Expression of a polygalacturonase enzyme in germinating pollen of Brassica napus

Abstract

Penetration of pollen tubes through stigmatic tissues in Brassica napus L. may involve the release of cell wall modifying enzymes from the pollen tube tip. We have examined the expression of a pectin-degrading polygalacturonase (PG) enzyme in unpollinated and early and late pollinated stigmas via immunoblotting and immuno light microscopy using a PG polyclonal antibody. Immunoblotting analysis indicated that PG enzyme was present at low levels in unpollinated stigmas and at high levels in pollinated stigmas. The level of PG did not detectably increase between early and late pollinated stigmas. Immuno light microscopy demonstrated that PG enzyme was present in ungerminated pollen grains, stigmatic papillae and in the tip of pollen tubes growing into the papillar wall. This latter evidence suggests that PG enzyme may play an important role in papillar cell wall penetration during pollination although other interpretations of the role of pollen PG should not be discounted.

Pistil Factors Controlling Pollination

“…Tube growth seems to be facilitated by wall-degrading enzymes produced either by the pollen itself or by the stigma. This is in agreement with the finding that group I allergens of grass pollen have expansin activity (Cosgrove et al, 1997) and that a polygalacturonase was localized in Brassica germinating pollen (Dearnaley and Daggard, 2001, and references therein). In tobacco, a species with a wet stigma and a solid style, pollen tubes grow through the intercellular spaces between the cells of the secretory zone, within the exudate produced by these cells.…”

PECTIN METHYLESTERASE48 Is Involved in Arabidopsis Pollen Grain Germination

“…A semiquantitative RT-PCR analysis investigating 66 among the 69 genes coding for PGases showed that 32 genes were strongly expressed in flower tissues (Kim et al, 2006). Other studies also have shown that PGases were present in ungerminated pollen grains of Brassica napus (Dearnaley and Daggard, 2001) and during hydration of Platanus acerifolia pollen grains (Suárez-Cervera et al, 2005). In addition, in Brassica campestris, alteration of the expression of B. campestris MALE FERTILITY2 (coding for a putative PGase) resulted in an overdeveloped intine and abnormal germination (Huang et al, 2009).…”

Pollen and Stigma Structure and Function: The Role of Diversity in Pollination

“…Hydrolysis of pectin in the stigma cell wall also is necessary, for which pollen expresses genes encoding pectin esterase and pectate lyase (Kim et al, 1996;Wu et al, 1996). A pollen-specific Brassica polygalacturonase also has been detected at the tip of pollen tubes as they enter the stigma papillar cell walls (Dearnaley and Daggard, 2001).…”