Effects of inbred/outbred crosses on progeny sex ratio in Silene latifolia (Caryophyllaceae)

Sex ratio polymorphism has been extensively studied in Silene latifolia, but it is neither known whether inbreeding (which is likely to occur under field conditions) affects it, nor which of the proposed mechanisms (Y degeneration, X-linked drive) is more important. Both mechanisms predict reduced pollen performance. In this study, females were crossed with pollen from related and unrelated males in single-donor and two-donor crosses, and the sex ratio of offspring (n = 866, 60 crosses), sons'in vitro pollen germination and sex ratios in parental families were scored. Flowers receiving only unrelated pollen produced a significant excess of sons. Sex ratios were not significantly correlated between generations. Sons'in vitro pollen germination was significantly negatively correlated with the 'sex-ratio phenotype' of maternal grandfathers, but not of fathers. This generation leap may be consistent with X-linked determinants because Y-linked determinants alone cannot explain it (grandfathers, fathers and sons share the same Y chromosome). Further work is required, but inbreeding and limited dispersal may lead to local accumulation of biasing factors, a process potentially countered by conditional shifts to produce more sons in pure outbred crosses.     

Regioselective formation of quercetin 5-O-glucoside from orally administered quercetin in the silkworm, Bombyx mori

The cocoons of some races of the silkworm, Bombyx mori, have been shown to contain 5-O-glucosylated flavonoids, which do not occur naturally in the leaves of their host plant, mulberry (Morus alba). Thus, dietary flavonoids could be biotransformed in this insect. In this study, we found that after feeding silkworms a diet rich in the flavonol quercetin, quercetin 5-O-glucoside was the predominant metabolite in the midgut tissue, while quercetin 5,4'-di-O-glucoside was the major constituent in the hemolymph and silk glands. UDP-glucosyltransferase (UGT) in the midgut could transfer glucose to each of the hydroxyl groups of quercetin, with a preference for formation of 5-O-glucoside, while quercetin 5,4'-di-O-glucoside was predominantly produced if the enzyme extracts of either the fat body or silk glands were incubated with quercetin 5-O-glucoside and UDP-glucose. These results suggest that dietary quercetin was glucosylated at the 5-O position in the midgut as the first-pass metabolite of quercetin after oral absorption, then glucosylated at the 4'-O position in the fat body or silk glands. The 5-O-glucosylated flavonoids retained biological activity in the insect, since the total free radical scavenging capacity of several tissues increased after oral administration of quercetin.     

Isolation and characterization of 21 microsatellite markers in the barn owl (Tyto alba)

We report 21 new polymorphic microsatellite markers in the European barn owl (Tyto alba). The polymorphism of the reported markers was evaluated in a population situated in western Switzerland and in another from Tenerife, Canary Islands. The number of alleles per locus varies between two and 31, and expected heterozygosity per population ranges from 0.16 to 0.95. All loci are in Hardy-Weinberg equilibrium and no linkage disequilibrium was detected. Two loci exhibit a null allele in the Tenerife population.     

Pitfalls in determining size homoplasy of microsatellite loci

Size homoplasy of microsatellite loci can be detected by single‐strand conformation polymorphism analysis (SSCP) or sequence analysis. The present note demonstrates pitfalls of sequencing microsatellite loci. A complex chloroplast microsatellite locus was polymerase chain reaction (PCR) amplified from 33 Abies alba individuals, and the products cloned and sequenced. After 2–7 clones per individual had been sequenced and aligned, differences in repeat numbers occurred among clones of the same individual. It was concluded that the DNA polymerase slippage during PCR most probably caused this variation. A solution specific to the analysed complex locus was found by splitting it into two new loci.     

Poplar PtabZIP1‐like enhances lateral root formation and biomass growth under drought stress

Developing drought‐resistance varieties is a major goal for bioenergy crops, such as poplar (Populus), which will be grown on marginal lands with little or no water input. Root architecture can affect drought resistance, but few genes that affect root architecture in relation to water availability have been identified. Here, using activation tagging in the prime bioenergy crop poplar, we have identified a mutant that overcomes the block of lateral root (LR) formation under osmotic stress. Positioning of the tag, validation of the activation and recapitulation showed that the phenotype is caused by the poplar PtabZIP1‐like (PtabZIP1L) gene with highest homology to bZIP1 from Arabidopsis. PtabZIP1L is predominantly expressed in roots, particularly in zones where lateral root primordia (LRP) initiate and LR differentiate and emerge. Transgenics overexpressing PtabZIP1L showed precocious LRP and LR development, while PtabZIP1L suppression significantly delayed both LRP and LR formation. Transgenic overexpression and suppression of PtabZIP1L also resulted in modulation of key metabolites like proline, asparagine, valine and several flavonoids. Consistently, expression of both of the poplar Proline Dehydrogenase orthologs and two of the Flavonol Synthases genes was also increased and decreased in overexpressed and suppressed transgenics, respectively. These findings suggest that PtabZIP1L mediates LR development and drought resistance through modulation of multiple metabolic pathways.     

