The attached picture is from a recovering lorapetalum bush in our front yard that is coming back after the Texas Deep Freeze last February. I am fascinated by the leaf on this plant that is half anthocyanin and half chlorophyll. It's almost exactly half and half. Can anyone explain the physiology of why a leaf would convert its metabolism in exactly two halves of the leaf? I would expect this process to be splotchy like the other leaf in the picture and also to take place unevenly.

I don't think it is quite that simple that anthocyanin is present versus chlorophyll that isn't. I think that the anthocyanin might be dominating over the chlorophyll and the burgundy color comes through. But in your case the reverse might be happening with green dominating purple.

As to why? I have no idea. The plant looks great and if it is healthy and growing well, I might be tempted to call it an 'oddity of nature' and forget about it. It just doesn't appear to me to be serious to cause concern.

That's technically a sectorial chimera.

The reason this happens is you have two genetically different cells in the apical meristem, with each contribuiting daughter cells for one half of the leaf. Apical meristem is the growth tissue found at the tip of the roots or, as in this case new shoots and daughter cells are exact clones of the original cell.
As for the molecular mechanisms underlying a red leaf (technically it's called a stable leaf phenotype), that's usually due to high activity levels of activity involved in the flavonoid-anthocyanin synthesis pathways through all leaf development stages to maintain a steady flow of anthocyanins. Forgive me if I do not use 100% correct terms but I studied this stuff what feels like a couple centuries ago.

What happened is one of those two cells of above was a mutant, or to be more specific it was a mutant of a mutant, expressing low levels of activity in the aforementioned synthesis pathways, hence allowing one half of the leaf to look green.

As per why it happened, absolutely no clue.

ElPolloDiablo, perfect! Just what I was looking for, although I'll need to brush up on terminology. That makes sense, having each half of the leaf arising from two daughter cells (I think that's what you said).

But the plot thickens. Now there is an entire stem (leaf?) with leaflets that have this characteristic. It's the only one on the plant. So, the genetic change occurs apparently in each leaflet. ?? That is, how did each leaflet daughter cell inherit the same mutation?? Is it the leaf (stem) itself that carries the daughter cells, and if so, why did my other example have only a single leaflet that inherited the mutation??? Strange.

Not to complicate the answer but maybe something like this:

https://www.ncbi.nlm.nih.gov/p...

Thanks Daisyl. The referenced article discusses the metabolic development of the color change in the cabbage in question. That is certainly an interesting paper, although the detail is a bit out of my wheelhouse of understanding.

What I guess I am curious about is how the leaflets develop from the main leaf stem of my lorapedalum. ElPolloDiablo suggests, if I understand correctly, that each leaflet arises from two daughter cells, each cell developing the tissue of 1/2 of the leaftlet. Hence, any mutation in a daughter cell will result in the observed difference ... color, in this case ... between the leaf halves. But, then I found an entire leaf (stem) with all the leaflets sharing the same mutation (pic above). Does this mean the two leaflet daughter cells in each leaflet share a common origin and arise in the leaf stem? Sorry if my terminology is incorrect. The conundrum is on one leaf (stem) there are only a couple of the leaflets that seem to share this mutation. On the other picture above, every leaflet appears to share the same mutation. That's confusing to me.

What ElPollo was talking about is a chimera - when two or more genetically distinct cell sets meet in one plant. The easiest to undertand are plants with variegated leaves but grafted plants are also chimera. But, the second cell set can't be invented, it had to be in the plant genetics to begin with. There are variegated Loropetalums. Is yours possibly variegated but the variegation has been "lost" (DNA is never lost, just misplaced within the plant)?

What I suggested is anthocyanin degradation, usually caused by environmental stresses. For some reason, the red in the leaves degrades and allows the green to show through. Red leaves in too much shade will lose anthocyanin but not usually in a pattern. That's what made the kale article interesting.

