Summary. Self-incompatibility in flowering plants is controlled by the S-gene, encoding stylar S (allele-specific) glycoproteins. In addition to three previously characterized Petunia hybrida S-proteins, we identified by N-terminal sequence analysis another stylar S-protein, cosegregating with the Sb-allele. Purified S-proteins reveal biological activity, as is demonstrated for two of them by the allele-specific inhibition of pollen tube growth in vitro. Moreover, the four isolated S-proteins are ribonucleases (S-RNases). Specific activities vary from 30 ($1) to 1000 (82) units per min per mg protein. We attempted to investigate the functionality of the carbohydrate portion of the S-RNases. Deglycosylation studies with the enzyme peptide-N-glycosidase F (PNGase F) reveals differences in the number of N-linked glycan chains present on the four S-RNases. Variability in the extent of glycosylation accounts for most of the molecular weight differences observed among these proteins. By amino acid sequencing, the positions of two of the three N-glycosylation sites on the S2-RNase could be located near the N-terminus. Enzymic removal of the glycan side chains has no effect on the RNase activity of native S-RNases. This suggests another role of the glycan moiety in the self-incompatibility mechanism.

The androecium of the Caryophyllaceae is varied, ranging from a two-whorled condition to a single stamen. A number of species belonging to the three subfamilies, CaryophylIoideae, Alsinoideae and Paronychioideae have been studied ontogenetically with the SEM to understand their peculiar androecial development in the brooder context of the Caryophyllales alliance. Although patterns of initiation are highly variable among species, there are three ontogenetic modes of stamen initiation: all stamens simultaneous within a whod, the antepatalous stamens simultaneous and the antesepalous sequentially with a reversed direction, or both whorls sequentially with or without a reversed direction. The most common floral (ontogeneUc) sequence of the Caryophyllaceae runs as follows: five sepals (in a 2/5 sequence), the stamens in front of the three inner sepals successively, stamens opposite the two outermost sepals, five antepatalous stamens (simultaneously or in a reversed spiral superimposed on the spiral of the antesepalous stamens), five outer sterile (petaloid) organs arising before, simultaneously or after the antesepalous stamens, often by the division of common pdmordia. A comparison with the floral configurations of the Phytolaccaceae and Molluginaceae indicates that the outer pataline whorl of the Caryophyllaceae corresponds posiUonally to the alternisepalous stamens of some Phytolacca, such as P. dodecandra. The difference with P. dodecandra lies in the fact that an extra inner or outer whorl is formed in the Caryophyllaceae, in alternation with the sepals. A comparable arrangement exists in the Molluginaceae, though the initiation of stamens is centrifugal. A comparison of floral ontogenies and the presence of reduction series in the Caryophyllaceae support the idea that the pentamerous arrangement is derived from a trimerous prototype. Petals correspond to sterilized stamens and are comparable to two stamen pairs opposite the outer sepals and a single stamen alternating with the third and fifth sepals. Petals are often in a state of reduction; they may be confused with staminodes and they often arise from common stamenpatal primordia. The antesepalous stamen whorl represents an amalgamation of two whorls: initiation is reversed with the stamens opposite the fourth and fifth formed sepals arising before the other, while the stamens opposite the first and second formed sepals are frequently reduced or lost. Reductive trends are correlated with the mode of initiation of the androecium, as well as changes in the number of carpals, and affect the antesepalous and antepatalous whorls in different proportions. It is concluded that the androecium of the Caryophyllaceae is pseudodiplostemon0us and is not comparable to diplostemonous forms in the Dilleniidae an.d Rosidae. The basic floral formula of Caryophyllaceae is as follows: sepals 5-patals 5 (sterile stamens) -antesepalous stamens 3-1-2 -antepatalous stamens 5 gynoecium 5.Key words: Androecium --Caryophyllaceae--Floral development --Gynoecium --Petals --Pseudodiploste...

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