Francesca Dalla Vecchia

Changes in onion root development induced by the inhibition of peptidyl-prolyl hydroxylase and influence of the ascorbate system on cell division and elongation

Abstract. Post-translational hydroxylation of peptide-bound proline residues, catalyzed by peptidyl-prolyl-4 hydroxylase (EC 1.14.11.2) using ascorbate as co-substrate, is a key event in the maturation of a number of cell wall-associated hydroxyproline-rich glycoproteins (HRGPs), including extensins and arabinogalactan-proteins, which are involved in the processes of wall stiffening, signalling and cell proliferation. Allium cepa L. roots treated with 3,4-DL-dehydroproline (DP), a specific inhibitor of peptidyl-prolyl hydroxylase, showed a 56% decrease in the hydroxyproline content of HRGP. Administration of DP strongly affected the organization of specialized zones of root development, with a marked reduction of the post-mitotic isodiametric growth zone, early extension of cells leaving the meristematic zone and a huge increase in cell size. Electron-microscopy analysis showed dramatic alterations both to the organization of newly formed cell walls and to the adhesion of the plasma membranes to the cell walls. Moreover, DP administration inhibited cell cycle progression. Root tips grown in the presence of DP also showed an increase both in ascorbate content (+53%) and ascorbate-specific peroxidase activity in the cytosol (+72%), and a decrease in extracellular “secretory” peroxidase activity (−73%). The possible interaction between HRGPs and the ascorbate system in the regulation of both cell division and extension is discussed.

Some effects of cadmium on maize plants

The growth of the whole plant and the chlorophyll content, oxygen evolution, and chloroplast ultrastructure of leaf tissues have been studied in maize plants grown on a culture medium either without cadmium (Cd) or supplied with increasing concentrations of the metal. The plants treated with high Cd concentrations showed symptoms of heavy metal toxicity, such as length reduction of both roots and shoots, leaf bleaching, ultrastructural alterations of chloroplasts and lowering of photosynthetic activity. Some symptoms appeared at 100 μM Cd, but the strong toxic effects of the metal were found only at 250 μM Cd.

Involvement of p53 in specific anti-neuroectodermal tumor activity of aloe-emodin

Previously, we have identified aloe‐emodin (AE) as a new type of anticancer agent, with activity that is based on apoptotic cell death promoted by a neuroectodermal tumor‐specific drug uptake. We attempt to clarify the intracellular target of AE and the apoptosis‐signaling pathway activated by AE in neuroblastoma cell lines. Two‐photon excitation microscopy and spectroscopic titrations documented that AE is highly concentrated in susceptible cells and binds to DNA. One of the most important mediators of apoptotic response to genotoxic stimuli, such as anticancer agents, is the p53 tumor suppressor gene. To evaluate the role played by p53 in AE‐induced apoptosis a p53 mutant cell line, which lacks transcriptional activity of p53 targeted genes, was tested. AE displayed a reduced growth inhibitory and pro‐apoptotic activity in p53 mutant cells (SK‐N‐BE(2c)) with respect to the p53 wild‐type line (SJ‐N‐KP). This effect was not caused by a reduced drug uptake in the mutant neuroblastoma cell line but was related to a different apoptotic cell phenotype. Whereas SJ‐N‐KP cells were susceptible to a p53 transcription‐dependent pathway of apoptosis, SK‐N‐BE(2c) cells underwent apoptosis with up‐regulation of p53 expression but not of p53‐target genes. After AE treatment p53 translocates to the mitochondria inter‐membrane space in both neuroblastoma cell lines. Due to its high accumulation in neuroectodermal tumor cells AE could also kill tumor cells harboring p53 mutant genes. This property would further contribute to AE specific anti‐tumor activity and might be exploitable in the clinic.

Morphological and ultrastructural aspects of dehydration and rehydration in leaves of Sporobolus stapfianus

The resurrection species Sporobolus stapfianus Gandoger has been studied by LM, TEM and SEM in order to define the leaf morphology and fine structure and to analyse the cellular changes occurring during the processes of dehydration and rehydration of the plant. Some characteristics of the fully hydrated leaf and some ultrastructural and physiological events which take place during leaf wilting are discussed in relation to their possible role in plant desiccation-tolerance.The leaves of S. stapfianus show several characteristics common among xerophytic species. In the resurrection leaf they could play a role in slowing down the drying rate, thus leaving time to activate the mechanisms protecting the cell structures against drought damage. Actually, the S. stapfianus leaves do not undergo important cellular alterations during dehydration. The chloroplasts, in particular, retain part of their photosynthetic pigments and thylakoid membranes. Upon rewatering leaf recovery is rather fast and the tissue structure and cell organization of the fully hydrated state are already regained after two days.

Accumulation of selenium in Ulva sp. and effects on morphology, ultrastructure and antioxidant enzymes and metabolites

The impact of selenium (Se) on Ulva sp., a green macroalga naturally growing in the Venice Lagoon, was investigated. The alga was provided for 10 days with concentrations of selenate (Na(2)SeO(4)) ranging from 0 to 100 μM. Se accumulation in the algal biomass was linearly related to the selenate dose and this relationship was not affected by the high sulfate concentration measured in the seawater. The amount of Se measured in the alga was always relatively low and not hazardous to algal consumers. However, Se induced the formation of hydrogen peroxide (H(2)O(2)) in Ulva sp. and, as a result, the activity of antioxidant enzymes (superoxide dismutase, SOD, and catalase, CAT) and the amount of antioxidant metabolites (phenols, flavonoids and carotenoids) increased, even when selenate was supplied to the macroalga at low concentration (2.5 μM). This indicated that different components of the antioxidant defence system played a pivotal role in overcoming oxidative damage by Se in the macroalga, and explained the lack of morphological and ultrastructural alterations in Ulva sp. exposed to selenate.

