Dynein related polypeptides during pollen tube growth

Nicotiana tabacum pollen tubes contain two high molecular weight polypeptides (about 400 kDa) which are specifically expressed during pollen germination and pollen tube growth. The high molecular weight doublet resembles the dynein heavy chains in some biochemical properties. Sedimentation profiles of pollen tube extracts show that the high molecular weight bands have sedimentation coefficients of 22 S and 12 S respectively. ATPase assay of sedimentation fractions shows an activity ten times higher when stimulated by the presence of bovine brain microtubules in fractions containing the 22 S high molecular weight polypeptide. Both these high molecular weight polypeptides can bind microtubules in an ATP-dependent fashion. A mouse antiserum (Dy-l) to a synthetic peptide reproducing the sequence of the most conserved ATP-binding site among dynein heavy chains recognized the two high molecular weight polypeptides. Therefore these polypeptides have epitopes immunologically related to the ATP binding sites of dynein heavy chains. immunofluorescence studies using the Dy-l antibody showed punctate structures, with a characteristic distribution pattern depending on the tube length. Biochemical evidence confirmed the presence of DHC related bands in the pollen tube membrane fraction.