FOURIER-TRANSFORM INFRARED MICROSPECTROSCOPY DETECTS CHANGES IN PROTEIN SECONDARY STRUCTURE ASSOCIATED WITH DESICCATION TOLERANCE IN DEVELOPING MAIZE EMBRYOS

Isolated immature maize (Zea mays L.) embryos have been shown to acqui re tolerance to rapid drying between 22 and 25 d after pollination (DA P) and to slow drying from 18 DAP onward. To investigate adaptations i n protein profile in association with the acquisition of desiccation t olerance in isolated, immature maize embryos, we applied in situ Fouri er transform infrared microspectroscopy. In fresh, viable, 20- and 25- DAP embryo axes, the shapes of the different amide-l bands were identi cal, and this was maintained after flash drying. On rapid drying, the 20-DAP axes had a reduced relative proportion of or-helical protein st ructure and lost viability. Rapidly dried 25-DAP embryos germinated (7 4%) and had a protein profile similar to the fresh control axes. On sl ow drying, the alpha-helical contribution in both the 20- and 25-DAP e mbryo axes increased compared with that in the fresh control axes, and survival of desiccation was high. The protein profile in dry, mature axes resembled that after slow drying of the immature axes. Rapid dryi ng resulted in an almost complete loss of membrane integrity in the 20 -DAP embryo axes and much less so in the 25-DAP axes. After slow dryin g, low plasma membrane permeability ensued in both the 20- and 25-DAP axes. We conclude that slow drying of excised, immature embryos leads to an increased proportion of cu-helical protein structures in their a xes, which coincides with additional tolerance of desiccation stress.