MORPHOLOGY OF TEOSINTOID AND TRIPSACOID MAIZE (ZEA MAYS L.)

Modern races of maize (Zea mays L.) are characterized by indurated glume and rachis tissues. The archaeological record, as well as experimental studies indicate that in North America this induration is associated with hybridization between domesticated maize and its closest wild relative Z. mays subsp. mexicana (Schrad.) Iltis (teosinte). Similar induration can also be introduced into maize through introgression from Tripsacum. North and South American indurated races of maize are not all closely allied morphologically. They evolved independently under domestication. Teosinte is absent from South America, but Tripsacum is widely sympatric with maize from about 42 N to 42 S latitude. For these reasons it has been postulated that induration in South American races may be the result of Tripsacum introgression. However, barriers restricting gene exchange between Zea and Tripsacum are difficult to overcome in nature. It is maintained that indurated South American races of maize were derived from indurated Mexican races, and that the presence or absence of such induration is due to different degrees of expression by intermediate alleles of the tunicate locus.     

A mutation (R826W) in nucleotide-binding domain 1 of ABCC8 reduces ATPase activity and causes transient neonatal diabetes

Activating mutations in the pore-forming Kir6.2 (KCNJ11) and regulatory sulphonylurea receptor SUR1 (ABCC8) subunits of the K(ATP) channel are a common cause of transient neonatal diabetes mellitus (TNDM). We identified a new TNDM mutation (R826W) in the first nucleotide-binding domain (NBD1) of SUR1. The mutation was found in a region that heterodimerizes with NBD2 to form catalytic site 2. Functional analysis showed that this mutation decreases MgATP hydrolysis by purified maltose-binding protein MBP-NBD1 fusion proteins. Inhibition of ATP hydrolysis by MgADP or BeF was not changed. The results indicate that the ATPase cycle lingers in the post-hydrolytic MgADP.P(i)-bound state, which is associated with channel activation. The extent of MgADP-dependent activation of K(ATP) channel activity was unaffected by the R826W mutation, but the time course of deactivation was slowed. Channel inhibition by MgATP was reduced, leading to an increase in resting whole-cell currents. In pancreatic beta cells, this would lead to less insulin secretion and thereby diabetes.     

A cycad's non‐saturating response to carbon dioxide enrichment indicates Cenozoic carbon limitation in pre‐historic plants

Cycads were a dominant plant functional type during the Mesozoic Era when atmospheric carbon dioxide [CO₂] greatly exceeded current conditions. Cycads, now rare and endangered, are slow‐growing perennial gymnosperms that develop carbon‐rich structural biomass, such as sclerophyllous leaves, dense stems and massive reproductive cones. Is cycad carbon partitioning to specific organs a constraint of their high [CO₂] evolutionary history (CO₂ legacy hypothesis, CLH)? To explore changes in cycad growth, carbon partitioning and assimilation responses that could be expected during the CO₂ depletion of the Cenozoic Era, individuals of the cycad species Encephalartos villosus plants were grown at four CO₂ levels: 400, 550, 750 and 1000 μmol mol^?1. The CLH predicts that cycad biomass and growth rates would increase in elevated [CO₂] due to increased net assimilation rates, and that carbon‐dense structures would provide sufficient carbohydrate sinks to prevent photosynthetic down‐regulation even under super‐ambient [CO₂] of 1000 μmol mol^?1. Both hypotheses were confirmed, though the latter less strongly. Plant relative growth rates increased 23% and biomass accumulation increased 65% in 1000 μmol mol^?1relative to 400 μmol mol^?1 treatment groups. Mean net assimilation rates increased 130% at 1000 μmol mol^?1 relative to 400 μmol mol^?1 CO₂, though there was some down‐regulation of maximum rate of carboxylation (Vc_max). Assimilation rates, relative growth rates, biomass and mean leaf sugar content were linearly related to [CO₂] over the entire experimental range. Photosynthesis appears to be regulated by stomata at low CO₂ levels and by non‐stomatal (i.e. biochemical limitations) at greater concentrations. In general, our results suggest that growth and physiological performance of cycads have been severely compromised by declining [CO₂] during the Cenozoic Era, possibly contributing to the current rare and endangered status of this functional type.     

Characterization of a family 54 α-<Emphasis Type="SmallCaps">l</Emphasis>-arabinofuranosidase from <Emphasis Type="Italic">Aureobasidium pullulans</Emphasis>

