apomictic?

From: Mary Jane Hatfield <oneota at ames.net> on 1999.02.22 at 03:43:19(3051) Concerning my Dracontium spruceanum inflorescence, it was suggested that it might be setting seed. I wondered how that might be possible since I only have the one plant with the one flower (which has been flowering for over a month now) I was told *Look up "apomictic"* which I did. I found ... +More reproduction involving the specialized generative tissues but not dependent on fertilization Aroid-L archives refer to the term but do not explain it. Maybe it is something everybody (but me) already knows. http://gnome.agrenv.mcgill.ca/breeding/apomixis.htm Please, tell me more. Do all plants do this sometimes? Why sometimes and not other times? Now I am curious. Thanks. MJ Hatfield

From: dave-poole at ilsham.demon.co.uk on 1999.02.22 at 16:42:15(3055) In apomictic seed bearers, several embryos are formed within the seed (polyembryony). One is the result of sexual reproduction and will have shared genes from both parent plants, the remainder will have been produced asexually and be clones of the mother plant. This is most commonly demonstrated in several Citrus species - the clonal seedlings being noticeable more vigorous and easily identified. When apomictic germination occurs, it is a useful means of reproducing the mother plant without having to worry about hybrid variation. David Poole

From: Sue Zunino <suez at northcoast.com> on 1999.02.22 at 22:14:28(3056) David, Could you explain this a bit further? >One is the result of sexual reproduction and will have shared genes from both parent plants,< Apomixis is any form of asexual reproduction. When did sexual reproduction occur for one of the embryos to have genes shared by both parent plants? Is this carried in the genes of the apomictic plant so that pollination is no longer necessary? Sue Zunino

From: dave-poole at ilsham.demon.co.uk on 1999.02.23 at 15:55:27(3057) >Could you explain this a bit further? >Apomixis is any form of asexual reproduction. When did sexual >reproduction occur for one of the embryos to have genes shared by both >parent plants? +More Not strictly true. Apomixis is the normally the reproduction from an unfertilised egg cell or the somatic (nucellar in part) cells associated with the egg cell. Asexual reproduction occurs in many ways in plants - adventitious budding etc., but that is not apomixis. In certain species, seeds are formed as a result of normal sexual reproduction, but these can be polyembryonic. Only one embryo will be the result of fertilisation of the flower and this can exhibit uncertain characteristics as a result of hybrid variation caused by two sets of genes coming into play. The remaining two, three or four embryos will be 'nucellar' or apogamic seedlings, vegetatively formed from the nucellus of the seed. They are identical to the mother plant and are true clones. In this way, it is perfectly possibly to get a true cultivar of a dessert orange for instance, from seed by selecting out and retaining the nucellar seedlings. The difference in appearance is invariably quite marked and 'normal' seedling can be easily identified since it is usually considerably less vigorous. These apomictic embryos are as it were, adventitious buds formed on the nucellus in a similar way to the adventitious buds produced on the leaves of certain Kalanchoe (Bryophyllum) species and the rachis of Polystichum ferns etc. Pollination of the flowers has to take place in order for the seed to form in the first place. Fruits can be formed parthenocarpically (without pollination), but no fully formed, true seeds are present. > Is this carried in the genes of the apomictic plant so >that pollination is no longer necessary? No, pollination is necessary for seed formation, subsequent apomixis where it occurs, follows on as described above. Apomixis has been demonstrated in many plants where the ovary has been cultured in vitro and can be initiated from somatic and embryonic sac cells. When apomixis occurs naturally, it is most frequently the result of embryogenesis from the nucellus. David Poole

From: Lewandjim at aol.com on 1999.02.23 at 16:22:06(3059) As I suspected this discussion of apomictic reproduction may get complicated. Like Sue Zununo, I was a little confused by David Poole's definition and example. Perhaps there are degrees of apomixis. The most familiar example that I know involves Hosta venticosa which I believe ONLY produces clones of itself regardless of what the pollen parent might be. I offer this only as further information, not as a definitive answer. Jim Langhammer

