Assessing internal epicormic dynamics in Quercus alba L. using CT scanning: the strong effects of shoot development and tree growth relative to progeny level genetic variation

Epicormic branches can be a serious silvicultural problem in many Quercus species because of the potential reduction in log value associated with their occurrence. The phenomenon is also problematic for tree improvement since the genetic component of epicormic branching has not been well quantified. The strong influence of ontogeny on epicormic development in Quercus is well established; however, the long-standing assumption that genetic variation also influences epicormics has not been rigorously tested. With trees from two, 25-year-old Quercus alba L. progeny tests in IN, USA, we used computed tomography scanning to characterize internal epicormic development. We sampled trees from upper and lower crown classes of families that had been classified as having low, medium and high numbers of epicormic sprouts. We also measured an array of variables related to growth and competition with the objective of assessing the relative impacts of genetics and vigor on epicormic development. Using generalized linear and linear mixed models, we found that ontogenetic and vigor variables were strongly associated with epicormic structure and development, and that the genetic effect was negligible. The total number of epicormics was most significantly influenced by the number of sequential branches that bore epicormics (p < 0.001) and the proportion of undeveloped epicormics was most significantly influenced by diameter increment (p < 0.001). We propose that a strong focus on individual tree vigor and form in tree improvement could minimize the impact of epicormic branching in Q. alba trees.     

Solvent influence on model oxidations of alpha-tocopherol

(+/-)-alpha-Tocopherol has been oxidised with t-butyl hydroperoxide in chloroform in order to simulate in vivo oxidations due to lipid hydroperoxides. t-Butyl hydroperoxide proved to be a weak oxidant and failed to oxidise alpha-tocopherol in 3 h at 60 degrees C. Inclusion of a small amount of ethanol in the reaction mixture brought about immediate oxidation and the formation of a new product, 5-ethoxymethyl-7,8-dimethyltocol in addition to the spiro dimer and spiro trimer of alpha-tocopherol, alpha-tocopherylquinone and 5-formyl-7,8-dimethyltocol. Formation of 5-ethoxymethyl-7,8-dimethyltocol increased with increasing concentrations of ethanol, up to a maximum of 59% at 20% ethanol. Further increase in ethanol concentration brought about a decrease in the oxidation of alpha-tocopherol and in the formation of 5-ethoxymethyl-7,8-dimethyltocol. Oxidation of the tocopherol model compound 2,2,5,7,8-pentamethyl-6-hydroxychroman under similar conditions produced the analogous product, 5-ethoxymethyl-2,2,7,8-tetramethyl-6-hydroxychroman together with 5-formyl-2,2,7,8-tetramethyl-6-hydroxychroman and 2-(3'-hydroxy-3'-methylbutyl)-3,5,6-trimethylbenzo-1,4-quinone.     

Dynamics of Competition in Populations of Carrot (Daucus carota)

Populations of carrot (Daucus carota) were raised over a widerange of densities (79–5763 plants m^-2) to examine thedynamics of competition in terms of yield–density relationshipsand size variability, and to investigate the effects of nutrientsupply on competition. While the relationship between shootyield and density was asymptotic, the relationship between rootand total yield and density tended to be parabolic. For a giventime and density series the relationship between yield per unitarea and density could best be described by the model: y=w_mD_(1+aD)^b wherey is the yield per unit area,D is density,w_m, a andb arefitted parameters. The parametersw_m anda increased over timebut nutrient availability affected onlyw_m. An extension of thebasic yield-density model is proposed to describe the dynamicsof the yield–density relationship over time: y=kD_{[1+cexp(-rt)]{1+}     

Functional Relevance of Improbable Antibody Mutations for HIV Broadly Neutralizing Antibody Development

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Phylogenetic relationships of the Raphidophyceae and Xanthophyceae as inferred from nucleotide sequences of the 18S ribosomal RNA gene

Some earlier studies suggested an evolutionary relationship between the Raphidophyceae (chloromonads) and Xanthophyceae (yellow-green algae), whereas other studies suggested relationships with different algal classes or the öomycete fungi. To evaluate the relationships, we determined the complete nucleotide sequences of the 18S ribosomal RNA gene from the raphidophytes Vacuolaria virescens, Chattonella subsalsa, and Heterosigma carterae, and the xanthophytes Vaucheria bursata, Botrydium stoloniferum, Botrydiopsis intercedens, and Xanthonema debile. The results showed that the Xanthophyceae were most closely related to the Phaeophyceae. A cladistic analysis of combined data sets (nucleotide sequences, ultrastructure, and pigments) suggested the Raphidophyceae are the sister taxon to the Phaeophyceae-Xanthophyceae clade, but the bootstrap value was low (40%). The raphidophyte genera were united with high (100%) bootstrap values, supporting a hypothesis based upon ultrastructural features that marine and freshwater raphidophytes form a monophyletic group. We examined the relationship between Vaucheria, a siphoneous xanthophyte alga, and the öomycetes, and we confirmed that Vaucheria is a member of the class Xanthophyceae. Partial nucleotide sequences of the 18S rRNA gene from eight xanthophytes (including Bumillariopsis filiformis, Heterococcus caespitiosus, and Mischococcus sphaerocephalus) produce a phylogeny that is not congruent with the current morphology-based classification scheme.