The antioxidative capacities of a number of Rubus species of varied pigmentation have been investigated. In addition, total phenol, anthocyanin and ascorbic acid contents have been determined. Two methods to assess the antioxidant potential of fruit juices have been used. The antioxidant capacities of the fruit ranged from 0 to 25.3 mmol Trolox equivalents g À1 (TEAC) or from 190 to 66 000 mmol l À1 ferric reducing antioxidant power (FRAP). Ascorbic acid contributes only minimally to the antioxidant potential of Rubus juices (`10%, TEAC). There are apparent linear relationships between antioxidant capacity (assessed as both TEAC and FRAP) and total phenols (r xy = 0.6713 and 0.9646 respectively). Also, anthocyanin content has a minor in¯uence on antioxidant capacity (r xy = 0.3774, TEAC; r xy = 0.5883, FRAP). The sample with the highest antioxidant capacity (Rubus caucasicus) had the highest phenol content, but only a low percentage was represented by anthocyanins. The present study demonstrates the potential of certain wild Rubus species, notably R caucasicus, for improvement of nutritional value through germplasm enhancement programmes.

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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.

A molecular approach has been used to study the role of polyamines in plant development by manipulating the expression of the S‐adenosylmethionine decarboxylase (SAMDC) gene. SAMDC is a key enzyme involved in the biosynthesis of the polyamines spermidine and spermine and is also known to influence the rate of biosynthesis of ethylene. Previously, a cDNA clone of the SAMDC gene of potato has been isolated and characterized. This cDNA clone has been used to make antisense and sense SAMDC constructs under the control of the 35S CaMV or tetracycline‐inducible promoters. Agrobacterium‐mediated transformation has been used to produce transgenic potato plants with the engineered antisense and sense SAMDC genes in order to downregulate or overexpress the SAMDC transcript, respectively. Decreases or increases in the level of SAMDC transcript in the antisense and sense transgenic plants were observed, respectively. Antisense transgenic plants which expressed the engineered SAMDC gene constitutively under the control of the 35S CaMV promoter with a duplicated enhancer region showed a range of stunted phenotypes with highly branched stems, short internodes, small leaves and inhibited root growth. The abnormal characteristics of the antisense plants correlated with the altered levels of SAMDC transcript, SAMDC activity, polyamine content and rate of ethylene evolution. Attempts to produce sense transgenic plants with the 35S SAMDC sense construct were unsuccessful indicating that a constitutive overexpression of the engineered SAMDC is lethal to the plants. When antisense and sense SAMDC transgenes were expressed under the control of a tetracycline‐inducible promoter a number of transgenic plants were produced. In these antisense and sense plants, significant changes in the level of SAMDC transcript, SAMDC activity and free polyamine content were observed on tetracycline‐induction of detached leaves.

No abstract

Metabolite profiling has been carried out to assess the compositional changes occurring in potato tubers after genetic modifications have been made to different metabolic pathways. Most major features in the (1)H NMR and HPLC-UV profiles of tuber extracts have been assigned. About 40 GM lines and controls belonging to 4 groups of samples (derived from cv. Record or cv. Desirée and modified in primary carbon metabolism, starch synthesis, glycoprotein processing, or polyamine/ethylene metabolism) were analyzed. Differences were assessed at the level of whole profiles (by PCA) or individual compounds (by ANOVA). The most obvious differences seen in both NMR and HPLC-UV profiles were between the two varieties. There were also significant differences between two of the four Desirée GM lines with modified polyamine metabolism and their controls. Compounds notably affected were proline, trigonelline, and numerous phenolics. However, that modification gave rise to a very abnormal phenotype. Certain lines from the other groups had several compounds present in significantly higher or lower amounts compared to the control, but the differences in mean values amounted to no more than a 2-3-fold change: in the context of variability in the whole data set, such changes did not appear to be important.

The influence of urease activity on N distribution and losses after foliar urea application was investigated using wild-type and transgenic potato (Solanum tuberosum cv Désirée) plants in which urease activity was down-regulated. A good correlation between urease activity and 15 N urea metabolism (NH 3 accumulation) was found. The general accumulation of ammonium in leaves treated with urea indicated that urease activity is not rate limiting, at least initially, for the assimilation of urea N by the plant. It is surprising that there was no effect of urease activity on either N losses or 15 N distribution in the plants after foliar urea application. Experiments with wild-type plants in the field using foliar-applied 15 N urea demonstrated an initial rapid export of N from urea-treated leaves to the tubers within 48 h, followed by a more gradual redistribution during the subsequent days. Only 10% to 18% of urea N applied was lost (presumably because of NH 3 volatilization) in contrast to far greater losses reported in several other studies. The pattern of urease activity in the canopy was investigated during plant development. The activity per unit protein increased up to 10-fold with leaf and plant age, suggesting a correlation with increased N recycling in senescing tissues. Whereas several reports have claimed that plant urease is inducible by urea, no evidence for urease induction could be found in potato.Urea is the most frequently used N fertilizer globally. For example, in China and India urea accounted for 53% and 83%, respectively, of total N fertilizer consumption in 1998. Together, both countries consumed 41% of all N fertilizer used worldwide in that year (Food and Agriculture Organization of the United Nations, 1998).The reaction catalyzed by urease is essential to make urea N accessible to plants (Gerendás et al., 1999). Urease activity has been detected in many plants (Frankenberger and Tabatabai, 1982; Hogan et al., 1983; Witte and Medina-Escobar, 2001) and is reported to be inducible by urea in rice (Oryza sativa; Matsumoto et al., 1966), jack bean (Canavalia ensiformis; Matsumoto et al., 1968), and barley (Hordeum vulgare), where in addition the formation of different urease isoforms was observed (Chen and Ching, 1988).Urease catalyzes the hydrolysis of urea to carbamate and NH 3 . Carbamate is unstable and yields a second molecule of NH 3 and carbonic acid. The release of NH 3 during the urease reaction leads to a pH rise because at neutral pH most NH 3 becomes protonated [NH 3 ϩ H ϩ 7 NH 4 ϩ ]. Gaseous NH 3 may escape from the system (volatilize) especially when the chemical equilibrium is driven toward NH 3 at higher pH.Urea can also be supplied to plants through the foliage, facilitating optimal N management, which minimizes N losses to the environment (Haverkort and MacKerron, 2000) without affecting yield (Giroux, 1984; Millard and Robinson, 1990). Most plants absorb foliar applied urea rapidly (Wittwer et al., 1963; Nicoulaud and Bloom, 1996) and hydrolyze the urea in the cytosol. ...

A range of studies have compared the level of nutritionally relevant compounds in crops from organic and nonorganic farming systems, but there is very limited information on the effect of farming systems and their key components on the protein composition of plants. We addressed this gap by quantifying the effects of different farming systems and key components of such systems on the protein profiles of potato tubers. Tuber samples were produced in the Nafferton factorial systems study, a group of long-term, replicated factorial field experiments designed to identify and quantify the effect of fertility management methods, crop protection practices and rotational designs used in organic, low input and conventional production systems. Protein profiles were determined by 2-DE and subsequent protein identification by HPLC-ESI-MS/MS. Principal component analysis of 2-DE data showed that only fertility management practices (organic matter vs. mineral fertiliser based) had a significant effect on protein composition. Quantitative differences were detected in 160 of the 1100 tuber proteins separated by 2-DE. Proteins identified by MS are involved in protein synthesis and turnover, carbon and energy metabolism and defence responses, suggesting that organic fertilisation leads to an increased stress response in potato tubers.