Differentiation of Apricots of Different Geographic Origin in Central and Southern Europe by Applying 87Sr/86Sr Analysis: Potential and Limitations

Consumers prefer food commodities of certain origins over the same products of other provenances and are willing to pay higher prices for them. Thus, it is possible to increase profit simply by giving an incorrect geographic origin to a product. To effectively control the declared geographic origin of food, the product itself has to be investigated to discover whether it actually originates from the declared origin, or if it has been mislabeled. Conventionally, control of a geographic origin is conducted by stable isotope analysis of the main elements, which has proven to be successful in numerous cases, but often reference data have to be produced anew for every harvest to control, resulting in additional costs and delays. Applying entirely geogenic parameters for the control of provenance requires reference data to be produced only once. As they do not vary between years and harvests, they can often be used for different (food) commodities. Here, we investigate whether the geographic origin of apricot samples can be controlled by their ⁸⁷Sr/⁸⁶Sr ratios measured by TIMS. The results show that Slovak and Hungarian apricots can be differentiated from the Wachau apricots, a well-known regional Austrian brand, and those from other regions in Austria, even though the differentiation from the latter is only partial. ⁸⁷Sr/⁸⁶Sr investigations can be a very potent tool; however, its success depends on the exact question that needs to be answered.

Effect of heat stress on polyamine metabolism in proline-over-producing tobacco plants

The effect of heat stress on the accumulation of proline and on the level of polyamines (PAs) in tobacco plants was investigated. Responses to heat stress were compared in the upper and lower leaves and roots of tobacco plants that constitutively over-express a modified gene for the proline biosynthetic enzyme Δ1-pyrroline-5-carboxylate synthetase (P5CSF129A) and in the corresponding wild-type. In the initial phases of heat stress (after 2h at 40°C), the accumulation of proline increased in the wild type but slightly decreased in the transformants. The response to heat stress in proline-over-producing tobacco plants involved a transient increase in the levels of free and conjugated putrescine (Put) and in the levels of free spermidine (Spd), norspermidine (N-Spd) and spermine (Spm) after a 2-h lag phase, which correlated with stimulation of the activity of the corresponding biosynthetic enzymes. Diamine oxidase (DAO) activity increased in both plant genotypes, most significantly in the leaves of WT plants. Polyamine oxidase (PAO) activity increased in the roots of WT plants and decreased in the leaves and roots of the transformants. After 6h of heat stress, proline accumulation was observed in the transformants, especially in the lower leaves; much more modest increase was observed in the WT plants. A decrease in the levels of free and conjugated Put coincided with down-regulation of the activity of ornithine decarboxylase and marked stimulation of DAO activity in the leaves and roots of the transformants. PAO activity increased in the roots of the transformants but decreased in the leaves. Conversely, in WT tobacco subjected to 6h of heat stress, slight increases in free and conjugated PA levels were observed and the activity of DAO only increased in the roots; PAO activity did not change from the value observed during the initial phase of heat stress. 6 Hours' heat stress had no effect on the level of malondialdehyde (MDA; a product of lipid peroxidation), in the upper leaves of either genotype. After a recovery period (2h at 25°C), most of the studied parameters exhibited values comparable to those observed in untreated plants. The coordination of the proline and polyamine biosynthetic pathways during heat stress conditions is discussed.

Comparison of hormonal responses to heat, drought and combined stress in tobacco plants with elevated proline content

In order to test the possibility of improving tolerance to heat and drought (alone and in combination) by elevation of the osmoprotectant proline (Pro) content, stress responses were compared in tobacco plants constitutively over-expressing a gene for the Pro biosynthetic enzyme Δ(2)-pyrroline-5-carboxylate synthetase (P5CSF129A; EC 2.7.2.11/1.2.1.41) and in the corresponding wild-type. Significantly enhanced Pro production in the transformant coincided with a more negative leaf osmotic potential (both at control conditions and following stress) and enhanced production of protective xanthophyll cycle pigments. Heat stress (40 °C) caused a transient increase in the level of bioactive cytokinins, predominantly N(6)-(2-isopentenyl)adenosine, accompanied by down-regulation of the activity of the main cytokinin degrading enzyme cytokinin oxidase/dehydrogenase (EC 1.4.3.18/1.5.99.12). No significant differences were found between the tested genotypes. In parallel, a transient decrease of abscisic acid was observed. Following drought stress, bioactive cytokinin levels decreased in the whole plants, remaining relatively higher in preferentially protected upper leaves and in roots. Cytokinin suppression was less pronounced in Pro transformants. Exposure to heat stress (40 °C for 2h) at the end of 10-d drought period strongly enhanced the severity of the water stress, as indicated by a drop in leaf water potential. The activity of cytokinin oxidase/dehydrogenase was strongly stimulated in upper leaves and roots of stressed plants, coinciding with strong down-regulation of bioactive cytokinins in whole plants. Combined heat and drought stress resulted in a minor decrease in abscisic acid, but only in non-wilty upper leaves. Both stresses as well as their combination were associated with elevation of free auxin, indolylacetic acid, in lower leaves and/or in roots. Auxin increase was dependent on the stress strength. After rehydration, a marked elevation of bioactive cytokinins in leaves was observed. A greater increase in cytokinin content in Pro transformants indicated a mild elevation of their stress tolerance.