Radiana Cozza

Influence of growth medium on mineral composition and leaf histology in micropropagated plantlets of Olea europaea

The effects of the medium on the nutritional status and leaf histology of micropropagated shoots have been investigated in two different cultivars of Olea europaea L. The results showed that different media, as well as intraspecific variations between cultivars, strongly influences the mineral composition of the shoots. Furthermore the level of tissue differentiation in vitro was dependent on the medium and appeared to be related to the capacity of plantlets to survive the acclimatation phase.

Amount and organization of the heterochromatin in Olea europaea and related species

The amount and spatial organization of the heterochromatin in nuclei of the shoot meristem and the frequency in the nuclear DNA of sequences belonging to a family of tandem repeats were investigated in cultivars of Olea europaea and related species. Significant differences between Olea species and between cultivars of O. europaea were observed: (i) in the spatial organization of the heterochromatin in interphase nuclei as determined by the number and surface area of the chromocentres; (ii) in genome size; and (iii) in the amount of condensed chromatin as measured by cytophotometry carried out at different thresholds of optical density. DNA elements belonging to a family of tandem repeats about 80 bp in length (OeTaq80 repeats) were isolated from the genomic DNA of an olive cultivar. It was shown: (i) by nucleotide sequence comparisons, that these repeats display variability in structure even within the same array, where different elements may share no more than 74% homology; (ii) by in situ hybridization, that OeTaq80-related DNA sequences are mainly localized in the heterochromatin at the chromosome ends; (iii) by dot-blot hybridization experiments, that these sequences are highly represented in the genome of all the olive cultivars and the majority of Olea species studied, and that their frequency may differ significantly even between olive cultivars; and (iv) by calculating the copy number of OeTaq80-related sequences per haploid (1C) genome, that the redundancy of these DNA elements may differ significantly between the genomes tested. It is suggested that the inter- and intraspecific changes in the nuclear and genomic traits observed can contribute to the understanding of the phylogenetic relationships between Olea species and in defining parameters to be exploited in varietal identification within cultivated olives.

Molecular cloning, characterisation and expression of two catalase genes from peach

Two cDNA clones encoding catalase (Cat1 and Cat2) from peach [Prunus persica (L.) Batsch] were identified, that show homologies to other plant catalases. The nucleotide sequences of the two coding regions showed 88% identity to each other. The amino acid sequences predicted from the two full-length clones showed the highest homology to a catalase from cotton and Nicotiana plumbaginifolia L. and included C-terminal tri-peptides typical of those used to target proteins to peroxisomes. Southern hybridisation analysis suggested the existence of two catalase genes in peach. The expression of Cat1 and Cat2 was determined in seeds, vegetative tissue, leaves during the seasonal cycle and in leaves in response to light / dark treatments. Cat1 had high levels of expression only in leaf tissue and was responsive to light and seasonal changes. Cat2 had high levels of expression in in vitro shoots and was also responsive to seasonal changes, but not to light. In situ hybridisations to leaf tissue indicated that the expression of Cat1 was localised mainly in palisade cells, while Cat2 mRNA was present in the vascular tissue. The results of the expression analysis and in situ hybridisation suggest a role for Cat1 in photorespiration and for Cat2 in stress responses.

Expression pattern of a type-2 metallothionein gene in a wild population of the psammophyte Silene nicaeensis

Silene nicaeensis is a wild Mediterranean grass often restricted to sandy sea shore and exhibiting an excellent tolerance to drought and salinity. Within Silene genus, several heavy metal-tolerant ecotypes have been identified, but information on molecular basis of such metal tolerance is still limited. Conceivably, salt-tolerant plants may represent a powerful tool for the remediation of heavy metal contaminated sites in saline environment. Here, a gene encoding a metallothionein protein was isolated from S. nicaeensis. Sequence analysis identified the motifs characteristic of type II metallothionein and designated as SnMT2. SnMT2 expression was investigated in plants collected from two sites differing in Metal Pollution Index (MPI). SnMT2 expression by polymerase chain reaction-based semi-quantitative transcript analysis showed a high accumulation in the leaves; in situ hybridization showed a steady localization of SnMT2 mRNA in the vascular bundle and in proliferating tissues. Moreover, an increase of SnMT2 was observed in the root of plants collected from area with higher MPI. The putative role of SnMT2 in metal tolerance is discussed.

Note: Molecular identification of ‘Candidatus phytoplasma asteris’ inducing histological anomalies inSilene nicaeensis

Numerous plants ofSilene nicaeensis having symptoms resembling those associated with the presence of phytoplasmas were observed in an extensive coastal area in the south of Italy. Microscopic observation showed histological abnormalities in the organization of tissues in symptomatic plants, and molecular tests, including PCR/RFLP analyses and nucleic acid sequencing, revealed the presence of phytoplasmas belonging to the aster yellows group (‘Candidatus phytoplasma asteris’). This is the first report of phytoplasma infection inS. nicaeensis, a wild species that colonizes the Calabrian coast.

Ultrastructural features, chromium content and in situ immunodetection of 5-methyl-cytosine following Cr (VI) treatment in two strains of Scenedesmus acutus M. (Chlorophyceae) with different chromium sensitivity

Abstract Two strains of the unicellular green alga Scenedesmus acutus (F.J.F. Meyen) with different sensitivity to chromium (VI) were compared to evaluate their ultrastructural morphology in chromium-free and -supplemented medium with a sub-lethal concentration of Cr(VI) for 72 hours. The ultrastructural alteration in different cytological compartments indicated that Cr(VI) induced earlier and stronger alterations in the wild type (wt) compared with the chromium-tolerant strain (Cr-t). After Cr treatments, ICP-MS (Inductively Coupled Plasma Mass Spectrometry) showed a higher Cr accumulation in the wild type than in the Cr-tolerant strain, suggesting a more efficient chromium-exclusion mechanism in the latter. The Cr treatment induced an increase in the nuclear area and a rearrangement in the eu-heterochromatic fraction, suggesting that chromatin remodelling could be at the basis of differential gene expression and metal tolerance. To gain additional information on the remodelling of the nuclear chromatin, we analysed DNA methylation by immunolocalization of 5-methyl-cytosine, before and after Cr exposure. Significant differences in the quantification of the immunolabelling of DNA cytosine-rich zones between the two strains were observed. These data suggest that an epigenetic mechanism could be at the basis of the Cr tolerance in S. acutus, as supported by previous data reporting that the acquired tolerance was inherited and maintained through the progeny.