Respiration and Phloem Translocation in the Roots of Chickpea (Cicer arietinum)

Root growth in chickpea (Cicer arietinum) has been studied fromthe early vegetative phase to the reproductive stage in orderto elucidate its growth and maintenance respiration and to quantifythe translocation of assimilates from shoot to root. A carbonbalance has been drawn for this purpose using the growth andrespiration data. The increase in the sieve tube cross-sectionalarea was also followed simultaneously. Plants growing in a nutrient culture medium were studied todetermine the relative growth rate (RGR) 5–60 d aftergermination. RGR declined from 113 to 41 mg d^–1 g^–1during the measurement period. Simultaneous with the RGR analysis,respiration rate was also measured using an oxygen electrode.The respiration rate declined as the plants aged and a drasticreduction was recorded following anthesis. The relationshipbetween RGR and respiration rate was used to extrapolate themaintenance respiration (m) and growth respiration (1/Y_EG).The respiration quotient (r.q.) of the roots was 1.2 and theQ₁₀ in the range 20–25 °C was 2·2. A carbon balance for the roots was constructed by subtractingthe carbon lost during respiration from that gained during growth.The roots were found to respire no less than 80% of the carbontranslocated. The increase in the cross-sectional area composed of sieve tubeswas measured near the root-shoot junction as the plants grew.Chickpea has storied sieve plates which simplifies these measurements.Their cross-sectional area increased during growth mainly becauseof an increase in sieve tube number. The diameter of individualsieve tubes remained constant. Specific mass transfer (SMT) values for seive tubes into theroots have been computed during various stages of growth. SMTvalues were relatively constant before anthesis (approx. 6·5g h^–1 cm^–2), but decreased following anthesis. Wedid not evaluate possible retranslocation from roots: any suchretranslocation would have the effect of increasing our SMTvalues. Chickpea, Cicer arietinum, legume, root, respiration, phloem, translocation, carbon balance, specific mass transfer, sieve-tube dimensions     

Analysis of plastid DNA-like sequences within the nuclear genomes of higher plants

A wide-ranging examination of plastid (pt)DNA sequence homologies within higher plant nuclear genomes (promiscuous DNA) was undertaken. Digestion with methylation-sensitive restriction enzymes and Southern analysis was used to distinguish plastid and nuclear DNA in order to assess the extent of variability of promiscuous sequences within and between plant species. Some species, such as Gossypium hirsutum (cotton), Nicotiana tabacum (tobacco), and Chenopodium quinoa, showed homogenity of these sequences, while intraspecific sequence variation was observed among different cultivars of Pisum sativum (pea), Hordeum vulgare (barley), and Triticum aestivum (wheat). Hypervariability of plastid sequence homologies was identified in the nuclear genomes of Spinacea oleracea (spinach) and Beta vulgaris (beet), in which individual plants were shown to possess a unique spectrum of nuclear sequences with ptDNA homology. This hypervariability apparently extended to somatic variation in B. vulgaris. No sequences with ptDNA homology were identified by this method in the nuclear genome of Arabidopsis thaliana.      

Incidence and levels of fumonisin contamination in Colombian corn and corn products

A survey was conducted to determine the levels of fumonisins B1 and B2 in corn and corn-based products available in Colombia for human and animal consumption. A total of 120 samples were analyzed by acetonitrile-water extraction, cleanup with a strong-anion-exchange column, and liquid chromatography with o-phthaldialdehyde-2-mercaptoethanol derivatization and fluorescence detection. The samples of corn and corn-based products for animal intake were taken at different feed manufacturing plants, whereas the samples used for human foods where purchased from local retail stores. The number of positive samples for fumonisin B1 was 20.0% higher in corn and corn-based products for animal intake (75.0%) than in corn and corn-based products for human consumption (55.0%). The levels of fumonisin B1 were also higher in corn and corn-based products for animal intake (mean = 694 μg/kg; range = 32–2964 μg/kg), than in corn and corn-based products for human intake (mean = 218 μg/kg; range = 24–2170 μg/ kg). The incidence and levels of fumonisin B2 were lower than those for fumonisin B1. Corn and corn-based products for animal consumption had an incidence of fumonisin B2 of 58.3%, with a mean value of 283 μg/kg, and a range of 44–987 μg/kg. The incidence of fumonisin B2 in corn-based products for human intake was 35.0%, with a mean value of 118 μg/kg and a range of 21–833 μg/kg. The highest incidence and levels of fumonisins were found in samples of hominy feed, with concentrations ranging from 86 to 2964 μg/kg fumonisin B1 and 57 to 987 μg/kg fumonisin B2.     

