The pollen-specific gene Ntp303 encodes a 69-kDa glycoprotein associated with the vegetative membranes and the cell wall

The pollen-specific gene Ntp303 belongs to the class of late pollen specific genes. It is first transcribed directly after pollen mitosis. Biochemical properties, appearance and precise location of the NTP303 protein during pollen development and pollen tube growth were studied by amino-acid micro-sequencing, protein gel blotting and immuno-localization. Antisera were raised against recombinant proteins, encoded by sequences of the pollen-specific Ntp303 gene. The antibodies specifically recognized a 69-kDa glycoprotein. Electron-microscopic immuno-localization of the protein revealed the presence of high concentrations of the NTP303 protein at the vegetative plasma membranes that surround the vegetative cell, the generative cell and the sperm cells of pollen and pollen tubes. The generative plasma membranes of the generative cell and the sperm cells were negative. NTP303 protein was also present in the cell walls and in callose plugs. With this method it was shown that the NTP303 protein was already present in mid-bicellular pollen, after the first, asymmetrical pollen mitosis. Possible functions for the NTP303 protein are discussed in relation to its properties and its association with the vegetative plasma membranes. Received: 9 September 1999 / Revision accepted: 4 November 1999