Articles
BIOCHEMICAL MARKERS OF COMPATIBILITY IN APPLE
Biochemical studies have evinced the role of peroxidases (PER) as indirect regulators of incompatibility reactions and molecular investigations have indicated that RNAses are the real gametophytic stylar product of the S locus (Anderson et al., 1986; Kaufmann et al., 1991; Kirch et al, 1989, 1995; McClure et al., 1989, 1990; Sassa et al., 1992; Thompson et al., 1991; Thompson and Kirch, 1992).
The present study reports a biochemical approach to identify markers of incompatibility in apple, another gametophytic self-incompatible species.
Variations of 6 isozyme systems (PER, PGI, ADH, MDH, AcPH, PGM) were detected in whole pistils and separated stigmas and styles of cv.
Golden Delicious self-pollinated (incompatible reaction SP) and cross-pollinated with Red Delicious pollen (compatible reaction CP); the tests were assayed 24, 48 and 96 h after pollen deposition on stigmas.
Only PER and PGI seemed to have a dynamic role in the pollen-style interaction.
PER showed a supplementary band in CP stigmas of flowers close to anthesis, which disappeared 24 h after pollination; the same band was detected also in SP stigmas of flowers at the pink-bud stage.
A supplementary band was detected even in PGI gels and always found in SP and CP stigmas.
Therefore, only PER worked as a specific marker of self-incompatibility in Golden Delicious flowers close to anthesis; PGI failed to discriminate cross- from self-pollinated flowers.
The other isozymes either detected the presence of pollen on stigma surface (ADH, MDH) or did not evince any significant variation (AcPH, PGM). The important role of PER in self-incompatibility reactions in Golden Delicious confirms the known similarities between the self-incompatibility systems of Solanaceae and Rosaceae and suggests that investigations be extended to other apple genotypes.