Amitrole Effects on Chloroplasts of Barley Plants Grown at Different Temperatures

Summary The effects of amitrole, a bleaching herbicide affecting carotenogenesis, were studied in barley plants grown in light at 20 °C and at 30 °C. At the lower temperature the herbicide caused dramatic damage to the leaf chloroplasts, compared with control plants. The synthesis of protective carotenoids was drastically impaired, with some accumulation of lycopene and a very low production of β-carotene and xanthophylls. In chloroplasts this effect of amitrole was related to a fall in chlorophyll content, reduction of the thylakoid system and destruction of most 70S ribosomes. Though the damaged organelles maintained a certain ability to synthesize proteins, chlorophyll-binding polypeptides encoded by plastid DNA were not found in the altered thylakoids which, however, contained chlorophyll-binding proteins and other polypeptides encoded by the nuclear DNA. Amitrole appeared to be less effective in plants grown at 30 °C. The synthesis of the protective carotenoids was greatly increased and the chloroplasts exhibited structure and composition almost similar to those of control organelles. The possible existence in the carotenoid biosynthetic pathway of alternative thermo-modulated steps, with different amitrole sensitivity, is suggested.

Ultrastructural and Photosynthetic Features of Leaves and Stems of Elodea canadensis

Summary Leaves and stems of Elodea canadensis Michx have been characterized morphologically and ultrastructurally. Significant features, such as chloroplast structure and distribution in the different tissues, the transfer cell-like organization of the lower leaf cells, the gas-lacunae of the stem cortical region and the hydrophobic material present in the cell walls, have been described and specially considered in relation to their possible role in fulfilling the photosynthetic demands of the two organs. In order to verify the possibility that the two green organs may adopt different strategies to supply themselves with inorganic C, the ability of leaves and stems to carry out photosynthesis in different environmental conditions, such as different water pH and dissolved inorganic carbon (DIC) availability, has also been studied in this submerged plant. The results show that the leaves in Elodea canadensis are the -truly submerged. organs, well adapted to underwater life. They have ultrastructural features corresponding to an enhancement of the water-cell exchanges and can utilize with high efficiency both the environmental CO2 and HCO-3 as inorganic C sources. The stem, on the contrary, behaves as a «terrestrial organ, whose photosynthetic ability strictly depends on the availability of CO2 entrapped in the wide intercellular spaces of its tissues.

Ecological, physiological, and biomolecular surveys on microalgae from Ross Sea (Antarctica)

Abstract Results of analyses on pico, nano‐ and microphytoplankton from the sea‐ice of Terra Nova Bay, during austral summer 1995–96, are reported. In this environment, among the 116 taxa that we found, the most abundant were diatoms (102). The interior algal community of the sea‐ice was dominated by Fragilariopsis spp., Archeomonas areolata, and hypnozygotes of Porella glacialis. In the algal mat at the deeper layer of the ice, however, diatoms showed higher density. Photoautotrophic picoplankton was also present and red‐fluorescing cells, small eukaryotes and phycocyanin‐rich cyanobacteria prevailed over phycoerythrin‐rich cyanobacteria. Besides these data, ultrastructural, physiological and biomolecular surveys on three Antarctic sea water microalgae, of which only Koliella antarctica was known, were also carried out. The 18S rDNA gene sequences of K. antarctica and other closely related species allowed us to verify that the Koliella genus belongs to Trebouxiophyceae, while as regards the other two taxa, one of them was found to belong to the Heterococcus and the other to the Pyramimonas genus. They might be unde‐scribed species of the Southern Ocean. Pyramimonas sp., found in Terra Nova Bay during the austral summer 1998–99, carried tri‐chocysts. Moreover, K. antartica, like Heterococcus sp., showed great ability to live both in fresh water and at different salinities.

Somatic embryogenesis and indole alkaloid production in Catharanthus roseus

ABSTRACT A new protocol to obtain an embryogenic cell line from cultured seedling explants of Catharanthus roseus is described. In order to assess the relationship between tissue differentiation and secondary metabolite biosynthesis, the biosynthetic capabilities (alkaloid production) of an embryogenic cell line and two non-embryogenic C. roseus strains were comparatively examined. Faster cell growth rate was associated with higher alkaloid production in the embryogenic cell line. The kinetics of ajmalicine and serpentine production by the three cell lines is also reported.

Effects of seed chilling or GA3 supply on dormancy breaking and plantlet growth in Cercis siliquastrum L.

Germination and post-germination events have been compared in seeds of Cercis siliquastrum whose dormancy was removed by fulfilling the natural chilling requirement or by exogenous GA3 application.Compared to the chilled ones, the GA3 treated seeds showed precocious embryo growth and an earlier reserve mobilization, which started before radicle emergence.Although the hormonal application was interrupted at seed germination, the plantlets of Cercis siliquastrum that originated from GA3-supplied seeds were taller than those from chilled ones. Moreover, they produced a greater number of leaves but a reduced root mass and had some difficulty in maintaining a good water balance.Thus, the treatment of Cercis siliquastrum seeds with exogenous GA3 broke dormancy and induced germination, but also caused long-lasting consequences on morphogenesis of the growing plantlet.