COMPLEXITY AND GENETIC-VARIABILITY OF HEAT-SHOCK PROTEIN EXPRESSION IN ISOLATED MAIZE MICROSPORES

The expression of heat-shock proteins (HSPs) in isolated maize (Zea ma ys L.) microspores has been investigated using high-resolution two-dim ensional electrophoresis coupled to immunodetection and fluorography o f in vivo synthesized proteins. To this end, homogeneous and viable po pulations of microspores have been purified in sufficient amounts for molecular analysis from plants grown in controlled conditions. Appropr iate conditions for thermal stress application have been defined. The analysis revealed that isolated microspores from maize display a class ical heat-shock response characterized by the repression of the normal protein synthesis and the expression of a set of HSPs. A high complex ity of the response was demonstrated, with numerous different HSPs bei ng resolved in each known major HSP molecular weight class. However, t he extent of this heat-shock response is limited in that some of these HSPs do not accumulate at high levels following temperature elevation . Comparative analysis of the heat-shock responses of microspores isol ated from five genotypes demonstrated high levels of genetic variabili ty. Furthermore, many HSPs were detected in microspores at control tem perature, indicating a possible involvement of these proteins in polle n development at stages close to first pollen mitosis.