Pollen tube, penetration

MicroPYLE The minute orifice in the integuments of an ovule through which the pollen tube penetrates to the embryo sac in paragamic plants. 

In addition, a new class of proteins (a-expansins) has been discovered in plants that appear to disrupt the interactions between cellulose chains, without hydrolytic activity, to allow cell wall expansion [18]. A different, but related, set of molecules (P-expansins) has been found in pollen [19]. These molecules appear to help the growing pollen tube penetrate through the cell walls in the ovule allowing fertihzation. There is prehminary evidence that the addition of expansin to cellulases stimulates crystalhne cellulose hydrolysis [20]. 

Heslop-Harrison, J. and Heslop-Harrison, Y. (1981) The pollen-stigma interaction in the grasses. 2. Pollen-tube penetration and the stigma response in Secale. Acta Bot. Neerl., 30, 289-307. 

The pollen tube walls contain callose-like polysaccharides that absorb aniline blue. That is why this method is very useful to detect pollen tube elongation and to understand how the tube penetrates the inside of the pistil tissue. The pollen tubes grow from the surface ofthe stigma through... 

Another problem is the direction of pollen tube growth, which should be considered as tropism, related to attraction by the fertile ovules. Many observations of pollen tubes in the fluorescence microscope supported this suggestion—pollen tubes pass by the sterile ovules and grow in the direction of the fertile ones. The number of ovules penetrated by a pollen tube is correlated with the number of developing seeds, which supports the hypothesis about interaction (attraction) between the ovule and pollen tube (1,2,5). 

Unilateral incompatibility is a phenomenon in which self-compatible species can be crossed as a female, but not as a male, to self-incompatible species (Abdalla and Hermsen, 1972). Pollen tubes fail to penetrate stylar tissue in self-incompatible (female) X self-compatible (male) crosses. Although most diploid Solarium species are self-incompatible, the Mexican species S. verrucosum is self-compatible. Dinu et al. (2005) found that S. verrucosum could be crossed as a female, but not as a male, to self-incompatible species. It is sometimes possible to find exceptional plants that do not exhibit unilateral incompatibility in self-incompatible X selfcompatible interspecific crosses (Pandey, 1962). The identification of such plants allows a breeder to overcome the unilateral incompatibility crossing barrier. For example, exceptional plants ( acceptors ) that accept S. verrucosum pollen and produce fertile hybrids have been reported (Eijlander et al., 2000). It is interesting that some acceptor plants will accept pollen... 

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