Plants treated with pWSRI:SpPI were fixed, imbedded and sectioned for in situ hybridization. (a, b) Hybridization with antisense RNA SpPI probe. a. Longitudinal section showing third whorl stamen and third whorl carpel. Strong SpPI expression is present in tapetal cells in stamen, whereas no detectable staining in the carpel. b. Inflorescence cluster with female (f) and early male flower. SpPI is detected in stamen primordium. c. Hybridization with antisense RNA SpAP3 probe. Cross section through a single flower with three stamen and one carpel in third whorl. Strong SpAP3 expression is detected in developing stamen. SpAP3 expression is absent in dehiscing stamen. No discernible SpAP3 staining in carpel. d. Hybridization with antisense SpAG probe. Cross section of flower with stamen and carpel. Strong SpAG expression is detectable in both organs. e. Hybridization with sense RNA SpPI probe. Abbreviations: st, stamen; c, carpel; f, female; m, male.