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.     

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.     

Chemical composition and antimicrobial activity of the essential oils of Anthospermum emirnense and Anthospermum perrieri (Rubiaceae)

The essential oils of Anthospermum emirnense Baker and Anthospermum perrieri Homolle ex Puff, obtained by hydrodistillation in 0.03 and 0.02% yield, respectively, were analyzed by GC/MS. In both cases, the major constituents consisted of sesquiterpene hydrocarbons and oxygenated sesquiterpenes. The two species showed an important qualitative similarity, with 40 compounds common to A. emirnense and A. perrieri, including β-elemene, trans-β-caryophyllene, caryophyllene oxide, and τ-cadinol, which were major components in both cases. When tested for antimicrobial activity, both essential oils showed similar profiles and exhibited interesting minimal-inhibitory-concentration (MIC) values towards Bacillus subtilis, Chryseobacterium indologenes, Flavimonas oryzihabitans, and Yersinia enterocolitica.     

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.     

1H, (13)C, and (15)N NMR stereochemical study of cis-fused 7a(8a)-methyl and 6-phenyl octa(hexa)hydrocyclopenta[d][1,3]oxazines and [3,1]benzoxazines

Four 7a-methyl octa(or hexa)hydrocyclopenta[d][1,3]oxazines, five 8a-methyl octa(or hexa)hydro[3,1]benzoxazines, two 6-phenyl hexahydro[3,1]benzoxazinones, and 8a-methyl hexahydro[1,3]benzoxazinone, all cis-fused, were prepared and their stereostructures studied by various one- and two-dimensional (1)H, (13)C, and (15)N NMR spectroscopic methods. In solution, the cyclopentane-fused 2-oxo derivatives and the 1,3-benzoxazinone were found to attain exclusively the N-in/O-in conformation, whereas the 6-phenyl 2-oxo/thioxo derivatives were found to be present predominantly in the N-out conformation. The C-2 unsubstituted and the 2-oxo/thioxo 7a/8a-methyl derivatives were all present in solution as a rapidly interconverting equilibrium of the N-in and N-out conformations. The C-2 methyl derivatives were each found to be interconvertable mixtures of epimers (at C-2) with the N-in conformer predominating for one epimer and the N-out conformer predominating for the other, with both predominating conformers having the C-2 methyl group equatorially orientated. The substituent on the nitrogen (H or Me) was found to be always predominantly equatorial with respect to the heteroring, except for the epimeric 2-methyl derivatives with N-out conformations where steric constraints and the generalized anomeric effect resulted in the axial orientation of the C-2 methyl being favored.     

Isolation and cross‐familial amplification of 41 microsatellites for the brook charr (Salvelinus fontinalis)

The brook charr (Salvelinus fontinalis; Osteichthyes: Salmonidae) is a phenotypically diverse fish species inhabiting much of North America. But relatively few genetic diagnostic resources are available for this fish species. We isolated 41 microsatellites from S. fontinalis polymorphic in one or more species of salmonid fish. Thirty‐seven were polymorphic in brook charr, 15 in the congener Arctic charr (Salvelinus alpinus) and 14 in the lake charr (Salvelinus namaycush). Polymorphism was also relatively high in Oncorhynchus, where 21 loci were polymorphic in rainbow trout (Oncorhynchus mykiss) and 16 in cutthroat trout (Oncorhynchus clarkii) but only seven and four microsatellite loci were polymorphic in the more distantly related lake whitefish (Coregonus clupeaformis) and Atlantic salmon (Salmo salar), respectively. One duplicated locus (Sfo228Lav) was polymorphic at both duplicates in S. fontinalis.