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Crop improvement by genetic modification remains controversial, one of the major issues being the potential for unintended effects. Comparative safety assessment includes targeted analysis of key nutrients and antinutritional factors, but broader scale-profiling or "omics" methods could increase the chances of detecting unintended effects. Comparative assessment should consider the extent of natural variation and not simply compare genetically modified (GM) lines and parental controls. In this study, potato (Solanum tuberosum) proteome diversity has been assessed using a range of diverse non-GM germplasm. In addition, a selection of GM potato lines was compared to assess the potential for unintended differences in protein profiles. Clear qualitative and quantitative differences were found in the protein patterns of the varieties and landraces examined, with 1,077 of 1,111 protein spots analyzed showing statistically significant differences. The diploid species Solanum phureja could be clearly differentiated from tetraploid (Solanum tuberosum) genotypes. Many of the proteins apparently contributing to genotype differentiation are involved in disease and defense responses, the glycolytic pathway, and sugar metabolism or protein targeting/storage. Only nine proteins out of 730 showed significant differences between GM lines and their controls. There was much less variation between GM lines and their non-GM controls compared with that found between different varieties and landraces. A number of proteins were identified by mass spectrometry and added to a potato tuber two-dimensional protein map. [ABSTRACT FROM AUTHOR]

Fruit starch reserves can be an important contributor to the sugar content of some ripe fruit, and despite the relatively high financial premiums (compared to other fruit) commanded by ripe strawberries, neither their starch or sugar biochemistry has been examined in detail. This study assessed the rate of starch biosynthesis and breakdown in developing strawberry and sought to determine the temporal changes in the activities of selected enzymes known to be involved in sucrose-starch interconversions. Scanning electron microscopy revealed that starch levels appeared greatest in immature strawberry (Fragaria×ananassa, cv. Elsanta) at 7 days postanthesis, as evidenced by a decrease in the number of cells containing starch granules as ripening progressed. Levels of key enzymes of starch and sugar metabolism estimated using Western blotting and enzyme activity analysis showed that activities did not correlate with antigen levels. In particular, enzyme activity recovery experiments indicated that losses were due to non-proteinaceous inhibitors, and in particular protein binding: highlighting the potential for misinterpretation of enzyme activity data gathered from ripening (strawberry) fruit tissue extracts. Consequently, in vitro experiments using [U-14C] glucose revealed that incorporation to starch is low (11%) at the earliest developmental stages when starch content is greatest. Starch synthesis rate then declines to non-detectable levels as fruit expand and ripen. These results show that starch accumulates extremely early in the fruit formation process and that starch degradation predominates during fruit growth and development. We estimate that breakdown of transient starch can contribute up to 3% of the sugar accumulated in ripe fruit. [ABSTRACT FROM AUTHOR]

The antioxidant status of potato (Solanum tuberosum L.) tubers of two genotypes. cv. Désirée and clone 10337de40 was investigated in relation to susceptibility to internal rust spot (IRS), a Ca2+-related physiological disorder. Concentrations of total calcium within the perimedulla tissue of tubers, grown with a restricted (1 mM CaCI2) Ca2+ supply, were similar in cv. Désirée (IRS resistant) and clone 10337de40 (IRS susceptible). A range of antioxidants was assayed in order to assess antioxidant status in both genotypes under the two Ca2+ treatments. Although no appreciable differences were detected between low Ca2+ and control treatments, certain antioxidants were present at significantly higher levels in the IRS resistant genotype. cv. Désirée. These included dehydroascorbate reductase (EC 1.8.5.1) activity (more than 100% higher), total glutathione content (ca 40% higher), glutathione reductase (EC 1.6.4.2) activity (almost 50% higher). peroxidase (EC 1.11.1.7) activity (ca 60% higher) and superoxide dismutase (EC 1.15.1.1) activity (almost 80% higher). There was no difference in ascorbate content. ascorbate free radical reductase activity (EC 1.6.5.4), α-tocopherol levels and catalase activity (EC 1.11.1.6) between the two genotypes. The possible relationship between resistance to IRS and a superior antioxidant status, found in cv. Désirée. is discussed. [ABSTRACT FROM AUTHOR]