Carbon dioxide transport inxylem causes errors in estimation of rates of respiration in stemsand branches of trees

Complementary laboratory and field experiments showed that theinternal transport of carbon dioxide (CO₂) in the xylemof trees is an important pathway for carbon movement. Carbon dioxidereleased by respiration dissolves in sap and moves upward in thetranspirational stream. The concentration of CO₂ in xylemsap can be up to three orders of magnitude greater than that foundin the atmosphere. In the present experiments, diffusion outwardof a portion of xylem‐transported CO₂ caused a substantialoverestimation of the apparent rate of stem and branch respiration.Rates of CO₂ efflux were linearly related to sap CO₂ concentration.Direct manipulations of xylem sap CO₂ concentration producedrapid and reversible changes in CO₂ efflux from stemsand branches, in some cases quadrupling the rate of efflux. Theseresults demonstrated that apparent rates of stem and branch respirationof trees are in large part a by‐product of the rate of CO₂ diffusionfrom xylem sap.     

A new large barn owl (Aves, Strigiformes, Tytonidae) from the Middle Pleistocene of Sicily, Italy, and its taphonomical significance

A new species of Tytonidae, Tyto mourerchauvireae, is described from the Sicilian cave deposits of Spinagallo, Luparello and Marasà, which have yielded a common vertebrate fossil assemblages referred to the early Middle Pleistocene. T. mourerchauvireae nov. sp. shows a pronounced increase in body size compared to other congeneric taxa. It is larger than the extant Tyto alba and the extinct Tyto balearica and Tyto sanctialbani and comparable in size among the Mediterranean taxa only with the extinct Tyto robusta, which differs in some morphological characteristics of the long bones. The insular adaptations of T. mourerchauvireae nov. sp. and the differences from the other forms of the genus Tyto which spread through the Mediterranean area during Neogene and Pleistocene are discussed. The fossil assemblages of the early Middle Pleistocene of Sicily are dominated by extinct giant Gliridae of the genus Leithia and Maltamys; these taxa are regarded as the primary prey items of T. mourerchauvireae nov. sp. The Gliridae remains were analysed microscopically to detect possible modifications of bones and teeth caused by ingestion and digestion processes. This type of analysis, together with the qualitative study of the fossil assemblages, allows to show the taphonomical importance of T. mourerchauvireae nov. sp. as agent of accumulation in such Sicilian fossil assemblages. Incidentally the taxonomic validity of T. robusta is discussed and confirmed.     

Root system architecture and gravity perception of a mangrove plant,Sonneratia alba J. Smith

We describe the features of the root system and the gravitropism of roots produced bySonneratia alba. The root system consists of four root types with different growth directions: (a) Pneumatophores, which are negatively orthogravitropic and their statocytes are very large (922 μm²) and the statolith is located near the proximal wall, (b) Cable roots and (c) Feeding roots which are both diagravitropic and their statoliths are settled along the longitudinal wall, and (d) Anchor roots which are positively orthogravitropic. The statocyte cells are the smallest (420 μm²) and statoliths settled at the distal wall. We found that all roots with marked gravitropism have statoliths that settle along different walls of the statocyte. This implies that the statoliths sensing of gravity is done by gravity on mass, and that they are denser than surrounding cytoplasm and this position is related to root growth direction. This finding matches the statoliths sediment under the effect of gravity. Irrespective of statolith, position and direction of growth may be stable.     

Efficient plantlet regeneration from protoplasts isolated from suspension cultures of poplar (Populus alba L.)

We developed an efficient plant regeneration system from protoplasts for poplar (Populus alba L.). Protoplasts were isolated from 4-day-old suspension cultures derived from seed-induced calli with a yield of 6.96× 10⁶ cells/g fresh weight cells and then cultured at a concentration of 2.5×10⁵ cells/ml in NH₄NO₃-free Murashige and Skoog (MS) medium supplemented with 5 μM 2,4-dichlorophenoxyacetic acid (2,4-D), 0.05 μM thidiazuron (TDZ) and 0.5 M glucose as a osmoticum. The plating efficiency of the cultured protoplasts was calculated at 26.5% at day 7 and 31.7% at day 14. Cell colonies were observed after culturing for 4 weeks. Regenerated colonies were propagated through subculture in liquid MS medium supplemented with 5 μM 2,4-D. Buds were induced from regenerated calli on MS medium containing 10 μM kinetin or 1 μM TDZ. Regenerated shoots were rooted on half-strength MS medium, and the plantlets were transplanted in soil. Randomly amplified polymorphic DNA analysis did not detect any DNA polymorphism among the regenerated plants. Received: 7 March 1997 / Revision received: 16 June 1997 / Accepted: 5 July 1997