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Science

Tree's Leaves Genetically Different From Its Roots 80

Posted by samzenpus
from the different-parts dept.
ananyo writes "Black cottonwood trees (Populus trichocarpa) can clone themselves to produce offspring that are connected to their parents by the same root system. Now, after the first genome-wide analysis of a tree, it turns out that the connected clones have many genetic differences, even between tissues from the top and bottom of a single tree. 'When people study plants, they'll often take a cutting from a leaf and assume that it is representative of the plant's genome,' says Brett Olds, a biologist at the University of Illinois at Urbana-Champaign who was involved in the study. 'That may not be the case. You may need to take multiple tissues.' The finding also challenges the idea that evolution only happens in a population rather than at an individual level. As one tree contains many different genomes, natural selection and evolution could happen within a single organism."
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Tree's Leaves Genetically Different From Its Roots

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  • by RichMan (8097) on Monday August 13, 2012 @11:27AM (#40973537)

    The grafting of fruit trees is very common.

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    http://youaskandy.com/questions-answers/25-article-series-1950/16332--why-do-we-have-to-graft-fruit-trees.html
    There are other advantages to grafting. A grafted fruit tree may be made to grow in new places. A peach likes sandy, wellsanded soil. The plum tree likes poorly drained soil. Peach can be grafted onto plum stock growing in soggy soil. Plum can be grafted ,into peach stock growing in looses sandy soil. So we get peaches and plums growing where they have never grown before.

    Grafting also helps to keep down plait pests and disease. Some fruit trees cannot be hurt by this pest or that disease. These trees form fine stock, though the fruit may be poor,.
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  • Re:Uh... Howzat? (Score:4, Interesting)

    by Russ1642 (1087959) on Monday August 13, 2012 @11:32AM (#40973623)
    Sounds like that's what they're saying. Different tissues reproduce in different ways. For example a tree can make seeds or produce offshoots from the roots. One way could be more successful than another so areas with different genes within a single tree could produce a differing number of offspring.
  • Re:Uh... Howzat? (Score:5, Interesting)

    by Anonymous Coward on Monday August 13, 2012 @11:39AM (#40973747)

    Actually, yes. That's exactly it. Think about the times you've seen a tree with a plenty of leaves, but with dead branches mixed in.

    Given the way that trees grow, this actually makes sense. Tissues in the trunk are only grown in a very narrow band located between the bark and the wood. If a mutation happens at some point during the tree's growth, it's possible that the new tissues will be more/less likely to survive given the current environmental circumstances. Those new tissues carrying beneficial mutations would be more common as the tree continues to grow. Leaves are an even more extreme example. If a given branch has tissues with a given mutation, the leaf buds on the tree will carry it, and the leaves will carry it. Branches with more productive leaves will live longer/better as a result. Given that trees can grow for hundreds of years, it's possible that the same tree may have had dozens of mutations in its genetic structure some of which were passed on to branches at different points in time, multiple of which could still be 'active' as a result.

    This is less likely to be the case for animals, since their tissues undergo complete replacement over a comparatively short period of time. That means a genetic sample from an animal would almost always only reflect the *current* genetic state of the animal.

  • Re:Uh... Howzat? (Score:4, Interesting)

    by Rhaban (987410) on Monday August 13, 2012 @11:44AM (#40973817)

    A mutation could happen in single cell, ar a group of cells during the tree growth, and then a leaf or an entire branch spawns from this cell.

    If cells in tree nodes are for some reason likely to be the subject of mutations, it's easy to imagine natural selection occuring at a cell level, with a branch growing from the fittest cells.

  • by Anonymous Coward on Monday August 13, 2012 @01:08PM (#40974827)

    The current theory, is that you would not in a "normal" human. The gene sequences should be identical in all healthy cells, with only the pattern of currently active genes changing between cells. Mutations later in life tend to result in cancer, not functional human tissue.

    However, there are known ways for this to not be true. Typically it has to do with the subject having absorbed siblings while in the womb. It would be interesting to find out how common that actually is in humans.

  • by bennomatic (691188) on Monday August 13, 2012 @01:19PM (#40974951) Homepage
    Maybe not completely irrelevant. Perhaps, in a given population of a species of tree, there is not only cross-pollination, but also cross-grafting. Maybe insects or higher animals move leaves or seeds from tree to tree, and for some reason, this species is more likely to accept the new introduction without complex grafting techniques.

    To wit: Tree A spawns tree B through pollination with tree C, so B is indeed genetically unique. B is close to A, though, and a bird gathering shoots for its nest brings over something viable from B to A and sticks it in the crook of a branch and it grafts. B' is born, effectively a grandchild AND parasite of A.

    I'm just letting my imagination wander here, but it certainly would be interesting if that were the case.
  • Re:Uh... Howzat? (Score:5, Interesting)

    by icebike (68054) * on Monday August 13, 2012 @01:47PM (#40975373)

    Well what they are really saying is that the upper parts of a tree can diverge from each other and from their root stocks via natural methods.

    Any orchard owner knows that its easy to graft dissimilar branches on a common root stock, producing, for example, two different types of apples from the same tree. Its easy, and farmers have been doing it for years. Who knows where this idea arose.

    Now it turns out that nature can do roughly the same thing, without all the cutting and splicing, but rather, by gene mutation or cross pollination or what ever.

    Clearly every seed germinates to a single plant, but over time, it appears that significant divergence can take place on a single living tree. This might be a significant evolutionary advantage, as some branches may survive frost, drought, or pests better than other branches. A built in diversity in a single tree.

    Perhaps we have to start thinking of some of these trees as colonies of organisms rather than a single individual.

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