Royal Society Publishing

Pollen-Wall Proteins: Physicochemical Characterization and Role in Self-Incompatibility in Cosmos bipinnatus

B. J. Howlett, R. B. Knox, J. D. Paxton, J. Heslop-Harrison

Abstract

Fresh pollen of C. bipinnatus was extracted for 45 min in an isotonic mannitol-CaCl$_{2}$ medium that preserved pollen viability. The pollen-wall diffusates after partial purification by ammonium sulphate precipitation and gel filtration contained more than 7 protein bands by polyacrylamide gel electrophoresis. Two fractions contained demonstrable carbohydrate, suggesting they are glycoproteins. After SDS gel electrophoresis, many bands were obtained, the 2 major fractions having estimated (relative) molecular masses of 11 500 and 30 000. Gel patterns of C. bipinnatus pollen diffusate were compared with those from ragweed diffusate and antigen E. The pollen-wall proteins are implicated in the control of self incompatibility. In compatible matings, most pollen tubes had grown through the style to the ovary within 60 min after pollination. After self pollination, the pollen tube is arrested on the stigma surface, and the callose rejection response was detected within 15 min of pollination. Self incompatibility was partially overcome (to ca. 27% of compatible seed set) with pollen mixes of killed compatible and fresh self pollen. These could be replaced with equal effect by applying compatible pollen-wall diffusate (containing 1 mg/ml protein) followed by self pollination. The active proteins are heat stable, and include an antigen E-like fraction with partial immunological identity to the ragweed allergen.

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