Franca Tommasi

Effect of some light rare earth elements on seed germination, seedling growth and antioxidant metabolism in Triticum durum

Rare earth elements (REEs) enriched fertilizers have been commonly used in China since the 1980s, thus inducing a growing concern about their environmental impact in agriculture. In this work, the effect of some light REEs nitrate mixture and La(3+) nitrate on seed germination, seedling growth and antioxidant metabolism in Triticum durum was investigated with the aim of clarifying the potential benefits or damages of REEs on plants. Seed pre-soaking for 8 h with La(3+) and REEs nitrate inhibited seed germination at low concentrations (0.01 mM and 0.1 mM), while pre-soaking for 2 and 4 h already inhibited seed germination when higher concentrations (1 mM and 10 mM) of La(3+) and REEs nitrate were used. La(3+) and REEs nitrate treatment also affected seedling growth. Root growth was enhanced and inhibited at low and high concentrations, respectively. Shoot growth was inhibited by La(3+) and REEs nitrate at all tested concentrations after 12 d of treatments. Enzymatic and non enzymatic antioxidants were differently affected by La(3+) and REEs nitrate and their behaviour changed also depending on the plant organ. In roots La(3+) and REEs nitrate treatments induced an increase in ascorbate (ASC) and glutathione (GSH) contents. In shoots only La(3+) nitrate induced an increase in the ASC content whereas GSH decreased following both La(3+) and REEs nitrate treatments. An increase in ASC peroxidase activity was observed in shoots and roots, while catalase did not change in roots and slightly decreased in shoots. The possible role of the increase in some antioxidants as indicators of stress caused by lanthanide treatments is discussed.

Ascorbic acid utilization by prolyl hydroxylase in vivo

Abstract The treatment with 3,4-dehydro- d , l -proline, an analogous compound of proline which specifically inhibits prolyl hydroxylase, reduces the quantity of the hydroxyproline residues present in the polypeptide chains and at the same time leads to an increase in the ascorbic acid content in different plant tissues analysed (pea embryos, carrot and potato slices). The increase of ascorbic acid induced by dehydroproline treatment can be interpreted as a consequence ofthe reduced activity of the prolyl hydroxylase and suggests that in vivo the ascorbic acid acts as electron donor in the process of proline hydroxylation.

In vivo inhibition of galactono-γ-lactone conversion to ascorbate by lycorine

Summary Maize embryos are endowed with the ascorbate biosynthetic system and the last enzyme of the pathway, galactono oxidase (or dehydrogenase), is very active; L-galactono-γ-lactone addition gives rise to a 3-fold increase in cellular ascorbate content. Lycorine, an alkaloid extracted from members of the Amaryllidaceae, strongly inhibits the in vivo conversion of L-galactono-γ-lactone to ascorbic acid. Data reported here seem to suggest that lycorine forms a relatively stable association with galactono oxidase; incubation with 50 μM lycorine shows a marked inhibitory effect that persists when the alkaloid is removed from the incubation medium. The inhibitory effect of lycorine is significantly higher in onion roots and pea embryos in comparison with maize embryos. This different sensitivity to the alkaloid can be explained by the inability of onion and pea to overcome the decrease in ascorbate biosynthesis by means of dehydroascorbate reductase, which has a significantly lower activity in these two species than that in maize embryos. Galactono oxidase also efficiently utilizes L-gulono-γ-lactone, the physiological substrate of the animal enzyme. Considering that lycorine induces scurvy-like symptoms in ascorbic acid-synthesizing animals, it is reasonable to suppose that lycorine inhibits ascorbate biosynthesis in both plants and animals by acting on the last step in the biosynthetic pathway leading from sugar to ascorbate.

Ascorbic acid requirement for increased peroxidase activity during potato tuber slice aging

The increase in peroxidase activity during aging is a well known process depending on de novo enzyme synthesis. The enhancement of peroxidase is strongly inhibited by lycorine, an ascorbic acid biosynthesis inhibitor. The inhibitory effect of lycorine can be abolished by experimentally increasing the ascorbic acid concentration in the tissues. Conversely, glucose‐6‐phosphate dehydrogenase enhancement ‐ which also occurs during the aging of potato slices ‐ depends on protein synthesis but does not require ascorbic acid. It is suggested that the role of ascorbic acid in the development of peroxidase activity may be related to controlling the synthesis of hydroxyproline‐containing proteins. A possible relationship between peroxidase increase and hydroxyproline‐containing proteins biosynthesis is discussed.

