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Bigenerics and variegation

Posted by LisaCLV HI (My Page) on
Fri, Jul 1, 05 at 4:28

I recently posted some pictures of a variegated Foxtail Palm (Wodyetia bifurcata) seedling on another forum, and speculated as to the cause of the variegation. The consensus of the respondants seems to be that what I have is most likely a hybrid between Wodyetia and some species of Veitchia, as they are apparently known to cross and produce variegated offspring.

My question is: why would bigeneric hybrids be more prone to variegate? Is this a known phenomenon in any other plant families? I have made several bigeneric bromeliad hybrids with mixed success, but never had any come out variegated. This is the first I've heard of this happening.

Here is a link that might be useful: Variegated Foxtail Palm thread


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RE: Bigenerics and variegation

Variegation is not uncommon in hybrids, even interspecific, but often the variegation affects characteristics other than color. For instance, if the parents have different types of trichomes (hairs) the hybrid may display patches of both types.

Blackberry fruits cling to the core even when ripe. Raspberry "caps" slip off. Hybrids of blackberry and raspberry can vary (i.e., express variegation) even on a single plant. Some caps will come free, some will cling, and some will be part free/part attached.

Some of the early Aurelian lily hybrids seemed uncertain (or variegated) as to whether the petals should curve gently like the trumpet parent or reflex strongly like the turkscap L. henryi. The petals were held more-or-less wide spread but attractively twisted.

Your variegated palm might be explained if two conditions are true:

1) Albinism results from an interaction between nuclear genes (in the chromosomes) and genes in the chloroplasts. This has been observed in interspecific hybrids in Epilobium and in Hippeastrum.

2) Both the seed parent and the pollen parent contribute chloroplasts. This occurred in seedlings from a normal coastal redwood pollinated by an albino tree. Most of the seedlings were at least partially white (ranging from pure albino to slightly variegated). In some cases the variegated seedlings became solid green as they matured.

Tentative conclusion:
Either genes from the pollen parent induced the maternal chloroplasts to become white, or chloroplasts from the pollen are blanched by genes from the seed parent.

In either case the loss of variegation would result when the green chloroplasts come to dominate, and the white ones are lost or relegated to a tissue that doesn't show.

A green geranium (Pelargonium) pollinated by a green/white variegated chimera-type will produce seedlings with both types of chloroplast. The greens and whites can sort themselves out as the plants develop, recreating the chimerical variegation (green leaves with white margins).

I don't know how palm meristems are arranged. Maybe they cannot support a stable chimerical variegation like that of Pelargonium.

Karl King


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RE: Bigenerics and variegation

You gave me a lot to think about, Karl, and I even understand most (if not quite all) of it! :-) I had never really thought of variegation as applying to anything other than pigmentation, although I am familiar with the concept of chimeras. I've always thought of hybrids as posessing a blending of parent traits, or manifesting a dominant one, rather than being a chimerical mosaic, but I can see how that could occur, and how an albino or chimerically variegated parent on either side could cause this.

What I'm not getting is why variegation/albinism should routinely spring from any combination of genes from two normal green parents. You mentioned something about an interaction between genes in the nucleus and genes in the chloroplasts, and I'm afraid that's where you lost me. I guess I need to brush up on my genetics and cellular biology, but in the meantime, can you explain how that could trigger a color break? I don't know how palm meristems are arranged either, but I'm hoping the variegation will be stable in the adult plants too.

On a separate note, my experience with bromeliad hybridizing has been that if the seed parent is "variegated" or medio-picta (green margins with the central leaf portion white or yellow), then the offspring will come out just as if the parent had no variegation. If, however the mother plant is ALBO-MARGINATED, all the seedlings will be albino and die. Can you explain this phenomenon? There are also a handful of fairly reliable variegation-transmitter plants, but as you can imagine, getting hold of one of these is not easy, as they tend to be carefully guarded by breeders and not offered for sale. The percentage of variegated offspring from them is apparently pretty low, and it has also lead to a situation where a lot of variegated hybrids look alike because the same genetic stock is being used over and over again.

I am interested in ways to stimulate variegation (without using toxic chemicals) in a number of different plant families (gingers are another), and would welcome any input on this.


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RE: Bigenerics and variegation

Lisa,

Yes, this business gets complicated pretty quickly. Patterns of variegation may be similar but the underlying mechanisms can be very different.

The thing to note in this is that chlorophyll is not dispersed throughout the cell or tissue. It is concentrated in discrete bundles called chloroplasts.

Chloroplasts are tiny microbes with their own chromosomes and genes. They are effectively domesticated cyanobacters (formerly known as blue-green algae). They live in cells and reproduce, but much of their activity is regulated by the host nucleus. Genes in the host's chromosomes can tell the chloroplasts what to do and when to do it.

A tomato is green as it grow because the chloroplasts are filled with chlorophyll. As the fruit ripens, the chloroplasts are instructed to turn off chlorophyll production and concentrate on synthesizing carotenes -- yellow, orange or red.

The same thing can happen in flowers. Ordinarily chlorophyll synthesis is turned off, though there are many exceptions in nature and in gardens. With the chlorophyll gone, the chloroplasts can be directed to synthesize carotenes (yellow is most common, but flamingo pink irises have lycopene -- the same pigment as in scarlet tomatoes). Now the chloroplasts are called chromoplasts. Or the plastids (another name for them) can accumulate starches, oils or proteins. These are called leucoplasts.

When two species have been isolated for a long while their regulatory "languages" can become altered enough to cause some confusion in hybrids. Both species can instruct their own chloroplasts to be green in leaves and not-green in flowers, so all is well.

But when we crossbreed the species there may be a language barrier, so to speak. The genes of one species may be shouting "Be green", but the chloroplasts from the other species are hearing "Not green". In cases where chloroplasts from both parents are present, some will respond properly, others not.