From: Neil Carroll <zzamia at hargray.com> on 1999.02.23 at 16:32:55(3060) Sue, I will try to answer this question about "apomictic" the way I have always understood it. Daves answer would have left me with some questions also. +More from the Greek 'apo' away from, out of, asunder, free from the greek 'mixis' to mix. so ... free from mixing The American College Dictionary says..Reproduction without meiosis or formation of gametes. IN other words, plants that form seed without sexual union. >>One is the result of sexual reproduction and will have shared genes from both parent plants, The statement that "one is the result of sexual reproduction" does not jibe with my understanding of apomixis. Some examples of Anthurium with this trait are: Anth. gracile, punctatum, and scandens. As pointed out by Mike Madison, these anthuriums are often found in assosiation with ant gardens and he feels that there may be some association with apomixis and these gardens. Possibly the ants would keep pollinators away and the plants needed another way to form seed. > >Apomixis is any form of asexual reproduction. >Sue Zunino Apomixis is NOT any form of asexual reproduction. Apomixis is asexual reproduction involving flower parts. Seeds without sex. other forms of asexual reproduction which are not apomixis are, cuttings, leaf propagation, tissue culture, offsets, bulbils etc. Neil Carroll

From: StellrJ at aol.com on 1999.02.23 at 19:49:39(3061) In a message dated 2/23/99 7:42:43 AM Pacific Standard Time, dave- poole@ilsham.demon.co.uk writes: > This way, it is perfectly possibly to get a true cultivar of a +More > dessert orange for instance, from seed by selecting out and retaining > the nucellar seedlings. The difference in appearance is invariably > quite marked and 'normal' seedling can be easily identified since it > is usually considerably less vigorous. If the "normal" seedling is less vigorous than the apomictic ones--and would therefore be at a competitive disadvantage to them--why does the plant produce it? Pollination/fertilization costs the plant energy, so why do it just to produce a disadvantaged seedling? Jason Hernandez Naturalist-at-Large

From: dave-poole at ilsham.demon.co.uk on 1999.02.23 at 22:46:45(3064) Neil wrote in response to Sue: >>Apomixis is NOT any form of asexual reproduction. Apomixis is asexual >>reproduction involving flower parts. Seeds without sex. > +More >other forms of asexual reproduction which are not apomixis are, = cuttings, >leaf propagation, tissue culture, offsets, bulbils etc. Very true. Also, relying upon literal translations from either the Greek or Latin is as unreliable as you can get, because these are invariably considerably distanced from the reality and are only descriptions in the broadest possible sense. Defining apomixis in plants is almost impossible without going into details at cellular level and I have tried, albeit very ponderously to give a very broad outline of what takes place in my reply to Sue Zunino. The immense problem is that the plant kingdom is so infinitely variable and for every definition, there are innumerable exceptions. The general consensus appears to be that apomixis is asexual reproduction involving (almost exclusively) those parts of the ovum not directly involved with fertilisation. Lets try to get this into perspective. Most of us are familiar with the idea of a placenta and umbilical cord in animals (including us). These are the connective tissues or 'somatic' tissues which remain part of the parent but are essential in the continued development of the embryo. Genetically they are identical to the host parent (mother) and any tissue culture taken from these, resulting in an offspring, would be clones of the mother. In plants there are vaguely similar (connective or integumental) somatic tissues and it is in these areas that 'budding' or embryo genesis can take place. I prefer the term 'apogamic' because it more accurately describes the 'non-gametal' ie. unfertilised status of these embryos. Dave Poole

From: dave-poole at ilsham.demon.co.uk on 1999.02.23 at 22:52:28(3065) Jason Hernadez wrote: >If the "normal" seedling is less vigorous than the apomictic ones--and = would >therefore be at a competitive disadvantage to them--why does the plant = +More produce >it? Pollination/fertilization costs the plant energy, so why do it just= to >produce a disadvantaged seedling? This is the thousand dollar question and the whole issue is so complex that it is almost impossible to define and describe succinctly. Apomixis is probably a second line means by which reproduction can take place. Why the product of true fertilisation of the ovum is frequently less vigorous at the outset remains unanswered. The simple fact is that it does in Citrus species at the very least. Why is anybody's guess. Any 'hybrid' is more likely to be disadvantaged compared to the true species in any case - just look at the odds of finding a 'better-than-the-parent-plant' from any batch of hybrids. The ideal is that similar species should reproduce with each other. However, plants being as diverse and as exploitative as they are, have innumerable means by which they can ensure their survival. Apomixis is only one of many methods by which at the very least, some of the genes can be passed on in some species. It is far from perfect, but at least it is reproduction. David Poole

