JXB Advance Access originally published online on May 23, 2006
Journal of Experimental Botany 2006 57(9):2001-2013; doi:10.1093/jxb/erj147
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RESEARCH PAPER |
Style-by-style analysis of two sporadic self-compatible Solanum chacoense lines supports a primary role for S-RNases in determining pollen rejection thresholds
IRBV, Biology Department, University of Montreal, 4101 rue Sherbrooke est, Montreal, Canada H1X 2B2
*To whom correspondence should be addressed. E-mail: mario.cappadocia{at}umontreal.ca
A method for the quantification of S-RNase levels in single styles of self-incompatible Solanum chacoense was developed and applied toward an experimental determination of the S-RNase threshold required for pollen rejection. It was found that, when single style values are averaged, accumulated levels of the S11- and S12-RNases can differ up to 10-fold within a genotype, while accumulated levels of the S12-RNase can differ by over 3-fold when different genotypes are compared. Surprisingly, the amount of S12-RNase accumulated in different styles of the same plant can differ by over 20-fold. A low level of 160 ng S-RNase in individual styles of fully incompatible plants, and a high value of 68 ng in a sporadic self-compatible (SSC) line during a bout of complete compatibility was measured, suggesting that these values bracket the threshold level of S-RNase needed for pollen rejection. Remarkably, correlations of S-RNase values to average fruit sets in different plant lines displaying sporadic self-compatibility (SSC) to different extents as well as to fruit set in immature flowers, are all consistent with a threshold value of 80 ng S12-RNase. Taken together, these results suggest that S-RNase levels alone are the principal determinant of the incompatibility phenotype. Interestingly, while the S-RNase threshold required for rejection of S12-pollen from a given genetic background is the same in styles of different genetic backgrounds, it is different when pollen donors of different genetic backgrounds are used. These results reveal a previously unsuspected level of complexity in the incompatibility reaction.
Key words: Gametophytic self-incompatibility, single style analysis, S-RNase, Solanum chacoense, threshold
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