REEVALUATION OF THE ROLE OF A TRANSMITTING TRACT-SPECIFIC GLYCOPROTEIN ON POLLEN-TUBE GROWTH

It has been proposed that a stylar glycoprotein, the transmitting tiss ue-specific (TTS) protein isolated from Nicotiana tabacum, serves both as a growth stimulant, by providing a source of nutrients, and as an attractant for pollen tubes during their growth through the style. Wor king with a galactose-rich style glycoprotein (GaRSGP) that is the N. alata homologue (97% homology) of the TTS protein, a series of experim ents, similar to those done with the TTS protein, was performed. Evide nce was found for inhibition of pollen tube growth at high concentrati ons, but no evidence was found for stimulation of growth at concentrat ions up to 2 mg ml(-1). No effect as a pollen tube attractant was dete cted. The discrepancies in the features and functionality between thes e homologous glycoproteins in the closely related Nicotiana species wa rrants further investigation before a general function is assigned to these molecules.