Creative Commons Cole Shatto. Click for link.
In the murky redwood forests of California and Oregon grows the elusive albino redwood (Sequoia sempervirens). You may remember redwoods from their fame as the tallest trees on Earth. The albino variety grow as sprouts from the base of mature redwoods, a preferred form of reproduction in mature redwood forests where it is too dark for seeds to germinate. When the tree keels over, normal sprouts will be ready to take its place. Unless the sprouts are white — and thus totally incapable of feeding themselves. I’ve seen many a parasitic, achlorophyllous plant in my day, but they are all small and feed off the roots of others. Most trees are free living, and so any albinos they produce — which apparently does happen — won’t make it long (mycorrhizal fungi can’t save them because they need the food from photosynthesis too). But when your mom is 300 feet high, she’s probably making enough food to support a 5-60 foot freeloader.
Here’s a nice video showing from a public television station telling you more about these beauties. The guy at the beginning and end is a little over the top for me, but I love the park docent in the middle.
Mr. Kuty one mistake: he meant to say not that redwoods have six chromosomes instead of two, but that redwoods have six copies of their chromosomes instead of two copies (one from mom, one from dad), like us. That is, they’re hexaploid. Plants are known for their polyploidy; somewhere between 30 and 80% of them are, and they seem able to tolerate a fusion of gametes where meiosis was incomplete in one or both, or to hybridize with related plants in ways that would would devastate development or render offspring sterile in most vertebrates. Suddenly doubling the number of chromosomes also reproductively isolates plants, and seems to be a major source of new species. This can even happen between species. In the plant world, a quadriploid (4x) wheat plus a diploid (2x) rye = hexaploid (6x) triticale. Duplicating sets of chromosomes can have interesting effects. Hexaploid wheat make a much meatier head of grain than diploid wheat.
* Triploid crops: apple, banana, citrus, ginger, watermelon
* Tetraploid crops: apple, durum or macaroni wheat, cotton, potato, cabbage, leek, tobacco, peanut, kinnow, Pelargonium
* Hexaploid crops: chrysanthemum, bread wheat, triticale, oat, kiwifruit
* Octaploid crops: strawberry, dahlia, pansies, sugar caneSome crops are found in a variety of ploidies: tulips and lilies are commonly found as both diploid and as triploid; daylilies (Hemerocallis cultivars) are available as either diploid or tetraploid; apples and kinnows can be diploid, triploid, or tetraploid.
Scientists aren’t sure about the origin’s of Coast Redwood’s six sets of chromosomes — whether they came from the same species or from a hybridization of two, but there’s evidence it might be from two (AAAABB). Polyploidy is somewhat unusual for conifers. Also unusually for conifers (and for any life in my understanding), its mitochondria are inherited from sperm, not eggs. As you may know, mitochondria are subcellular organelles that produce energy for the cell. They take up space. Eggs are big, and they usually contribute all the mitochondria to a new zygote, which is why in humans, mitochondrial diseases always come from your mother. Yet in redwoods, that doesn’t seem to be the case. Which begs the question: what do redwood sperm (like all gymnosperms and flowering plants, found inside the pollen grain) look like?
Here’s another interesting little coincidence: in addition to being hexaploid (6x), Sequoia sempervirens has exactly 66(!) chromosome, implying the original species had 22. Chromosome number isn’t really meaningful (since chromosomes can have arbitrary lengths), but just for the record, we have 23. : )
Here’s what I still don’t understand: if these things are simply clones that sprout from the base (botanists call them “suckers”), why are they not genetically identical to the parent? Hmmm. . . . In the video and in this story on NPR, they seem to imply that the plant’s hexaploidy is involved . . . but no one gives a mechanism. Without sex, whence the novelty? (if I had a dime for every person who’s asked that question . . . )
Quote of the day: “It’s just that this offspring is the one that sits on the couch rather than going out and getting a job.”
Course, one might still argue that is parasitism. : )
Redwoods, by the way, are in the family Cupressaceae. Their closest relatives are the dawn redwoods (an amazing story of a fossil species presumed long dead discovered alive in a temple in China during World War II) and giant sequoias, the largest trees on Earth. Other relatives include junipers (of gin flavoring fame), cypresses, arborvitae, and the famous southern swamp tree bald cypress.
Merry Christmas, everyone*! For more lovely photos of the albino redwood, click here and enjoy. : )
*In a totally non-sectarian, universal holiday cheer sort of way. Idea for this post brought to my attention by Kati Dimoff. Thanks, Kati!
{ 2 trackbacks }
{ 4 comments… read them below or add one }
a live replacement for the “flocked” christmas tree! now if only i could find a pink one, i’d be sold! so interesting. i really want to know how it works since they are supposedly just clones.
ps. i love stories like the dawn redwood story. :) merry non-sectarian, universally cheery christmas to you, too!
“murky” !! Have you ever been in a redwood forest? They are spectacularly beautiful.
I get your point, but they are no darker than any other old growth forest. Maybe less so.
It’s true that I have not. I read that they were very dark though. But perhaps murky *is* a bit of an overstatement. Thanks for pointing out. : )
This article omits a couple ideas important to understanding the phenomenon of Albino plants:
1. All chlorophyll resides in the chloroplasts within plant cells and chloroplasts have genes of their own. Chloroplasts can be lost from plant cells or loose their ability to make chlorophyll without any change in the plant’s nuclear genes. Sometimes a nuclear gene may be involved in disabling chloroplasts (because a few genes have moved from chloroplasts into the nuclear genome) but more often a chloroplast gene is involved. Chloroplasts that loose the ability to make chlorophyll may still increase in number within cells and by random sorting during cell division some cells may end up having only nonfunctional chloroplasts and thus be albino.
2. Plants are very different from animals in the way they build their more indeterminant bodies. They have localized growing tips or zones that remain embryonic called meristems (while mature animals have dispersed stem cells for regeneration). If by the sorting process mentioned above, all cells in the shoot meristem loose all functional chloroplasts, the entire shoot that they give rise to will be albino. Meristems vary among plants from single cells to aggregates of cells, and more complex aggregates in which certain cells give rise only to certain portions of the shoot. When only certain cells in a more complex meristem lack functional chloroplasts, stable variegated shoots may be produced as is seen in many horticultural selections. In less rigidly organized meristems, variegation may be unstable and change as the shoots develop and branch, usually sorting out into green and albino branches eventually.
An hypothesis: Stable variegation does not seem to occur in coast redwood. The closest thing would be the cultivar sold as S. sempervirens ‘adpressa’ and several other names. This is a different type of phenomenon in which chloroplast competence is delayed so tip growth is white until fully mature. The coast redwood meristem is of the simple type and when dysfunctional chloroplasts are present in an individual, sorting yields either normal or pure albino shoots. The group of trees growing together that all have albino shoots at the base may all have arisen from one individual after fire. That individual had a masked population of nonfunctional chloroplasts that is revealed when cell sorting produces albino meristems. I would like to know if climbing the trees would reveal higher albino shoots, or if something unusual is happening in the lignotubers of these trees?