproductive performance are influenced by genetic factors that are linked with the histocompatibility-2 (H-2) system of the mouse. These factors influence sperm cell production and function^1–4 interstrain differences in relative weights of vesicular gland and testis^4,5, immune response to the male-specific histocompatibility antigen^6,7 and an androgen-dependent allotypic serum protein designated Slp⁸. Our finding of an H-2 linked gene influencing the size of such male hormone-dependent organs, as is the vesicular gland and testis, suggested that the amount of testosterone in plasma may be influenced by an H-2 linked gene. Whereas the genetic control of some hormonally determined traits is considered to be polygenic^9,10, other data indicate some endocrine variation is due to allelic substitution at a single locus or very few loci^11–14. These genes in the mouse genome have not yet been located.     

Nitrite reductase activity of hemoglobin as a systemic nitric oxide generator mechanism to detoxify plasma hemoglobin produced during hemolysis

Hemoglobin (Hb) potently inactivates the nitric oxide (NO) radical via a dioxygenation reaction forming nitrate (NO(3)(-)). This inactivation produces endothelial dysfunction during hemolytic conditions and may contribute to the vascular complications of Hb-based blood substitutes. Hb also functions as a nitrite (NO(2)(-)) reductase, converting nitrite into NO as it deoxygenates. We hypothesized that during intravascular hemolysis, nitrite infusions would limit the vasoconstrictive properties of plasma Hb. In a canine model of low- and high-intensity hypotonic intravascular hemolysis, we characterized hemodynamic responses to nitrite infusions. Hemolysis increased systemic and pulmonary arterial pressures and systemic vascular resistance. Hemolysis also inhibited NO-dependent pulmonary and systemic vasodilation by the NO donor sodium nitroprusside. Compared with nitroprusside, nitrite demonstrated unique effects by not only inhibiting hemolysis-associated vasoconstriction but also by potentiating vasodilation at plasma Hb concentrations of <25 muM. We also observed an interaction between plasma Hb levels and nitrite to augment nitroprusside-induced vasodilation of the pulmonary and systemic circulation. This nitrite reductase activity of Hb in vivo was recapitulated in vitro using a mitochondrial NO sensor system. Nitrite infusions may promote NO generation from Hb while maintaining oxygen delivery; this effect could be harnessed to treat hemolytic conditions and to detoxify Hb-based blood substitutes.     

Catalytic generation of N2O3 by the concerted nitrite reductase and anhydrase activity of hemoglobin

Nitrite reacts with deoxyhemoglobin to form nitric oxide (NO) and methemoglobin. Though this reaction is experimentally associated with NO generation and vasodilation, kinetic analysis suggests that NO should not be able to escape inactivation in the erythrocyte. We have discovered that products of the nitrite-hemoglobin reaction generate dinitrogen trioxide (N2O3) via a novel reaction of NO and nitrite-bound methemoglobin. The oxygen-bound form of nitrite-methemoglobin shows a degree of ferrous nitrogen dioxide (Fe(II)-NO2*) character, so it may rapidly react with NO to form N2O3. N2O3 partitions in lipid, homolyzes to NO and readily nitrosates thiols, all of which are common pathways for NO escape from the erythrocyte. These results reveal a fundamental heme globin- and nitrite-catalyzed chemical reaction pathway to N2O3, NO and S-nitrosothiol that could form the basis of in vivo nitrite-dependent signaling. Because the reaction redox-cycles (that is, regenerates ferrous heme) and the nitrite-methemoglobin intermediate is not observable by electron paramagnetic resonance spectroscopy, this reaction has been 'invisible' to experimentalists over the last 100 years.     

Dexamethasone alters arachidonate release from human epithelial cells by induction of p11 protein synthesis and inhibition of phospholipase A2 activity.

