Adnation

Abstract: Basal asterid families, and to a lesser extent the asterids as a whole, are characterized by a high variation in petal and stamen morphology. Moreover, the stamen number, the adnation of stamens to petals, and the degree of sympetaly vary considerably among basal asterid taxa. The B group genes, members of the APETALA3 (AP3) and PISTILLATA (PI) gene lineages, have been shown to specify petal and stamen identities in several core eudicot species. Duplicate genes in these lineages have been shown in some cases to have diversified in their function; for instance in Petunia, a PI paralog is required for the fusion of stamens to the corolla tube, illustrating that such genes belonging to this lineage are not just involved in specifying the identity of the stamens and petals but can also specify novel floral morphologies. This motivated us to study the duplication history of class B genes throughout asterid lineages, which comprise approximately one-third of all flowering plants. The evolutionary history of the PI gene subfamily indicates that the two genes in Petunia result from an ancient duplication event, coinciding with the origin of core asterids. A second duplication event occurred before the speciation of basal asterid Ericales families. These and other duplications in the PI lineage are not correlated with duplications in the AP3 lineage. To understand the molecular evolution of the Ericales PI genes after duplication, we have described their expression patterns using reverse transcription polymerase chain reaction and in situ hybridization, reconstructed how selection shaped their protein sequences and tested their protein interaction specificity with other class B proteins. We find that after duplication, PI paralogs have acquired multiple different expression patterns and negative selective pressure on their codons is relaxed, whereas substitutions in sites putatively involved in protein-protein interactions show positive selection, allowing for a change in the interaction behavior of the PI paralogs after duplication. Together, these observations suggest that the asterids have preferentially recruited PI duplicate genes to diverse and potentially novel roles in asterid flower development.

Abstract: which become reflexed in the fruit, and its rim bears a series of small, triangular bracts, which are sharply delimited from the perianth segments. Vascular anatomy indicates that there is a short floral tube formed by the adnation and connation of the bases of the stamens and perianth segments. The inner side of this floral tube forms an extensive cylindrical nectary; the outer si'de is adnate to the receptacle. There are usually five carpels, each bearing a single ovule. Carpel tips are free, but their bases are congenitally connate. During ontogeny, the adaxial faces of the carpels grow together, forming a solid style. The base of the ovary is partially divided into locules by small partitions, which represent the fused margins of connate carpels. The tip of the floral receptacle (residual meristem) becomes a convex body which enlarges in the fruit, filling that portion of the ovary cavity not occupied by seeds. The superior ovary and the columella formed in the fruit are probably primitive characteristics, but in all other respects the flower of P. aculeata appears to be advanced. It is a product of evolutionary reduction.

Abstract: The present paper deals with certain aspects of morphology and anatomy of the Saururaceae. Floral anatomy and embryology suggest a close relationship among the genera. In floral anatomy the genus Saururus is the least specialized and Anemopsis the most highly specialized. Structure and morphology of inflorescence and also flower suggest the manifestation of certain evolutionary trends, probably guided by reduction, cohesion and adnation. Origin of inferior ovary in the Saururaceae is discussed. Carpels and nature of placentation show certain primitive features. Origin and evolution from apocarpous condition to syncarpous condition of carpels are briefly discussed. Further details will be presented in a separate paper. M. V. S. RAJU, Department of Biology, University of Saskatchewan, Saskatoon, Saskatchewan, Canada.