Transcript profiling of two potato cultivars during glycoalkaloid-inducing treatments shows differential expression of genes in sterol and glycoalkaloid metabolism.

Steroidal glycoalkaloids (SGA) are sterol-derived neurotoxic defence substances present in several members of the Solanaceae. In the potato (Solanum tuberosum), high SGA levels may render tubers harmful for consumption. Tuber SGA levels depend on genetic factors, and can increase as a response to certain stresses and environmental conditions. To identify genes underlying the cultivar variation in tuber SGA levels, we investigated two potato cultivars differing in their SGA accumulation during wounding or light exposure; two known SGA-inducing treatments. Using microarray analysis coupled to sterol and SGA quantifications, we identified a small number of differentially expressed genes that were associated with increased SGA levels. Two of these genes, encoding distinct types of sterol Δ24-reductases, were by sense/antisense expression in transgenic potato plants shown to have differing roles in sterol and SGA metabolism. The results show that an increased SGA level in potato tubers during both wounding and light exposure is mediated by coordinated expression of a set of key genes in isoprenoid and steroid metabolism, and suggest that differences in this expression underlie cultivar variations in SGA levels. These results may find use within potato breeding and quality assessment.

Analysis of strawberry volatiles using comprehensive two-dimensional gas chromatography with headspace solid-phase microextraction.

The aims of the current study were to develop an enantioselective multi-dimensional gas chromatography (GC x GC) method for the examination of strawberry volatiles and to use this method to make comparisons between the volatile profiles of different cultivars and between fresh picked and post-harvest berries of the same cultivar. Strawberry volatiles were sampled using solid-phase microextraction (SPME), and the repeatability and reproducibility of this method was examined. Semi-quantitative analysis of the volatiles was conducted using the relatively new technique of comprehensive multi-dimensional gas chromatography, using enantioselective (chiral) columns for the differentiation of analyte enantiomers. Chiral GC x GC facilitated the detection of key enantiomers in strawberry flavour. The (-)-enantiomer of 2,5-dimethyl-4-hydroxy-(2H)-furan-3-one (DMHF) and the S-enantiomer of linalool were tentatively identified as the predominant forms in both the cultivars Selva and Adina. The compounds benzaldehyde and methyl hexanoate were shown to decrease in post-harvest berries, whilst DMHF and nerolidol increased upon storage.