The chlorophyll is obviously there but masked by the anthocyanin, otherwise your plant would not be alive. So where did the anthocyanin go? Maybe your plant is a closet chimera or maybe environmental stresses caused the anthocyanin to degrade in interesting patterns.

Or it could be a hickup and the plant will never do this again.

That is yet another expression of sectorial chimerism.

Remember there are three kinds of chimerism: periclinal, mericlinal and sectorial. Without entering in the details, periclinal chimeras are the only (relatively) stable ones and the source of many mutations commonly seen in ornamental plants.
Mericlinal and sectorial chimeras are by contrast very unstable, especially considering plant cells propagate much faster than we give them credit for, especially during the Summer.
For example breeders have been trying to obtain various patterns of green/white evergreens for many years now but, unfortunately, so far only sectorial chimeras have been produced, meaning with time one genotype will outcompete the other and branches will become wholly green or wholly white.

That is exactly the fate that await those leaves, unless of course cold weather intervenes first and leaves are naturally dropped. It will be interesting to see what happens next year...

Thanks to you both. Daisyl, as I mentioned, I live in north central TX and back in Feb. we had a brutal freeze down to 0 deg. F for a day or more with several days in the teens. It was an Arctic outbreak that is very unusual here. All the glossy-leaf privet and the Indian hawthorns, popular with many here, are dead to the ground if not gone totally. Many trees didn't make it, and many that did suffered many dead branches.

The lorapedalums lost ALL leaves and I thought they were gone, but slowly red shoots started showing. I am sure what I am seeing is some mutation or some other result of the severe cold that did indeed kill many branches on the lorepedalum plants. However, that said, they are now slowly recovering. Then, on this one plant I started noticing these anomalies and just got curious about what was going on. Yes, an opportunity to add to my knowledge of plant physiology!

I'm glad you posted the question.

Hi @Ernie_n_TX,
Edit - Prescript: While I was single finger typing this, Daisyl and ElPolloDiablo and Ernie posted 😄. I'm not going to change it for now because my questions still stand.
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This is striking and fascinating! The next question is whether that pattern will continue in branches arising in the axils of these leaves.

Can you propagate Loropetalum from cuttings? If this proves to be stable you might have a fascinating new cultivar!

I think this may be a mericlinal chimera rather than sectoral because of the uniform way it is appearing from leaf to leaf on each side. Given the planarity of the leaf arrangement on the stem, I can picture the mutated area of the apical meristem rotating in a coordinated pattern.

What color is the tissue inside the leaf in the colored sections versus the green ones? What color is the reverse side of a colored leaf?

@ElPolloDiablo is likely correct that this is a mutation of the anthocyanin pathway, this produces most of the red and purple colors. Often in plant structures the colored cells are limited to the epidermis, which is a single layer on the surface in most plants.

I am not sure what is happening with your plant, that's why I'm asking for more observations.

You can read more about the technicalities of chimeras here:
https://aggie-horticulture.tam...

Pat

Pat, you raise interesting questions. Let me try and answer your questions one at a time.

- reverse side of the leaf seems to be mostly green under the miccroscope, or there seems to be a layer of green cells on the back of the leaf. I will include a photo of the back of the leaf. I have a low power microscope and under the microsope the underside looks gray-green with a layer of primarily green cells.
- Only a few leaves show this apparent chimeric appearance (by leaves I am including an entire stem with the leaflets). Other leaves on the same plant are all red and show no sign of the bicolor. Thus, I don't think this is the beginning of a new cultivar.
- under the low power microscope I am led to think the anthocyanin is breaking down in parts of the leaf, leaving the green chlorophyll, but that's just my impression. I don't have enough power to look at the cells in any detail.
- I believe you statement about the upper epidermis containing the anthocyanin is correct, given my observations of the leaf samples
- I am close to the AgriLife facility on Coit Road in Dallas. I don't suppose you have any contacts there I could compare notes with?
- Finally, it seems on these affected leaflets the anthocyanin is disappearing and leaving the green chlorophyll as a function of time. I till try and document this.


