A SHORT SEVERE HEAT-SHOCK IS REQUIRED TO INDUCE EMBRYOGENESIS IN LATEBICELLULAR POLLEN OF BRASSICA-NAPUS L

Until now it has been considered that in rape seed (Brassica napus) on ly late uninucleate microspores and early bicellular pollen are compet ent for induction of in vitro embryogenesis. Here we describe that pol len isolated at the late bicellular stage call also be induced to unde rgo embryogenesis. By the application of an additional short and more severe heat stress treatment, DNA synthesis was initialed in both gene rative and vegetative nuclei, but only vegetative cells were able to c omplete the cell cycle and to divide further. The ability of late bice llular pollen to respond to embryogenic induction treatment was accomp anied by rearrangements of the microtubulular cytoskeleton and by the nuclear localization of 70 kDa heat shock proteins (HSP70). These find ings confirm earlier observations that there is a strong correlation b etween the induction of embryogenesis and the synthesis and nuclear lo calization of HSP70.