Environmental and transgene expression effects on the barley seed proteome

The barley (Hordeum vulgare) cultivar Golden Promise is no longer widely used for malting, but is amenable to transformation and is therefore a valuable experimental cultivar. Its characteristics include high salt tolerance, however it is also susceptible to several fungal pathogens. Proteome analysis was used to describe the water-soluble protein fraction of Golden Promise seeds in comparison with the modern malting cultivar Barke. Using 2D-gel electrophoresis to visualise several hundred proteins in the pH ranges 4-7 and 6-11, 16 protein spots were found to differ between the two cultivars. Eleven of these were identified by mass spectrometric peptide mass mapping, including an abundant chitinase implicated in defence against fungal pathogens and a small heat-shock protein. To enable a comparison with transgenic seed protein patterns, differences in spot patterns between field and greenhouse-grown seeds were analysed. Four spots were observed to be increased in intensity in the proteome of greenhouse-grown seeds, three of which may be related to nitrogen availability during grain filling and total protein content of the seeds, since they also increased in field grown seeds supplied with extra nitrogen. Finally, the fate of transgene products in barley seeds was followed. Spots containing two green fluorescent protein constructs and the herbicide resistance marker phosphinothricin acetyltransferase were observed in 2D-gel patterns of transgenic seeds and identified by mass spectrometry. Phosphinothricin acetyltransferase was observed in three spots differing in pI suggesting that post-translational modification of the transgene product had occurred.