Laser microprobe mass analysis was explored as a method for the detection at the cellular level of the phytoalexin glyceollin in soybean cotyledons infected with an incompatible race of Phy- tophthora megasperma f. sp. glycinea. For LAMMA® analysis 10 μm freeze microtome sections which were freeze-dried on copper grids were used. The LAMMA spectrum of glyceollin (isomer I) shows a characteristic peak at m/e = 321 which can be attributed to M-OH+. This peak was also present in the spectra of infected regions from a cotyledon but was completely absent in the spectra of uninfected tissue. One hundred and Fifty LAMMA spectra were taken along a line perpendicular to the border line of infection. A steep rise in glyceollin content toward the infected area was observed. This is the First time that such highly localized glyceollin accumulation has been shown at the cellular level. The results show that LAMMA analysis is suitable for the detection of organic molecules in biological tissues with high lateral resolution.
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