HIGH LEVEL OF [alpha]-DIOXYGENASE IN SHORT STYLES OF DISTYLOUS TURNERA SPECIES

To identify proteins responsible for self-incompatibility and/or other dimorphisms in distylous species of Turnera, we used SDS-polyacrylamide gel electrophoresis to compare protein profiles of long and short styles. We detected a prominent 68-kD protein in styles of short- but not long-styled plants. This result was consistent in all five of the distylous species examined, except in a more divergent species, Piriqueta caroliniana, in which short styles did not express the protein but long styles may exhibit a low level of expression. Sequencing of tryptic peptides, genomic DNA, and phylogenetic analyses revealed the 68-kD protein to be an α-dioxygenase. Immunoblotting using antiserum against a pathogen-induced α-dioxygenase from tobacco further confirmed that the 68-kD protein is an α-dioxygenase. Using immunoblotting, we could not detect the α-dioxygenase in other floral or vegetative organs, in styles of homostylous species, or in three mutants. The α-dioxygenase reaches detectable levels in short styles 1 d before anthesis and high levels at flowering. Immunocytochemical analysis localized the α-dioxygenase to the transmitting tissue of short styles in all three species examined. An α-dioxygenase assay using crude style extracts revealed twice the activity for short compared with long styles. The tissue-specific and temporal patterns of expression, as well as its consistent appearance in short-styled plants of all Turnera species examined, indicates that the α-dioxygenase plays some as yet unspecified role in distyly. [PUBLICATION ABSTRACT] Keywords: distyly, Turnera, α-dioxygenase.