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Leaf venation patterns vary considerably between species and between leaves within a species. A mechanism based on canalization of auxin transport has been suggested as the means by which plastic yet organized venation patterns are generated. This study assessed the plasticity of Arabidopsis thaliana leaf venation in response to ectopic ground or procambial cell divisions and auxin transport inhibition (ATI). Ectopic ground cell divisions resulted in vascular fragments between major veins, whereas ectopic procambial cell divisions resulted in additional, abnormal vessels along major veins, with more severely perturbed lines forming incomplete secondary and higher-order venation. These responses imply limited vascular plasticity in response to unscheduled cell divisions. Surprisingly, a combination of ectopic ground cell divisions and ATI resulted in massive vascular overgrowth. It is hypothesized that the vascular overproduction in auxin transport-inhibited wild-type leaves is limited by simultaneous differentiation of ground cells into mesophyll cells. Ectopic ground cell divisions may negate this effect by providing undifferentiated ground cells that respond to accumulated auxin by differentiation into vascular cells.

Background and Aims: The root meristem of the Arabidopsis thaliana mature embryo is a highly organized structure in which individual cell shape and size must be regulated in co-ordination with the surrounding cells. The objective of this study was to determine the role of the AUX1 LAX family of auxin import carriers during the establishment of the embryonic root cell pattern., Methods: The radicle apex of single and multiple aux1 lax mutant mature embryos was used to evaluate the effect of this gene family upon embryonic root organization and root cap size, cell number and cell size., Key Results: It was demonstrated here that mutations within the AUX1 LAX family are associated with changes in cell pattern establishment in the embryonic quiescent centre and columella. aux1 lax mutants have a larger radicle root cap than the wild type and this is associated with a significant increase in the root-cap cell number, average cell size, or both. Extreme disorganization of the radicle apex was observed among quadruple aux1 lax1 lax2 lax3 mutant embryos, but not in single aux1 null or in lax1, lax2 and lax3 single mutants, indicating redundancy within the AUX1 LAX family., Conclusions: It was determined that the AUX1 LAX family of auxin influx facilitators participates in the establishment of cell pattern within the apex of the embryonic root in a gene-redundant fashion. It was demonstrated that aux1 lax mutants are affected in cell proliferation and cell growth within the radicle tip. Thus AUX1 LAX auxin importers emerge as new players in morphogenetic processes involved in patterning during embryonic root formation.

A new method is described for fluorescent imaging of mature Arabidopsis embryos that enables their cellular architecture to be visualized without the need for histological sectioning. Mature embryos are stained with aniline blue and cleared with chloral hydrate to allow high-resolution confocal imaging of individual cells within the embryo prior to germination. The technique allows the collection of longitudinal optical sections throughout the cotyledon, hypocotyl and root of wild-type Arabidopsis C24 embryos. Every cell within the mature embryo can be visualized with sufficient clarity and resolution to allow three-dimensional analysis of cellular architecture. Optical sectioning of mutant gnom, short-root and scarecrow embryos, and through root meristems disrupted as a consequence of targeted misexpression of diphtheria toxin, demonstrate the potential of this technique for visualizing the cellular organization of mutant and perturbed embryonic phenotypes.

Mutation of the COMATOSE locus in Arabidopsis results in a marked reduction in germination potential. Whilst the morphology of comatose (cts) embryos is not altered, physiological analysis reveals that mature cts seeds do not respond to gibberellin. Prolonged chilling of imbibed seeds only partially restores germination potential, and seeds do not after ripen. Genetic analysis shows that the cts phenotype is expressed in the embryo and phenotypic differences between wild-type and mutant plants were not observed during other stages of plant growth and development. Therefore cts represents a new class of mutant, with a specific lesion that results in severely impaired germination potential. Genetic interactions were analysed between cts and loci that regulate embryo maturation, and abscisic acid biosynthesis and perception. Results from these studies showed that the cts mutant phenotype required the wild-type action of these loci, and suggested that CTS exerts a repressive function on these loci. A model is presented postulating that CTS promotes increased germination potential, and represses embryo dormancy. These functions of CTS may result in the removal of embryo dormancy as a prerequisite to germination.

AFLP (amplified fragment length polymorphism) fingerprinting of cultivars of bread wheat (Triticum aestivum) and some of its wild relatives has allowed the efficient detection of large numbers of polymorphic amplified fragments. While the reproducibility of fingerprints in repeated experiments is high, pattern differences were observed between fingerprints obtained from seed and leaf DNA template from the same wheat accession. These distinct organ specific amplified DNA fragments were shown to be due neither to genotypic mixtures nor to pathogen contamination. They are likely a result of differences in DNA methylation between organs. Even greater numbers of organ specific amplified fragments were observed when fingerprints obtained from the root and shoot of individual seedlings of the wheat relatives Aegilops mutica and Aegilops speltoides were compared. This phenomenon underlines the importance of ensuring that DNA is extracted from physiologically uniform tissue in phylogenetic studies based on AFLP fingerprints. For this purpose, mature seed is a convenient source.

The inheritance of B chromosomes has been investigated. In Allium schoenoprasum from the River Wye, Powys; controlled crosses between plants of known B chromosome constitution were carried out, and the numbers of Bs present in the progenies scored. There was considerable heterogeneity in B chromosome transmission rates across the range of B chromosome numbers, through both the male and female lines, and in crosses involving odd and even numbers of Bs. The mean B number of the progeny was lower than the Mendelian expectation in 41 of the 57 crosses, significantly so in about a third of cases. No progeny had a mean B number significantly higher than expected. The mean transmission rate per B was not significantly different between parents with different numbers of Bs, in either the male or female line, or between plants carrying odd or even numbers of Bs. Transmission through the male line (0.43) was higher than through the female line (0.35), but not significantly so. The overall mean transmission rate per B (0.4), estimated from all crosses, was significantly lower than the expected rate of 0.5. This study provides conclusive evidence that B chromosomes in A. schoenoprasum from the River Wye lack an effective accumulation mechanism and, furthermore, show significant losses during transmission to the progeny of controlled crosses.

The preparation and properties of the copper(II) complex Cu(SUP)2.H2O are reported for the anti-inflammatory drug Suprofen (SUP). The diffuse reflectance spectra and magnetic moment are consistent with a dinuclear structure as found for [Cu(aspirinate)2(H2O)]2. The copper(II) complex exhibits an increased superoxide dismutase activity compared with the parent drug molecule in the nitroblue tetrazolium assay.