PROTEIN-SYNTHESIS IN TOBACCO POLLEN TUBES - PREFERENTIAL SYNTHESIS OFCELL-WALL 69-KDA AND 66-KDA GLYCOPROTEINS

One- and two-dimensional electrophoresis of Nicotiana tabacum pollen a nd pollen tube proteins confirmed that a new protein is preferentially synthesized during pollen germination and tube growth and becomes the most abundant protein in pollen tubes. Analysis of proteins extracted with sodium dodecyl sulfate (SDS) from different pollen tube fraction s showed that it is the most abundant non-covalently bound wall protei n, characterized by molecular mass of 69 kDa, pI between 7.9 and 8.2, and glycosylation with glucose and/or mannose. Amino acid analysis rev ealed relative abundance of serine, glutamic acid and glycine, but did not show the presence of hydroxyproline. According to all these chara cteristics, it cannot be classified as an extensin-like protein. Anoth er prominent wall-bound glycoprotein has a molecular mass of 66 kDa an d the same pl as the 69 kDa glycoprotein. These two glycoproteins are similar also in ConA binding, rate of synthesis, and rapid incorporati on into pollen tube walls. Their synthesis is strongly reduced by tuni camycin and this inhibition results in the occurrence of new polypepti des in the range of 57-61 kDa. Tunicamycin also inhibited pollen tube growth. At 10 ng ml-1 and 50 ng ml-1 the inhibitor reduced pollen tube mass after 24 h of culture by 30% and 85%, respectively. This indicat es that tobacco pollen presents a system highly sensitive to tunicamyc in and that cotranslational N-linked glycosylation on the rough endopl asmic reticulum is required for 66 and 69 kDa glycoprotein formation a nd for pollen tube growth. Although other proteins appear during polle n germination and tube growth, the new proteins occur at low levels an d seem to originate through modifications of preexisting polypeptides. In contrast to 69 and 66 kDa proteins, most proteins detected by [C-1 4]amino acid incorporation and fluorography of gels were not revealed by Coomassie blue staining.