Antiserum against a stigma-exudate protein of tobacco, SE32, which was identical with PPAL, a beta-expansin-like protein specific to stigma, cross-reacted with another stigma-exudate protein, SE35

In the first step of pollination in tobacco, pollen grains attach to the st igma exudate, which we previously found to contain two major stigma-exudate proteins, SE32 (32 kDa) and SE35 (35 kDa) (Kuboyama et al 1997). In the pr esent study, we determined each N-terminal amino acid sequence. The N-termi nal amino acid sequence of SE32 was identical to that of PPAL, a stigma spe cific protein which was similar to grass pollen allergens and beta -expansi n. However, no sequences identical to the N-terminal amino acid sequence of SE35 were found in the protein databases. An antiserum raised against SE32 was found to react with both SE32 and SE35 in SDS-gel blot analysis. SE32 was detected only in the stigma, while SE35 in both the stigma and the styl e. These two proteins were not detected in other floral or vegetative organ s. Immunohistochemical analysis showed that the antigens of the anti-SE32 a ntiserum were localized in the extracellular space of transmitting tissue. Accumulation of SE32 started in the completely elongated bud and increased with flower maturation. However, accumulation of SE35 was already detected in the young bud. The antigenicity of SE35 to anti-SE32 antiserum showed st ructural similarity between SE32 and SE35, and SE35 might belong to the sam e protein family as SE32. SE32 and SE35 might soften transmitting tissue of the stigma and style, and they might play a role in the elongation of the transmitting-tissue cells or the penetration of the pollen tube into the ti ssue.