Abstract: An in situ hybridization technique for localization of cahnodulin (CaM) mRNA in isolated entire embryo sacs and proembryos in Nicotiana tabacum L. cv. W38 has been developed. This technique can be applied to small amounts of materials in which a whole view of CaM mRNA distribution can be obtained. The authors revealed that CaM mRNA expression changes dramatically before and after fertilization. Especially interesting is that a prominent CaM mRNA band appears between the egg apparatus and polar nuclei temporarily during the period of pollination and fertilization. The band disappears just prior to fertilization and expands to a fan-shaped region that occupies the micropylar portion of the embryo sac. After fertilization, CaM mRNA accumulates in the elongated zygotes with higher concemration in their chalazal portion than in the micropylar portion. Such an asymmetrical pattern continues to manifest in the early proembryos. It is supposed that CaM mRNA may be involved in the early events and signaling steps associated with double fertilization and zygote polarization in higher plants.

Key words: Calmodulin mRNA, in sim hybridization, Embryo sac, Proembryo, Nicotiana tabacum