The role of mineral ions in controlling morphogenesis in plants: a case of the inhibition of growth of the hypocotyle of Bidens pilosa L

Mineral ions are implicated in various events occurring in the transduction of messages in plants, from the reception of the initial signal to the final morphogenetic expression. Ions may be involved also in the possible migration, storage and retrieval of the message. In a number of cases, cellular exchange of Ca2+ have been shown to occur at the reception of a signal. This is the reason why Ca2+ has often been considered as a "second messenger". For the possible message migration, cellular exchanger of Cl-, K+, H+ and Ca2+ are involved in the propagation of a wave of electric depolarization. The mechanisms underlying the possible storage of the message in a plant are still not clearly understood. However, ions such as K+, Na+ and Ca2+ interfere with the retrieval of the stored information. There are some indications that protons are involved in the metabolic reactions responsible for the final morphogenetic expression of the original signal. Moreover, the addition of Li+ ions inhibits, or shifts the latter effects, while the action of Li+ is counterbalanced by increasing the concentration of K+. The particular case of the inhibition of the growth of Bidens hypocotyles following delivering a few needle pricks to the cotyledons has been examined in more details.     

Phylogeny of Greya (Lepidoptera: Prodoxidae), based on nucleotide sequence variation in mitochondrial cytochrome oxidase I and II: congruence with morphological data

The phylogeny of Greya Busck (Lepidoptera: Prodoxidae) was inferred from nucleotide sequence variation across a 765-bp region in the cytochrome oxidase I and II genes of the mitochondrial genome. Most parsimonious relationships of 25 haplotypes from 16 Greya species and two outgroup genera (Tetragma and Prodoxus) showed substantial congruence with the species relationships indicated by morphological variation. Differences between mitochondrial and morphological trees were found primarily in the positions of two species, G. variabilis and G. pectinifera, and in the branching order of the three major species groups in the genus. Conflicts between the data sets were examined by comparing levels of homoplasy in characters supporting alternative hypotheses. The phylogeny of Greya species suggests that host-plant association at the family level and larval feeding mode are conservative characters. Transition/transversion ratios estimated by reconstruction of nucleotide substitutions on the phylogeny had a range of 2.0-9.3, when different subsets of the phylogeny were used. The decline of this ratio with the increase in maximum sequence divergence among taxa indicates that transitions are masked by transversions along deeper internodes or long branches of the phylogeny. Among transitions, substitutions of A-->G and T-->C outnumbered their reciprocal substitutions by 2-6 times, presumably because of the approximately 4:1 (77%) A+T-bias in nucleotide base composition. Of all transversions, 73%-80% were A<-->T substitutions, 85% of which occurred at third positions of codons; these estimates did not decrease with an increase in maximum sequence divergence of taxa included in the analysis. The high frequency of A<-->T substitutions is either a reflection or an explanation of the 92% A+T bias at third codon positions.