A glycosyl hydrolase family 54 (GH54) α-l-arabinofuranosidase gene (abfA) of Aureobasidium pullulans was amplified by polymerase chain reaction from genomic DNA and a 498-amino-acid open reading frame deduced from the DNA sequence. Modeling of the highly conserved A. pullulans AbfA protein sequence on the crystal structure of Aspergillus kawachii AkabfB showed that the catalytic amino acid arrangement and overall structure were highly similar including the N-terminal catalytic and C-terminal arabinose binding domains. The abfA gene was expressed in Saccharomyces cerevisiae, and the heterologous enzyme was purified. The protein was monomeric, migrating at 49 kDa on sodium dodecyl sulfate-polyacrylamide gel electrophoresis and eluting at 36 kDa upon gel filtration. AbfA showed maximal activity at 55°C and between pH 3.5 and pH 4. The enzyme had a K _m value for p-nitrophenyl-α-l-arabinofuranoside of 3.7 mM and a V _max of 34.8 μmol min⁻¹ mg protein⁻¹. Arabinose acted as a noncompetitive inhibitor with a K _i of 38.4 mM. The enzyme released arabinose from maize fiber, oat spelt arabinoxylan, and wheat arabinoxylan, but not from larch wood arabinogalactan or α-1,5-debranched arabinan. AbfA displayed low activity against α-1,5-l-arabino-oligosaccharides. The enzyme acted synergistically with endo-β-1,4-xylanase in the breakdown of wheat arabinoxylan. Binding of AbfA to xylan from several sources confirmed the presence of a functional carbohydrate-binding module. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Domestication of mawa millet (Echinochloa colona)

Two species of Echinochloa are grown as cereals. Echinochloa crusgalli is native to temperate Eurasia and was domesticated in Japan some 4,000 yr ago. Echinochloa colona is widely distributed in the tropics and subtropics of the Old World. It was domesticated in India. Echinochloa colona is morphologically allied to E. crusgalli, but hybrids between them are sterile. Echinochloa colona differs consistently from E. crusgalli in having smaller spikelets with membran-aceous rather than chartaceous glumes. Hybrids between wild and cultivated taxa of E. colona and between those of E. crusgalli are fertile. Cultivated E. colona is variable. It is grown as a cereal across India, Kashmir and Sikkim. Four morphological races are recognized, although these do not have geographical, ecological or ethnological unity. Race laxa is confined to Sikkim where races robusta, intermedia and stolonifera are also grown. In India, races robusta, intermedia and stolonifera are often grown as mixtures, and Echinochloa is sometimes grown as a mixture with other cereals, particularly Setaria italica (foxtail millet) or Eleusine coracana (finger millet). The species is planted on poor soil, and some cultivars mature in less than 2 mo. They hold considerable promise as cereals for the semiarid tropics.     

Seed proteins and systematics of Tripsacum

The genus Tripsacum (Gramineae) is distributed between the latitude 42°N and 24°S in the New World. It is divided into two sections. Section Tripsacum includes 11 species with T. dectyloides (L) L. extending across the range of the genus. Section Fasciculata includes five Meso-American species with T. lanceolatum Rupr. ex Fourn. extending into southern Arizona. The genus displays considerable diversity in seed proteins. Variation patterns are of limited use in distinguishing sections, but are species and habitat specific. Protein data are particularly useful in subspecific classification, and consistently distinguish diploid from polyploid races of T. zopilotense Hern. and Randolph and T. bravum Gray. The tetraploid ectotype of T. bravum deserves specific rank and the robust ecotype of T. dactyloides var. meridonate de Wet and Timothy deserves varietal rank.     

Effect of Various Mixtures of Diethylether, Halothane, Nitrous Oxide and Oxygen on Low Molecular Weight Iron Content and Mitochondrial Function of the Rat Myocardium

Anaesthetic drugs can induce reversible as well as irreversible changes in cell membranes and intracellular proteins as well as lipid peroxidation in the liver. Low molecular weight iron species (LMWI) can by their catalytic activity contribute to the generation of free radicals (hydroxyl radicals). Free radicals are a recognisable cause of intracellular damage. Impaired mitochondrial function is also a sign of intracellular damage, which is usually irreversible. Thus, an agent may be cytotoxic when it causes a significant increase in intracellular LMWI. Whether the LMWI arise from ferritin or is released from iron containing proteins, the same reaction occurs. As long as LMWI can undergo redox cycling, hydroxyl radicals can be formed. We investigated the effect of various mixtures of diethylether, halothane, nitrous oxide and oxygen on the intracellular LMWI content and mitochondrial function of the rat myocardium.

Hearts isolated from rats anaesthetised with diethylether showed an increase in the cytosolic LMWI compared to the control group. No increase in mitochondrial LMWI was demonstrated. Subsequent perfusion of the isolated hearts showed a further increase in the LMWI. On perfusion the mitochondrial LMWI increased in comparison with controls. Mitochondrial function was significantly impaired as measured by the QO₂ (state 3), ADP/O ratio and oxidative phosphorylation rate (OPR).

Exposure of rats to 50% nitrous oxide for 15 minutes increased the myocardial LMWI, but had no effect on mitochondrial function. Exposure to room air for 30 minutes before isolating the hearts, still showed a significant increase in LMWI with no detectable change in mitochondrial function.

Halothane, on the other hand, did not have an effect on the myocardial LMWI and mitochondrial function in the experiment setup used. We therefore concluded that diethylether and nitrous oxide are potentially toxic to the myocardium and may potentiate the action of free radicals.