Chloroplasts, being indepent little organisms, have their own habitat preferences. A mixed population (some from each parent) can become segregated if those from one species tend to migrate towards one part of the cell while those from the other parent migrate to a different part. With each cell division the sorting out proceeds a little more until the derived tissues contain only pure cultures -- some tissues contain plastids from one parent, adjacent tissues contain only those from the other parent. And where the chloroplasts are differently colored we get a separation of white (or yellow) and green.

Of course, this segregation may happen in any hybrid. But if both types of chloroplast are green we won't notice the phenomenon without special tests.

Another phenomenon worth noting is the tendency (in some plants) for the stamens to be derived from the outer layer of tissue, while the ovaries are derived from the inner layer. This is possible because most flowering plants maintain a three-layered meristem that favors periclinal chimeras. I've attached a link below to a web page that explains this organization.

Geraniums with white margins on their leaves fit this model. If we cross variegated x green, most of the offspring will have green leaves because the ovules are derived from the green inner layer of tissue. But in the reciprocal cross, green x variegated, the pollen is derived mostly from the albino layer. Thus the pollen carries mostly albino chloroplasts and many of the crossbred offspring will be variegated.

And as I discussed above, the albino and green plastids tend to migrate differently within the cells and to become segregated as the plant develops. In this case the migratory trend is for the white chloroplasts to become concentrated in the outer layer of tissue, the greens in the inner layers.

Have I confused you thoroughly?

Karl

Here is a link that might be useful: Origin, development, and propagation of chimeras


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RE: Bigenerics and variegation

Thanks for the crash course and the link, Karl. It will take me a while to digest all of this, but you haven't confused me thoroughly, just partially! The more I read it over though, the more the lightbulbs start turning on in my head, so I guess there's hope!

Now that you mention it, I do vaguely recall something from an ancient biology class about chloroplasts containing blue-green algae, but the idea that that meant you were dealing with two entirely separate DNA sequences within the same cell, or that both sequences could be passed on through the pollen simply never occured to me. So then I'm guessing that a conflict in messaging between the nuclear genes and those in the chloroplasts might in some ways be similar to what happens when a virus infects the cell, which also can result in variegation.

The part about a species being isolated increasing the chances of this kind of miscommunication would make sense with this palm scenario, since apparently the population of Wodyetia (a monotypic genus) was until pretty recently limited to a remote region in N.E. Australia. It was only within the last 15-20 years that it was "discovered" by westerners and introduced into the trade. I guess it is closely enough alligned with the Veitchias to cross with them, but there does seem to be a bit of a language barrier, which explains the mixed signals.

Since most of the plants I work with are monocots, I was interested in the way the layers of tissue are arranged differently than in dicots. I didn't realize that the leaf margins derived from a different layer than the central leaf blade, but if the ovary is derived from the same layer as the leaf margin, that would explain the complete albinism of bromeliad seedlings from albo-marginated seed parents.

Just looking at the pattern of variegation on the palm seedlings, it seems pretty likely that they are mericlinal chimeras rather than the more stable periclinal variety, although the mere fact of instability doesn't necessarily mean it won't persist into adulthood. What the link article doesn't really make clear is what factors might be more likely to trigger one type of chimera over the other. Of course, in the case of palms, even if it was stable it couldn't be propagated vegetatively anyway-- not even by tissue culture, by the sound of it.

Oh well, I guess I'll just enjoy it as long as it lasts!

-Lisa


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RE: Bigenerics and variegation

Lisa,

I have a link below to a couple of pictures I took of a small bush that can change its pattern of variegation. When it receives direct sun light it takes on the sharply defined green/white variegation. But in shade the leaves become cream colored with lots of green spots. There are intermediate stages as well.

This is particularly striking when the different patterns occur on the same plant. The bush pictured is on the north side of a building. Some of the branches receive late afternoon sun while the others only get reflected light.

It appears that the two types of chloroplasts are competing/cooperating in some way that isn't clear to me.

This example may is not quite like your variegated palm, of course. On the other hand, if you had two specimens it would be interesting to see whether one growing in full sun would be more inclined to lose its variegation than one in light shade.

There are variegated monocots that are quite stable. Iris pallida variegata is a common example, along with variegated tulbaghias, tulips, and others. Variegated clivias tend to have leaves striped white, but not in a periclinal fashion. Variegated crinums are often irregularly spotted.

Karl

Here is a link that might be useful: Shifting variegation


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RE: Bigenerics and variegation

Is this thread a little too late to revive?

I question the statement; "2) Both the seed parent and the pollen parent contribute chloroplasts." or would like to know the logic as to how pollen can pass on chloroplasts, as was under the impression that pollen cell is only a nucleus no cytoplasm??? hence pollen can be frozen and still be effective in fertilization.
Am not being critical, just have an anomaly in my mind, which blocks my ability to follow the logic? which is interesting to me.
Allan


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RE: Bigenerics and variegation

hi, i had a garden which was watered by bore water that had travelled through a area of dolomite the water was also high in cloride and large numbers of the weeds grew veriegated. i would like a veriegated rose so i will conduct some experiments with dolomite and dmso to see if i can get a veriegation. kevin


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RE: Bigenerics and variegation

this was a very interesting article since i collect variegated palms! hybrid palms that are variegated are likely due to genetics, whereas pure species that come up variegated are likely viral. is that correct?

Here is a link that might be useful: More info on variegation and variegated palms


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RE: Bigenerics and variegation

  • Posted by hendy USDA zone (My Page) on
    Fri, Feb 20, 09 at 6:37

http://nsa05.casimages.com/img/2009/02/12/090212030601936936.jpg
a little experience..


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