Responses of antioxidant systems to lanthanum nitrate treatments in tomato plants during drought stress

Abstract Lanthanum is one of the most abundant elements in rare earths enriched fertilizers and is supposed to be one of the main responsible of the effects of such fertilizers on crops. In this work, the effect of lanthanum nitrate on H2O2 production, lipid peroxidation, ascorbate and glutathione content, and on the activity of cytosolic ascorbate peroxidase, dehydroascorbate reductase, monodehydroascorbate reductase, and glutathione reductase in Lycopersicon esculentum L. cv. Marmande during drought stress was evaluated. The results confirmed that treatments of tomato plants with lanthanum nitrate affect the antioxidant cellular defences and that lanthanum toxicity is dependent on the way of treatment. The stimulation of antioxidant systems did not induce any improvement in drought stress responses in tomato but seemed to be only a consequence of the unbalance in cell metabolism due to the treatment with lanthanum nitrate.

Karyomorphological and biochemical studies in Glebionis coronaria (L.) Spach and Glebionis segetum (L.) Fourreau from Italy

Abstract The karyotype structures and the composition and distribution of the heterochromatin in Glebionis coronaria and Glebionis segetum using Giemsa and fluorescent banding techniques were analysed. The species studied are diploids with 2n = 2x = 18 chromosomes. G. coronaria possesses the most symmetrical karyotype, comprising mainly metacentric chromosomes. G. segetum, with formula 12 m + 6 sm, showed a slightly less symmetrical karyotype. Giemsa C‐banding revealed little constitutive heterochromatin in both species. The presence of telomeric bands was restricted to two chromosome pairs. After staining with chromomycin A3, the chromosomes of G. coronaria and G. segetum revealed bright fluorescence at the telomeric regions of two chromosomes. No 4‐6‐diamidino‐2‐phenyl‐indole bright blocks were observed. To estimate genetic variability in the species under consideration, genotypic expression was also determined through isozyme electrophoresis of cytosolic ascorbate peroxidase, considered a genetic marker in the study of plant phylogenetics. The relationships between G. coronaria and G. segetum are discussed. Abbreviations: ASC, ascorbate; BSA, bovine serum albumin; cAPX, cytosolic ascorbate peroxidase; CMA, chromomycin A3; DAPI, 4‐6‐diamidino‐2‐phenyl‐indole; EDTA, ethylenediaminetetraacetic acid; PAGE, polyacrylamide gel electrophoresis

The Ascorbic Acid System in Cuscuta reflexa Roxb.

Summary Seedlings of the parasitic plant Cuscuta reflexa Roxb. synthesize ascorbic acid (AA); however, the conversion of galactono-γ-lactone (GL) to AA is low in respect to other angiosperms. The AA content of the seedlings, as well as the AA/dehydroascorbic acid (DHA) ratio, is much lower than in any other higher plant. Cuscuta has no AA oxidase, but it does have AA peroxidase, its activity being similar to that found in normal green plants. Both the reducing enzymes-ascorbic free radical (AFR) reductase and DHA reductase- are present in this parasitic plant. DHA reductase activity is fairly high; while, that of AFR reductase is ten times lower than in etiolated and green plants. These results suggest that AFR reductase is a key enzyme for maintaining the AA system in the reduced state and explain why the AA/DHA ratio is low in this parasitic plant.

Cytosolic ascorbate peroxidase in Gymnosperms

ABSTRACT Sixteen species of Gymnosperms have been screened for cytosolic ascorbate peroxidase by means of native polyacrylamide gel electrophoresis. This analysis shows that a single form of the enzyme is the most common situation. The enzyme reveals a similar electrophoretic mobility in species belonging to the same genus and sometimes to different genera. In some Pinaceae, two bands of activity were observed. The presence in the archaic spermatophyte Ginkgo biloba, as well as in the more advanced monocotyledons, of three isoforms of ascorbate peroxidase, might suggest that three different cytosolic ascorbate peroxidase genes were already present in this archaic species.

The biogenesis of galactone-γ-lactone oxidase in Avena sativa embryos

Abstract In Avena sativa embryos, the biogenesis of galactono-γ-lactone oxidase, the enzyme which catalyses the last step of the ascorbic acid biosynthetic pathway is inhibited by both mitochondrial and cytoplasmic protein synthesis inhibitors. In the same experimental conditions (incubating embryos with protein synthesis inhibitors) glucose-6-phosphate dehydrogenase biogenesis is affected only by cytoplasmic translation inhibitors. These preliminary data seem to suggest that galactono-γ-lactone oxidase might be a multimeric enzyme, in which some polypeptidic chains could be synthesized in the cytosol and others in the mitochondria.

Germinability and fungal occurrence in seeds of Abies alba Mill. populations in southern Italy

Abstract Germination tests were carried out on seeds from three Italian populations of Abies alba. Seed germinability was up to 38%. HgCl2, NaClO and plant preservative mixture were used as seed‐sterilising agents. Despite chemical treatments, Papulaspora rubida and Chaetomium globosum were isolated. The possible role of these fungi in the physiology of silver fir seed germination process was discussed.