From: Sue Zunino <suez at northcoast.com> on 1999.02.24 at 19:23:24(3066) What was my original question? Thank you all for the great lessons on asexual fertilization. After being prompted by the wonderful and complex explainations, I mixed a bit of searching in with them and found that (if I have this right) my little Anthurium trinerve's genes (for which I asked the question in the first place because it's seeds are fertile and there is not another plant, and providing it is apomictic) has a complete set of chromozomes within the seed embryo making it possible to reproduce, by cloning itself, without needing another plant. I know this is a very weak explaination. Ok, I don't get this completely, but I'm thinking. Apomixis is ONE form of asexual reproduction. There are many types of apomixis such as recurrent, nonrecurrent, adventitious, vegetative, and polyembryony. But is Anthurium triverve a facultative apomict? Yes or no. Thank you Dave, Don, Ray, Neil, Jim, and Jason for your explainations, and MJ for asking the original question, Sue Z. +More PS: If I should ever get to meet any of you, DON'T bring this subject up. I don't really get it.

From: "Toby Marsden" <tobym at beer.com> on 1999.02.24 at 19:54:14(3067) Jason et al, >If the "normal" seedling is less vigorous than the apomictic ones--and would >therefore be at a competitive disadvantage to them--why does the plant produce >it? Pollination/fertilization costs the plant energy, so why do it just to >produce a disadvantaged seedling? Unless I have missed something large indeed (not unlikely), this question is akin to asking "Why do plants reproduce sexually when they can produce more vigorous offspring by reproducing vegetatively (asexually)?", being as the fertilised seedling is a product of sexual reproduction, while the unfertilised or apomictic seedling is a product of asexual reproduction. The answer to this question is to do with the Evolution of Species via Natural Selection. How can a plant improve or change, if it produces offspring identical to the parents? Sorry if I am confusing the issue by taking it off at a tangent. Kindest regards, Toby +More -- Toby Marsden, Herefordshire, UK.

From: mplewinska at mindspring.com (Magdalena Cano Plewinska) on 1999.02.25 at 02:54:55(3070) On Tue, 23 Feb 1999 13:48:34 -0600, StellrJ@aol.com wrote: >If the "normal" seedling is less vigorous than the apomictic ones--and would >therefore be at a competitive disadvantage to them--why does the plant produce >it? Maybe sometimes it's a better plant (for the environment) and maybe the plant produces lots of them "hoping" for that one superior one in the lot. As I understand it, apomixis tends to happen in plants that are optimally adapted to their environment, so they just produce lots of clones of themselves on the principle that "you shouldn't argue with success." But if conditions should change, these clones may not be so well adapted, so it's a good idea to play it safe and make a few plants that are different and may do better in the new environment. -- Magda Plewinska mplewinska@mindspring.com +More Miami, FL, USA

