The expansins comprise a family of proteins that appear to be involved in the disruption of the noncovalent bonds between cellulose microfibrils and cross-linking glycans, thereby promoting wall creep. To understand better the expansion process in Petunia hybrida (petunia) flowers, we isolated a cDNA corresponding to the PhEXP1 a-expansin gene of P. hybrida. Evaluation of the tissue specificity and temporal expression pattern demonstrated that PhEXP1 is preferentially expressed in petal limbs during development. To determine the function of PhEXP1, we used a transgenic antisense approach, which was found to cause a decrease in petal limb size, a reduction in the epidermal cell area, and alterations in cell wall morphology and composition. The diminished cell wall thickness accompanied by a reduction in crystalline cellulose indicates that the activity of PhEXP1 is associated with cellulose metabolism. Our results suggest that expansins play a role in the assembly of the cell wall by affecting either cellulose synthesis or deposition.

Two chemically mutagenized agerminative variants of Candida albicans were used to immunize mice against challenge with highly virulent cells of the parent strain. Although both mutants (Vir-3 and Vir-13) resulted in nonlethal infection and could be recovered from mouse organs for many days after the intravenous inoculation of 10' to 106 cells, significant protection to systemic challenge with virulent C. albicans was induced by only one (Vir-3) of the two variants. Anticandidal resistance in Vir-3-infected mice was associated with the occurrence in vivo of strong delayed-type hypersensitivity to Candida antigen, detection in vitro of highly fungicidal effector macrophages, and presence in the serum of a large proportion of Candida-reactive antibodies of the immunoglobulin G2a isotype. Bulk cultures of purified CD4+ lymphocytes from mice infected with either mutant were compared for their ability to produce gamma interferon (IFN-y), interleukin-2 (IL-2), IL-4, and IL-6 in vitro. After stimulation with specific antigen, CD4+ cells from Vir-3-immunized mice released large amounts of the Thl-specific cytokines, IFN-'y and IL-2, at a time when CD4+ cells from Vir-13-infected mice predominantly secreted the characteristic Th2 cytokines, IL-4 and IL-6. These results were confirmed by quantitative analysis of cytokine-producing Thl and Th2 cells. In addition, only mice infected with Vir-3 displayed a high frequency of CD8+ cells with the potential for in vitro lysis of yeast-primed bone marrow macrophages. Purified CD4+ cells from Vir-3-infected mice, but not a mixture of these cells with CD4+ lymphocytes from mice infected with Vir-13, could adoptively transfer delayed-type hypersensitivity reactivity onto naive mice. Taken together, these data suggest that both Thl and Th2 CD4+ lymphocytes may be activated during experimental C. albicans infection in mice.

The definition of the patterns of cell division and expansion in plant development is of fundamental importance in understanding the mechanics of morphogenesis. By studying cell division and expansion patterns, we have assembled a developmental map of Petunia hybrida petals. Cycling cells were labelled with in situ markers of the cell cycle, whereas cell expansion was followed by assessing cell size in representative regions of developing petals. The outlined cell division and expansion patterns were related to organ asymmetry. Initially, cell divisions are uniformly distributed throughout the petal and decline gradually, starting from the basal part, to form a striking gradient of acropetal polarity. Cell areas, in contrast, increased first in the basal portion and then gradually towards the petal tip. This growth strategy highlighted a cell size control model based on cell-cycle departure time. The dorso-ventral asymmetry can be explained in terms of differential regulation of cell expansion. Cells of the abaxial epidermis enlarged earlier to a higher final extent than those of the adaxial epidermis. Epidermal appendage differentiation contributed to the remaining asymmetry. On the whole our study provides a sound basis for mutant analyses and to investigate the impact of specific (environmental) factors on petal growth.

We address the taxonomic position of the southern European individuals of pike, performing a series of tests and comparisons from morphology, DNA taxonomy and population genetics parameters, in order to support the hypothesis that two species of pike, and not only one, exist in Europe. A strong relationship emerged between a northern genotype supported by COI, Cytb, AFLP and specific fragments, and a phenotype with round spot skin colour pattern and a large number of scales in the lateral line, clearly separated from a southern genotype with other skin colour pattern and a low number of scales in the lateral line. DNA taxonomy, based on a coalescent approach (GMYC) from phylogenetic reconstructions on COI and Cytb together with AFLP admixture analysis, supported the existence of two independently evolving entities. Such differences are not simply due to geographic distances, as northern European samples are more similar to Canadian and Chinese samples than the southern Europe ones. Thus, given that the differences between the two groups of European pike are significant at the phenotypic, genotypic and geographical levels, we propose the identification of two pike species: the already known northern pike (Esox lucius) and the southern pike (E. flaviae n.sp.). The correct identification of these two lineages as independent species should give rise to a ban on the introduction of northern pikes in southern Europe for recreational fishing, due to potential problems of hybridisation.

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