Abstract: “The reasons of dormancy, methods of breaking dormancy, and the effect of environment factors on dormancy and germination of Rosa seeds were analyzed. There were some reasons caused Rosa seeds dormancy, such as the restriction of pericarp and testa, physiol. dormancy in embryo and inhibitory substances in pericarp, testa and embryo. Therefore, breaking dormancy methods in some Rosa plants were also reviewed, including derestriction and removing inhibitory substances, etc. The environment factors, such as temp., water and light had important effects on seed dormancy and germination during development and ripening stages. Otherwise, microbial action and the time of hip collection affected seed dormancy and germination of Rosa plants. The dormancy mechanism of Rosa seeds was complex, and had great differences among various Rosa species.”
inbuilt dormancy? at times, and under some conditions. See my review of Stewart and Semeniuk’s works, in the resources of the RHA, homepage. articles.
The Chinese have published several very good articles recently, using a classification scheme for dormancy developed for many other species by some seed physiologists.
Those couple Articles from PRC, published in English have also been reviewed. The synopses have appeared, or will appear, in RHA newsletter.
Is it possble that a percentage of the embryos in jar culture that appear normal at the start of the culture but just fail to ever do any growing (unlike their peers in the jar) are in a state of some sort of embryo-induced dormancy??
Absolutely. the alternative is “dead”. Most evidence is that the inhibitors of germ. are in the testa, but one study suggested that the testa is actually needed to overcome some kind of dormancy, which may have been induced earlier by that same testa. Roughly speaking it seems that ratios of GA to ABA control sprouting but careful studies have shown that’s not all there is to it because the ABA may drop even before germ. begins, or not drop all that much yet germ. does begin. I think that was Tillberg’s work.
In arabidopsis there are specific genes for vernalization. Rick Amasino at U of Wisconsin has a bunch of publications on that. He will be an honored speaker at our university next November. Meantime you can find lots on his website. Cold affects things, daylength affects things, warmth followed by cold followed by warmth, with different daylengths affects things. Each does so in its own way.
Larry, your comments are good ones and point to a need to do some experiments along these lines with embryo culture. However, while for normal stratification the testa may be involved in breaking dormancy, in my experience the removal of the testa and immersion in dilute peroxide is usually sufficient to break dormancy.
the alternative is “dead”
Embryos which fail to germinate nearly always succumb immediately to microbial degradation indicating that they are, indeed, dead.
The reference below give a model (figure 8) for dormancy control first published by Cadman et al which may be similar to the one you were thinking about. The critical features of dormancy breaking in that model are that ABA sensitivity and synthesis decline while GA sensitivity and synthesis increase.
AFAIK experiments done with GA on intact rose seeds have not shown any affect on germination except, iirc, a negative one. On the other hand, Dr. Kuska has clearly shown that light, especially red light, promotes germination and my own experience with embryo culture supports that.
Ref: Finch-Savage and Leubner-Metzger, Seed dormancy and the control of germination, New Phytologist (2006) 171:501-523.
Yes, I am starting to see after so many embryo culture runs, that there is SOMETHING in some embryos that makes SOME OF THEM behave in some sort of “suspended animation”.
Some of these embryos are every bit alive…they will do things like develop green cotyledons but never grow roots. Others have the “alive” pearly sheen appearance, and even start to just open cotyledons, then stop in their tracks, and remain as “pearly whites frozen in time”.
I speculated recently that light in the jar may be triggering this reaction, however the same thing has occurred when some embryos are directly buried in seed raising mix (very minimal light exposure).
Maybe this observed behaviour could be related to an embryo-induced chemical inhibition to germination…that is, these particular embryos are simply “not ready” for germination at the time we chose to extract them and culture them (even though they are from ripened hips and their sibblings do grow in culture)…They could represent the “late germinations” that are observed naturally.
Perhaps this is a safety mechanism built in by nature to maximise survival of new generations…So these would germinate in the ground, presumably as the late germinators, but they stand NO CHANCE if in a culture situation as embryos, due to the long time delay factor…just speculation.
George, I’m sure you’d on the right track. The works of Zhou and Bao that I read, and probably what Henry cited above, are heavily influenced by the work of the Baskins. I have not read much of their work. A book in 1998 was titled "Seeds, ecology, biogeography and evolution of dormancy and germination (Academic Press). A relevant article is by C.C. Baskin and J.M. Baskin and titled A classification system for seed dormancy. It appeared in Seed Science Research 14:1-16 in 2004.
People have selected agronomic crops to reduce most kinds of dormancy for practical reasons. We want to have 100 % germination when we plant, and with wheat for instance, that is within 3 months from harvest. Perhaps the same has been done for roses under the intense selection used by commercial breeders. Also the tropical kinds may not have much dormancy.