Immunocytochemical distribution of polygalacturonase and pectins in styles of distylous and homostylous Turneraceae

Abstract

Distyly is a plant breeding system in which two self-incompatible, but cross-compatible, floral morphs occur within populations. The morphs differ in having a reciprocal arrangement of styles and anthers. Little or nothing is known of the proteins involved in self-incompatibility for any distylous species. Here we show that a 35 kDa putative polygalacturonase is specific to the transmitting tissue of short-styled plants of five species in series Turnera. The polygalacturonase was not detected in styles of long-styled plants, or in styles of five homostylous self-compatible species in this series of the genus. It is also absent from two X-ray generated mutants and a spontaneous somatic homostylous mutant that arose on a short-styled plant and whose style does possess this polygalacturonase. Three more distantly related species in the Turneraceae were investigated. Turnera weddelliana (series Salicifoliae) does possess the polygalacturonase; however, T. diffusa (series Microphyllae), and Piriqueta caroliniana, showed no evidence of possessing this polygalacturonase using immunocytochemistry. Polygalacturonase assays revealed activity in styles of long- and short-styled plants, but showed no activity of the 35 kDa style polygalacturonase. The distribution of pectins in styles and pollen tubes revealed no difference between the long- and short-styled morphs. Methyl-esterified pectins occur throughout the style tissues, except in the transmitting tissue. The transmitting tissue possesses unesterified pectins that could provide a substrate for polygalacturonase activity. We propose that the style polygalacturonase might act in a complementary manner, allowing pollen of long-styled plants to grow through short styles or, alternatively, oligogalacturonide products of polygalacturonase activity might play a role in signalling compatible responses.