# Poliploid plants more heat tolerant?



## eteson (Jun 21, 2014)

A few months ago I had a disaster in my growing room and lost several Phrag flasks because the air conditioning system failed while I was traveling ... Today while I was throwing away the unrecovered flasks, I noticed that in various crosses only the flasks treated for polyploidy had surviving plants (about 20%) while in the untreated plants the survival rate was 0%. I was wondering if polyploid plants could be also more heat tolerant than normal ones.


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## TyroneGenade (Jun 21, 2014)

I would guess "yes!" and here is why.

The chemical reactions we could call decay proceed at a rate that is proportional to temperature. The rate doubles for every 10 degree C increase. Living organisms repair the damage caused by these decay reaction. When the rate of damage exceeds the rate of repair then degeneration/dying sets in. Polyploid organisms have more genes and can thus produce more proteins that can perform the repairs. The same principle occurs in cancer biology. As cancer progresses the cells become polyploid and are able to better survive stresses such as chemotherapy. So, hang onto those survivors: they may be heat tolerant and revolutionize Phrag growing.


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## NYEric (Jun 21, 2014)

Interesting.


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## PaphMadMan (Jun 22, 2014)

I agree with everything Tyrone said. The double dose of genes, and higher level of whatever those genes produce that help protect and repair tissues, is a probable factor in survival of these seedlings. In horticulture in general it is widely recognized that higher ploids often have greater frost tolerance. I see no reason why a marginal increase in heat tolerance shouldn't result also. 

Definitely watch those seedlings. They are certainly selected for stress tolerance, and probably polyploidy.


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## Lordoftheswarms (Jun 22, 2014)

That's not how cancer works, but who cares.


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## TyroneGenade (Jun 23, 2014)

Lordoftheswarms said:


> That's not how cancer works, but who cares.



I care. Read http://www.ncbi.nlm.nih.gov/pubmed/20388083 & http://www.ncbi.nlm.nih.gov/pubmed/22967442 . In the lab down the passage from me, when they gave the polyploid cancer cells caffeine it caused the cells to bypass their repair check points and the anti-cancer drugs killed a higher percentage of cells. This is slowly working its way to clinical trials (http://www.ncbi.nlm.nih.gov/pubmed/19802667 ). (The lab I am referring to did not discover this effect, they were just doing experiments with the idea.)


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## cnycharles (Jun 23, 2014)

See? One more reason to not drink coffee... (Normal cells won't repair themselves)
Just kidding, it may help 


Sent from my iPhone using Tapatalk


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## naoki (Jun 23, 2014)

Eliseo, that is an interesting observation (you can use Fisher's exact test to see if the difference is statistically significant; how many flasks did you have before the cooling failure?).

I'm a bit surprised, though. In general, the synthetic polyploids are fairly "screwed up" genomically (genomic shock) since natural plants are finely tuned machines. This genomic shock is probably less with auto-tetraploid (doubling the genome of single species, which is the case with your Pk) compared to allo-tetraploid (doubling the genome by combining two species) since genes are familiar to each other in auto, but allo- has to deal with genes they haven't seen each other before. But still, the expression levels of genes need to be compensated, so the 1st gen synthetic autotetraploid can be still screwed up. Our current knowledge suggests that this genomic shock gets adjusted fairly quickly in the first couple generations through natural selection. There are lots of fascinating research in this field.

As far as I know, there isn't a consistent pattern about whether the 1st gen synthetic polyploids become cold or heat tolerant. Generally, their fitness is lower than the diploid (at least for the 1st gen). Now, it is fairly common that the cell division is slower in tetraploids (4x). The size of 4x cells are generally bigger than 2x cells, as you know, so the slower cell division rate may not be represented as the phenotypic growth rate. I'm speculating that under stressful environment, slower growth (metabolism) may be advantageous. Plants in extreme environments (arctic, desert, epiphyte) has slower growth for this reason.