The effect of the glucocorticosteroid, dexamethasone, on arachidonic acid (AA) release and on protein levels of p11 and cytosolic phospholipase A2 (cPLA2) was studied in two epithelial cell lines, HeLa cells and BEAS-2B cells. Dexamethasone treatment of HeLa cells and BEAS-2B cells increased cellular p11 protein and mRNA levels in a time- and dose-dependent manner. It had little effect on levels of cPLA2 protein. In order to determine if increased p11 protein expression resulted in increased interaction between p11 and cPLA2, anti-cPLA2 antibodies were used to immunoprecipitate p11.cPLA2 complexes and Western blots of the immunoprecipitate were used to detect p11. In cells treated with dexamethasone, more p11 was detected in the anti-cPLA2 immunoprecipitate compared with control cells. Dexamethasone treatment of HeLa cells prelabeled with [3H]AA decreased the release of [3H]AA under basal conditions and after stimulation with the calcium ionophore A23187 (10(-6) M). In order to determine if altering the p11 protein levels in HeLa cells independent of glucocorticosteroid treatment could also produce an effect on [3H]AA release, cells were stably transfected with plasmids expressing either p11 antisense mRNA or p11 mRNA. Cloned HeLa cells expressing p11 antisense mRNA exhibited less cellular p11 protein compared with control cells and greater [3H]AA release compared with cells transfected with a control vector. Cloned HeLa cells stably transfected with a p11 expression vector exhibited increased p11 cellular protein and diminished [3H]AA release under basal conditions and in response to A23187. Therefore, dexamethasone alteration of epithelial cell AA release may be due in part to induction of p11 protein expression.     

Genetic signature of the colonisation dynamics along a coastal expansion front in the damselfly Coenagrion scitulum

1. Many insects are expanding their distribution range polewards as a result of climate change, which has been shown to be associated with founder effects leading to a reduction in genetic diversity and an increase in genetic differentiation. These spatial genetic patterns may arise from colonisation from a broad expansion front or a limited neighbourhood after a stepping stone model of dispersal. The temporal persistence of such founder effects are poorly understood, mainly because studies looking at the fine‐scale initial temporal dynamics of the genetic signature of a range expansion are rare. 2. Using microsatellite markers, we performed a detailed spatiotemporal genetic analysis of the range expanding damselfly Coenagrion scitulum (Rambur) along a coastal axis during the first years after colonisation. 3. A decrease was in (private) allelic richness when going northwards along the coastline, which is consistent with a scenario of cumulative founder events. In spite of the spatiotemporal dynamics in the observation records of the species along the coastline, the spatial genetic data indicated a major contribution from the broad expansion front during the colonisation of the coastline rather than a stepping‐stone colonisation process. 4. The fine‐scale temporal dynamics of the range expansion indicated the absence of persistent founder effects and instead showed considerable temporal instability in genetic indices at the more northern edge populations. This may be explained by genetic immigration and admixture from the broad expansion front in this active disperser.     

Arabidopsis thaliana ASN2 encoding asparagine synthetase is involved in the control of nitrogen assimilation and export during vegetative growth

We investigated the function of ASN2, one of the three genes encoding asparagine synthetase (EC 6.3.5.4), which is the most highly expressed in vegetative leaves of Arabidopsis thaliana. Expression of ASN2 and parallel higher asparagine content in darkness suggest that leaf metabolism involves ASN2 for asparagine synthesis. In asn2‐1 knockout and asn2‐2 knockdown lines, ASN2 disruption caused a defective growth phenotype and ammonium accumulation. The asn2 mutant leaves displayed a depleted asparagine and an accumulation of alanine, GABA, pyruvate and fumarate, indicating an alanine formation from pyruvate through the GABA shunt to consume excess ammonium in the absence of asparagine synthesis. By contrast, asparagine did not contribute to photorespiratory nitrogen recycle as photosynthetic net CO₂ assimilation was not significantly different between lines under both 21 and 2% O₂. ASN2 was found in phloem companion cells by in situ hybridization and immunolocalization. Moreover, lack of asparagine in asn2 phloem sap and lowered ¹⁵N flux to sinks, accompanied by the delayed yellowing (senescence) of asn2 leaves, in the absence of asparagine support a specific role of asparagine in phloem loading and nitrogen reallocation. We conclude that ASN2 is essential for nitrogen assimilation, distribution and remobilization (via the phloem) within the plant.     

Initiation of Cellulose Biosynthesis

IN spite of much investigation the problem of the molecular mechanism of cellulose synthesis remains unsolved¹. Hexose phosphates², sugar nucleotides^3–6 and a glycolipid^7–9 have been suggested as the precursor of cellulose. Implicit in all these investigations is the supposition that a single substrate suffices for the synthesis. We describe here some preliminary observations which seem to throw new light on the possible mechanism.