The differential expression of a heat shock promoter in floral and reproductive tissues

A detailed histochemical analysis of the expression of the soybean small he at shock protein gene promoter, GmHSP 17.5E, fused to the GUS reporter gene , has been made in all organs and tissues of the flower as a function of st age of development and heat stress. This promoter is not uniformly expresse d after a heat shock in all floral tissues and organs. Expression is seen a t all stages of development in the sepals but not in the petals. The expres sion pattern in the pistil and in anthers is complex. Heat stress-induced G US staining is seen in the style and upper portion of the ovary, but not in the stigmatic papillae or in the lower part of the ovary or in ovules. In stamens the heat shock response is seen in the filament and in the extensio n of the vascular tissue from the filament into the anther. No induction is seen in other tissues of the anther or in microspores or pollen at any sta ge of development. Vegetative organs in contrast are more uniform in the be at shock inducibility of GUS activity. Based on evidence from transient ass ays after microprojectile particle bombardment of the GmHSP 17.5E/GUS const ruct into pollen, it is likely that the gene is transcriptionally in an ina ctive configuration in pollen nuclei in stably transformed transgenic plant s. These results are discussed with reference to other information in the l iterature.