Here is a recent review of related topic: http://aob.oxfordjournals.org/content/early/2011/10/30/aob.mcr277.full

Sorry if this is too technical...


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## Trithor (Jun 24, 2014)

Very interesting and exciting observation!


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## eteson (Jun 24, 2014)

Many thanks for your comments.

Well First of all... I do not even know if the plants are true polyploids.... I made the treatment but the plants have not been tested for polyploidy yet.

Regarding to the statistics suggested by naoki... unfortunately it is too late, all the flasks have been replated or destroyed.

Some example:

-The most noticeable case was in the cross andreettae x longifolium:
I made 40 mini flasks (10 plants each) 20 untreated and 20 treated with Oryzalin. None of the untreated plants survived, but about 20% of the treated plants are fully recovered and growing quite fast by now.

-About the same in the cross manzurii x andreettae but in this cross some untreated plants survived (about 2-5%) while in treated plants survival rate was higher (15-20%)

-In andreettae x sib (25 flasks) for example, we lost 100% (no difference between treated and untreated).

-In besseae x andreettae most part of the plants survived but the plants were much bigger than in the others casses.



I think that another factor to be considered is that the treatment slows down the growing rate and plants treated and untreated are not at the same developmental stage... could be a plant in lower developmental stage (PLB) more resistant to stress than a differenciated one?

BTW naoki many thanks for the interesting paper!

Eliseo


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## naoki (Jun 24, 2014)

If we consider individual plants (rather than individual flasks) as the unit of observation (not the best way to do stats but that's ok for this), you are right that it is statistically significant (p=0.0015)! When I pool all 4 crosses (again, there is a better way to deal with this, but it's ok for this purpose), you get:


__________ dead ________ survive _____
-oryzalin: 200+190+250+0 0+10+0+200
+oryzalin: 160+170+250+0 40+30+0+200

So there is something which makes the oryzalin treated plants to make it heat tolerant. And you mentioned, majority of the treated plants are probably not 4x, right? When I used colchicine to Arabidopsis, I got <10% of 4x plants (and most of them are somewhat weird looking). Do you usually get a higher success rate?

Whatever the reason for your observation, it is very interesting, and I'm glad that at least some of your crosses are surviving! It would be also interesting if the surviving ones in the oryzalin-treated plants are really 4x when you screen them.

I would expect that more mature plants can deal with stress better, but it's just my gut feeling.


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## naoki (Jun 24, 2014)

Eliseo, well, I was curious about this, so I did a quick search (even though I should be working), and I found this:

http://onlinelibrary.wiley.com/doi/10.1046/j.1365-313X.2002.01384.x/full

It is beyond my knowledge of plant physiology, but it seems to be related. Basically, one of the key enzyme to induce the response to heat (heat shock-activated MAPK) get activated by oryzalin (which destabilize the cell structure, called microtubules). Well, I could barely understand the abstract, but this could be a part of the reason why you observed a higher survival rate for oryzalin-treated plants. I guess most people here (other than biology geeks) won't care about this, but thank you very much to bring this up, Eliseo!


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## eteson (Jun 24, 2014)

naoki said:


> If we consider individual plants (rather than individual flasks) as the unit of observation (not the best way to do stats but that's ok for this), you are right that it is statistically significant (p=0.0015)! When I pool all 4 crosses (again, there is a better way to deal with this, but it's ok for this purpose), you get:
> 
> 
> __________ dead ________ survive _____
> ...



Many thanks naoki!

We are just starting with polyploidy treatments in Paphs and Phrags so I cannot give you a number about our success rate. In Cattleya we have got about 10 % of surviving plants converted and as you say some of the plants are weird looking with recurved leaves and weird growth habit...On the other hand the Phrags surviving have almost normal habit... maybe thicker leaves... (I can take some pictures).

About the second paper you posted... Sorry I got totally lost in the abstract...


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## Ozpaph (Jun 27, 2014)

very interesting. Thank-you all.


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