Gene interactions and epigenetic variation in transgenic plants

Confocal scanning light microscopy, which has revolutionized approaches to reconstructing three-dimensional images of living cells, has a new cousin: confocal Raman spectroscopy. This technique combines the use of confocal optics, to narrow detection to an extremely small volume (1 ttm3), with the ability of Raman spectroscopy to distinguish chemical bonds. Confocal Raman spectroscopy thus promises a highresolution approach to examining the composition of, for example, chromosomal domains. Preliminary results from use of this technique indicate that the protein: DNA ratio varies widely along banded polytene chromosomes, being highest in the bands, lower (but ~,erjr variable) in interband regions and lowest at the telomeres. Confocal Raman spectroscopy can be combined with immunofluorescence techniques to examine sites labelled by specific antibodies, and provides a useful check on the degree to which such labelling techniques perturb native structure. It may prove to be a vital link in correlating cytological observations with the results of genetic and biochemical analyses, a~