When doing flow cytometry on seed of closely related diploid and tetraploid deciduous azalea species, the ratio of the flow cytometry scores of embryo / endosperm is 2/3 for the tetraploid species but often deviates from 2/3 for the diploid species. In all cases the deviation for diploids is due to more contribution by the female than the male. Instead of equal contribution by the parents of .8 to .8 for an embryo score of 1.6 we are seeing contributions of .9 for the female and .7 for the male in diploids. Tetraploids show equal contribution to the embryo by both parents.
To illustrate what we are seeing in the diploid deciduous azalea species a typical seed has a embryo score of 1.6 and an endosperm of 2.5 indicating a female contribution of .9 and male contribution of .7. To date flow cytometry for seed for all other diploid Rhododendron species have resulted in equal contribution by the female and male parent. In general diploid deciduous azalea have a higher flow cytometry scores than other Rhododendron species. Moreover diploid deciduous azalea species are often found in contact zones with closely related tetraploid species. These contact zones normally contain triploids and physical characteristics suggest bidirectional introgression between the diploid and tetraploid species does occur.
We speculate that what might be happening is the seed formation for these diploid deciduous azaleas species is not a passive process but instead some contribution from both parents is being lost during embryo formation than is not being lost during endosperm formation. However we are not aware of mechanisms that could cause such lost during seed formation.
Hello John:
Although I do not completely understand your question and your own response, I get the general gist. You may want to look into the work of Brian Husband on Chamerion (Chamaenerion, Epilobium (Onagraceae)) or contact him at the U of Guelph (Ontario). He may have also done work on nuclear/chromosomal/genetic influences in pollen sizes, and ? seed/embryo/endosperm issues in other plants. I wonder if the differences you are seeing in diploid, triploid and tetraploid forms have relevance to the strange meiotic processes in Rosa canina (pollen vs. ovule chromosome numbers).
Best wishes,
Peter
Peter
Since the flow cytometry of seed gives two peaks one for the embryo and one for the endosperm one can calculate the contributions from the 2 parents.
In general,
female contribution = GS score endosperm - GS score embryo
and
male contribution = GS score embryo - female contribution
Initially for diploid deciduous azaleas we leaned towards towards there being an imbalance in parent contributions due to meiosis issues such as with dog roses but now we lean towards this happening due to small lose due to "mitosis" during seed formation. We believe that diploid deciduous azaleas are relatively new species that are still stabilizing after interaction with tetraploid species.
The first thing I could think of is the diploid species is exactly a hybrid, so the homologous pairing during meiosis may not be as good as it in the tetraploid status.
The first thing I could think of is the diploid species is exactly a hybrid, so the homologous pairing during meiosis may not be as good as it in the tetraploid status.
The first thing I could think of is the diploid species is exactly a hybrid, so the homologous pairing during meiosis may not be as good as it in the tetraploid status.
Chung-Ju
We speculate the less stable meiosis for diploids may be due to introgression from the tetraploids by the way of a triploid pathway. Diploid and tetraploid east coast deciduous azaleas are often in contact zones. These contact zones often contain triploids some of which are fertile. Both the diploids and tetraploids show visual signs of bidirectional introgression in such contact zones.
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