Sap Ascent in Vascular Plants: Challengers to the Cohesion Theory Ignore the Significance of Immature Xylem and the Recycling of Munch Water

In recent years the cohesion theory has been attacked on thegrounds that direct measurements made with the pressure probeindicate that sap tensions are much less (maximum tension approx.0.7 MPa) than indicated by parallel measurements made with themore conventional methods: osmotic methods, pressure bomb, orpsychrometer. It has also been claimed that other direct methodsdo not support the cohesion theory. Thus a re-examination usingthe Renner technique indicated sap tensions of approx. 2.5 MPa.Also an independent method based on mercury penetrometry providesevidence that sap tensions of at least 2.0 MPa can be demonstrateddirectly implying, that serious limitations arise from the pressureprobe method itself. Without tensions exceeding 2.0 MPa mangroveswould be unable to extract fresh water for transpiration fromseawater. It is suggested that the pressure probe is susceptibleto bias because it investigates the least mature xylem conduitswhile they are still under varying degrees of turgor pressureand only partially interconnected with the main xylem system.This supposition is supported by claims that the xylem sap sampledby the probe contains significant concentrations of solutes.Additionally water, supplied by reverse osmosis from the sievetubes (‘Münch water’), is continually beingliberated in the vicinity of the outermost xylem vessels hydratingthem to an atypical degree which can explain several of thediscrepancies claimed. These results, which are supported bythe work of others, demonstrate that the challenges to the cohesiontheory for the ascent of sap are ill-founded. The release ofwater from the phloem can explain not only some discrepanciesclaimed by the cohesion challengers, but also explain the refillingof cavitated xylem conduits: a hitherto unsuspected role forthe phloem transport system. Cohesion theory; sap ascent; cavitation; pressure probe; xylem transport; vessel development; recycled water; reverse osmosis     

An Ideal Viscous Flow Porometer

A new design of viscous flow porometer is described which isbased on the pronciple of air suction into a syringe which thenmeasures the volume of air atmosphere pressure. This porometerallows accurate readings to be made on the 0-100 scale on thesyringe barrel when the piston has returned following its release.Each reading takes only seconds to make so that data can becollected for statistical analysis before stomata change inaperture and with minimal interference with the leaf envirnionment.Calibiration procedures are described: examples ofthe new porometersand also silicone rubber imprints support the validity of measurementsmade by the new porometer.     

Frasnian vertebrate taphonomy and sedimentology of macrofossil concentrations from the Langsēde Cliff,Latvia

Luk?evi?s, E., Ahlberg, P.E., Stinkulis, ?., Vasi?kova, J. & Zupi??, I. 2011: Frasnian vertebrate taphonomy and sedimentology of macrofossil concentrations from the Langsēde Cliff, Latvia. Lethaia, Vol. 45, pp. 356–370. The siliciclastic sequence of the Upper Devonian of Kurzeme, Western Latvia, is renowned for abundant vertebrate fossils, including the stem tetrapods Obruchevichthys gracilis and Ventastega curonica. During the first detailed taphonomic study of the vertebrate assemblage from the Ogre Formation cropping out at the Langsēde Cliff, Imula River, abundant vertebrate remains have been examined and identified as belonging to one psammosteid, two acanthodian and three sarcopterygian genera; the placoderm Bothriolepis maxima dominates the assemblage. Besides fully disarticulated placoderm and psammosteid plates, separate sarcopterygian scales and teeth, and acanthodian spines, partly articulated specimens including complete distal segments of Bothriolepis pectoral fins, Bothriolepis head shields and sarcopterygian lower jaws have been found. The size distribution of the placoderm bones demonstrates that the individuals within the assemblage are of approximately uniform age. Distinct zones have been traced within the horizontal distribution of the bones. These linear zones are almost perpendicular to the dominant dip azimuth of the cross‐beds and ripple‐laminae and most probably correspond to the depressions between subaqueous dunes. Concavity ratio varies significantly within the excavation area. The degree of fragmentation of the bones and disarticulation of the skeletons suggest that the carcasses were reworked and slightly transported before burial. Sedimentological data suggest deposition in a shallow marine environment under the influence of rapid currents. The fossiliferous bed consists of a basal bone conglomerate covered by a cross‐stratified sandstone with mud drapes, which is in turn overlain by ripple laminated sandstone, indicating the bones were buried by the gradual infilling of a tidal channel. All the Middle–Upper Devonian vertebrate bone‐beds from Latvia are associated with sandy to clayey deposits and have been formed in a sea‐coastal zone during rapid sedimentation episodes, but differ in fossil abundance and degree of preservation. □Agnathans, Devonian, facies analysis, fish, fossil assemblage, palaeoenvironment.     

A tree-based method for the rapid screening of chemical fingerprints

Background  

The fingerprint of a molecule is a bitstring based on its structure, constructed such that structurally similar molecules will have similar fingerprints. Molecular fingerprints can be used in an initial phase of drug development for identifying novel drug candidates by screening large databases for molecules with fingerprints similar to a query fingerprint.