Georgios Tsaniklidis

l -Ascorbic acid metabolism in parthenocarpic and seeded cherry tomatoes

The auxin treatment in tomato plants during anthesis has been extensively used for setting fruits in adverse climatic conditions (e.g., low temperatures and inadequate light), which is well known that reduces pollen availability and fertility. Since auxin application may affect fruit composition and quality, we examined l-ascorbic acid metabolism in seeded fruit (set by natural pollination) and parthenocarpic fruit (set by auxin) in cherry tomato cv. Conchita. Specifically, we studied the oxidized and total ascorbic acid contents, the expression of all characterized genes of l-ascorbic acid metabolism, the activity of ascorbate peroxidase and dehydroascorbate reductase and the immunolocalization of ascorbate peroxidase. Differences were detected between seeded and parthenocarpic fruits, in the expression of some of the genes of ascorbic acid metabolism. However, strong presence of l-ascorbic acid peroxidase protein was detected on the developing seeds. Our data indicate that induced parthenocarpy in auxin treated plants has a significant influence in ascorbic acid metabolism comparing to seeded tomato fruits.

Induced parthenocarpic cherry tomato fruits did not shown significant differences in l -ascorbate content but showed different pattern in GalLDH and GME expression

Parthenocarpy in tomato is often induced by auxins to overcome fertilization problems due to low temperatures. To estimate the effect of this agronomical practice on the physiology and dietary value of cherry tomato fruits we determined l-ascorbic acid, the expression and immunolocalization of galactono 1,4 lactone dehydrogenase and the expression of GDP-mannose 3′,5′-epimerase, key genes in l-ascorbic acid biosynthesis. The levels of l-ascorbic acid did not differ between seeded and parthenocarpic fruits while the relative expression of galactono 1,4 lactone dehydrogenase and GDP-mannose 3′,5′-epimerase gene transcripts showed some significant differences between seeded and parthenocarpic fruits. The galactono 1,4 lactone dehydrogenase immunohistolocalization signal was stronger in the ovules and mature embryos of seed-containing fruits. Our data suggest that although there were differences in the expression of the studied genes and in enzyme localization, these did not cause differences in the l-ascorbic acid content of parthenocarpic fruits produced by auxin application.

Seeded and Parthenocarpic Cherry Tomato Fruits Exhibit Similar Sucrose, Glucose, and Fructose Levels, Despite Dissimilarities in UGPase and SPS Gene Expression and Enzyme Activity

Farmers often resort to the production of auxin-induced parthenocarpic tomato fruits to overcome the adverse climatic conditions which are unfavorable for sufficient fertilization and to lengthen the production period. Even though this practice improves the out-of-season yield, it often undermines fruit quality. In the current study, we examined the effect of induced parthenocarpy in cherry tomato cv. Conchita on the concentration of the main sugars, and on the expression, the activity and the localization of UDP-glucose pyrophosphorylase (UGPase) and sucrose phosphate synthase (SPS), enzymes that are actively involved in sucrose metabolism. Minor differences were detected in sugar levels of seeded and parthenocarpic fruits, whereas considerable variances were found in transcript accumulation and enzyme activities of both UGPase and SPS. Moreover, both proteins were present in the developing seeds. Our data indicate that although induced parthenocarpy significantly influences sucrose metabolism, it has a negligible effect on sugar levels.

Spatial and temporal distribution of genes involved in polyamine metabolism during tomato fruit development.

Polyamines are organic compounds involved in various biological roles in plants, including cell growth and organ development. In the present study, the expression profile, the accumulation of free polyamines and the transcript localisation of the genes involved in Put metabolism, such as Ornithine decarboxylase (ODC), Arginine decarboxylase (ADC) and copper containing Amine oxidase (CuAO), were examined during Solanum lycopersicum cv. Chiou fruit development and maturation. Moreover, the expression of genes coding for enzymes involved in higher polyamine metabolism, including Spermidine synthase (SPDS), Spermine synthase (SPMS), S-adenosylmethionine decarboxylase (SAMDC) and Polyamine oxidase (PAO), were studied. Most genes participating in PAs biosynthesis and metabolism exhibited an increased accumulation of transcripts at the early stages of fruit development. In contrast, CuAO and SPMS were mostly expressed later, during the development stages of the fruits where a massive increase in fruit volume occurs, while the SPDS1 gene exhibited a rather constant expression with a peak at the red ripe stage. Although Put, Spd and Spm were all exhibited decreasing levels in developing immature fruits, Put levels maxed late during fruit ripening. In contrast to Put both Spd and Spm levels continue to decrease gradually until full ripening. It is worth noticing that in situ RNA-RNA hybridisation is reported for the first time in tomato fruits. The localisation of ADC2, ODC1 and CuAO gene transcripts at tissues such as the locular parenchyma and the vascular bundles fruits, supports the theory that all genes involved in Put biosynthesis and catabolism are mostly expressed in fast growing tissues. The relatively high expression levels of CuAO at the ImG4 stage of fruit development (fruits with a diameter of 3 cm), mature green and breaker stages could possibly be attributed to the implication of polyamines in physiological processes taking place during fruit ripening.

Gene transcript accumulation and in situ mRNA hybridization of two putative glutamate dehydrogenase genes in etiolated Glycine max seedlings

Abstract Glutamate dehydrogenase (EC 1.4.1.2) is a multimeric enzyme that catalyzes the reversible amination of α-ketoglutarate to form glutamate. We characterized cDNA clones of two Glycine max sequences, GmGDH1 and GmGDH2, that code for putative α- and β-subunits, respectively, of the NADH dependent enzyme. Temporal and spatial gene transcript accumulation studies using semiquantitative RT-PCR and in situ hybridization have shown an overlapping gene transcript accumulation pattern with differences in relative gene transcript accumulation in the organs examined. Detection of NADH-dependent glutamate dehydrogenase activity in situ using a histochemical method showed concordance with the spatial gene transcript accumulation patterns. Our findings suggest that although the two gene transcripts are co-localized in roots of etiolated soybean seedlings, the ratio of the two subunits of the active holoenzyme may vary among tissues.