Back of two leaflets, with the front/top of one leaflet under my thumb for comparison. Under incident light (not transmitted) with the microsope the backs of the leaflets seem uniform gray-green.

Ernie_n_TX said:
- Finally, it seems on these affected leaflets the anthocyanin is disappearing and leaving the green chlorophyll as a function of time. I till try and document this.

Playing Devil's Advocate... Chimera is a permanent color change (in that leaf) and would also be present on the back of the leaf - its genetics. Anthocyanin degradation would change with age and wouldn't be consistent from back to front - its chemistry.

Daisy, I jumped the gun by saying the anthocyanin was disappearing. It will take some days of observation to make that determination. As for back and front, my microscope is not good enough but the cells covering the back of the leaflet even in the frontal red areas are a uniform gray green when directly lighted. As my photo shows, the back of the red area of the leaflet is muted by the gray-green color and when directly lighted looks quite green. ???

I still think this has something to do with the freeze, but what is going on in the leaf's biochemistry is another question. Will post temporal changes in coming days.

I'm not trying to convince you of any particular answer but I will continue to challenge conclusions when I see a potential flaw in thinking. Keep at it. Don't let anyone tell you with certainty what it is. None of us are professional geneticists or organic chemists. I'm not sure any of us even know what we are talking about. The blind leading the blind.

But it is a good discussion and I think we are all learning from it.

Hi @Ernie_N_TX,

Thank you for your careful observations! I apologize for not replying sooner, I've been treating a cold.

I am going to make short posts bc this site keeps reloading and losing what I write.

Pat

Ernie, Loropetalum is not grown here so I wanted to know whether the epidermis was green or red on the reverse side of the 2 halves.

From your picture and description it appears the epidermis might be colorless on both sides [edit: by both sides I meant both halves, the red and the green, on the underside of the leaf]. In any case, the main difference is half the upper side of each leaf. So I'll stick with that as the most relevant information.

Pat

Pat

I can see that the upper epidermis of the eventually green half is rosier on the younger leaves. Indicating that some level (quantity) of anthocyanin is present in the epidermis there. I do not know whether those anthocyanins are degrading as the leaf expands or simply being diluted as the pigment is spread thinner among the daughter cells.

Also I see some speckles of red on the green halves so it is not being uniformly degraded or redistributed as the case may be.

Pat
Edited to correct a misspelled word.

Actually the exact process that's occurring was not as interesting to me as the question of whether this chimera can be stably propagated.

That will eventually be clear whenever this branch begins to develop side branches. If the side branches also develop with leaves 1/2 green and 1/2 red then it could be stably propagated.

You would then have a new cultivar which you could name 'Harlequin' or some such. Many cultivars, especially of variegated varieties, arose as branch sports just like this.

I suspect though that the branches from one side will be all green and from the other side all red.

Only time will tell. Or if you are curious you could cut off the tip few inches and root this cutting to keep the main "harlequin" stem going. The portion left behind with a few of the half & half leaves will then begin to develop side shoots.

Genetics and physiology of this - I'll address that later. I need to rest.

Pat

Just to point in the direction that will take, I will note that if you read the beginning of the link I posted (reposted below), a chimera is by definition a genetic difference between two adjacent tissues.

If there was no genetic difference, the leaves would have continued to be solid red.

There is no physiological explanation that could cause half of each leaf to differ in color without a genetic difference.

Dr. Lineberger, who wrote the chimera article, was my advisor for my PhD research & dissertation at Ohio State. I studied general chemistry, organic chemistry, and biochemistry through the graduate level. I took every plant physiology class taught at the undergraduate and graduate levels at 3 universities. I also studied developmental plant anatomy in addition to developmental plant physiology. And a lot more related plant and science courses.

Not everybody is among the blind leading the blind.

https://aggie-horticulture.tam...

Pat