A NICOTIANA-TABACUM MESSENGER-RNA ENCODING A 69-KDA GLYCOPROTEIN OCCURRING ABUNDANTLY IN POLLEN TUBES IS TRANSCRIBED BUT NOT TRANSLATED DURING POLLEN DEVELOPMENT IN THE ANTHERS

Regulation of expression of a 69-kDa glycoprotein which occurs abundan tly in tobacco (Nicotiana tabacum L.) pollen tubes but is absent in un germinated pollen has been studied in vitro by means of a coupled tran slation/glycosylation system with RNA isolated from various stages of pollen development. Pollen mRNA could be translated in a rabbit reticu locyte lysate and the products glycosylated with canine pancreatic mic rosomal membranes. The electrophoretic pattern of translation products obtained with pollen-tube RNA showed a prominent polypeptide with an apparent molecular mass of 58 kDa. In the presence of the canine pancr eatic microsomal membranes this polypeptide was glycosylated, producin g the 69-kDa glycoprotein. The presence of mRNA encoding the 58-kDa pr ecursor polypeptide was also demonstrated in ungerminated pollen and i n young mid-binucleate pollen isolated from anthers. Initiation of syn thesis of the 69-kDa glycoprotein at the onset of pollen germination t hus occurs through unmasking of the mRNA transcribed during pollen dif ferentiation and stored during pollen maturation and dormancy in an in active state.