From: mplewinska at mindspring.com (Magdalena Cano Plewinska) on 1999.02.25 at 02:59:50(3071) On Tue, 23 Feb 1999 16:45:43 -0600, dave-poole@ilsham.demon.co.uk wrote: >relying upon literal translations from either the +More >Greek or Latin is as unreliable as you can get, because these are >invariably considerably distanced from the reality and are only >descriptions in the broadest possible sense. Ain't that the truth! >Most of us are familiar with the idea of a placenta and umbilical cord >in animals (including us). These are [...] tissues which remain part of >the parent but are >essential in the continued development of the embryo. Genetically >they are identical to the host parent (mother) and any tissue culture >taken from these, resulting in an offspring, would be clones of the >mother. Ummmm..... Don't mean to be contrary (and I'm certainly no expert on plant reproduction) but I think that the above statement shows the danger of drawing parallels between plant and animal sexual reproduction. I happen to be a human geneticist, so I know a fair amount about human sexual reproduction and embryology. I know much less about plants. So please, those of you who know, point out where I'm wrong below. This is what I gather from my limited reading about flowering plant reproduction. The basic mechanism of meiosis is the same in plants and animals (at least higher vertebrates like humans) but that's where the similarity ends. Meiosis in humans ends in one haploid cell, the gamete. These cells do not divide further. Two such cells combine to form a zygote. The zygote is a diploid cell with nuclear genes derived from both parents and mitochondrial genes, as well as most of the cytoplasm, derived from the mother. The zygote divides and its cells form the embryo (including the umbilical cord), the extra-embryonic membranes (chorion and amnion) and the placenta. These are fetal, not maternal, tissues in humans. They are diploid and are genetically identical to the fetus. In plants, meiosis ends in a haploid cell. This is where things begin to differ from animals. The haploid cell which resulted from meiosis then goes on to divide into a number of identical haploid cells. These haploid cells specialize to form reproductive structures such as pollen tubes and sperm cells in the male gametophyte and the egg, polar nuclei, antipodal cells and synergids in the female gametophyte. This division and specialization of haploid cells seems to me to be a fundamental difference in the mechanism of fertilization in plants and animals, although oddly enough, the final result of fertilization is very similar: a diploid cell (zygote) with nuclear genes derived from both parents and maternally derived plastid genes. I don't know about the origin of the cytoplasm in the plant zygote. A second difference is that plants also have a nutritive tissue, the endosperm, which is the result of a separate fertilization event and is not usually diploid, from what I gather. There is no such thing in humans. Of course, the human embryo would not get very far without the mother and her specialized reproductive structure, the uterus and its adnexa, but these are permanent structures in the mother, not ones formed anew with each reproductive cycle. Only the uterine lining is renewed every cycle. Maybe someone can explain it better than I - I'm certainly no expert in plant reproduction. But I implore you not to draw too many parallels between the process in plants and animals - we are pretty different at a fairly fundamental level. It's really amazing that so many parts of the scheme are so similar. >The general consensus appears to be that apomixis is asexual >reproduction involving (almost exclusively) those parts of the ovum >not directly involved with fertilization. Do you need fertilization to trigger this asexual reproduction or can it happen by itself? Also, do you mean "the ovule"? The ovum is the unfertilized female gamete (even in plants, according to my botanical dictionary). The ovule seems to be the reproductive structure derived from maternal tissue. -- Magda Plewinska mplewinska@mindspring.com Miami, FL, USA

From: "George R Stilwell, Jr." <grsjr at juno.com> on 1999.02.25 at 03:32:40(3073) Sue, The answer is - Maybe. Ray +More ___________________________________________________________________ You don't need to buy Internet access to use free Internet e-mail. Get completely free e-mail from Juno at http://www.juno.com/getjuno.html or call Juno at (800) 654-JUNO [654-5866]

From: Neil Carroll <zzamia at hargray.com> on 1999.02.25 at 15:13:28(3074) At 04:47 PM 2/23/99 -0600, you wrote: >Neil wrote in response to Sue: > +More >>>Apomixis is NOT any form of asexual reproduction. Apomixis is asexual >>>reproduction involving flower parts. Seeds without sex. >> >>other forms of asexual reproduction which are not apomixis are, = >cuttings, >>leaf propagation, tissue culture, offsets, bulbils etc. >Very true. Also, relying upon literal translations from either the >Greek or Latin is as unreliable as you can get, because these are >invariably considerably distanced from the reality and are only >descriptions in the broadest possible sense. That's quite a statement!! If relying on literal translations from the Greek or Latin are as unreliable as you can get, then why bother on trying to use discriptive language at all to describe organisms? I agree only that sometimes these words are far from reality. In quite a few other cases the scientific name of a plant or animal can be very discriptive and at times, the name is all you need to seperate one species from another. Of course literal translations can be a slippery slope, they are also far from being "invariably considerably distanced from reality". When giving a new name to a plant or animal a few choices are available to the taxonimist. The subject can be named after a location, it can honor a person, or the name can reflect a characteristic of the subject. While these names with their translations cannot be a totally reliable proposition, they are more useful than being "as unreliable as you can get". Neil

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