Re: Chimeric variegation and its pitfalls

From: Steve Marak <samarak at arachne.uark.edu> on 1997.11.23 at 02:37:34(1653) I have a fascination with variegation (as well as contorted plant forms) and have been waiting for the weekend and some time to get in on this discussion. For those who would like to read more about chimeric variegation, I recommend: http://aggie-horticulture.tamu.edu/syllabi/clasnotes/201notes/chimeralec/ chimeras.html (Please note that's all one long line.) This is a lecture by Dan Lineberger at Texas A&M, and I found it a concise summary. Unless you are already very familiar with this subject, though, don't expect to speed read it - it takes some thought. It's easy to see how variegation can result from a chimera in which one group of cells for some reason lacks (some or all) chlorophyll or other pigment. It's also easy to understand how such a chimera might "revert" - any time the plant is grown under conditions which sufficiently favor "normal" cells, the variegated line of cells might well die out, leaving only the normal. Often I have seen, in the growing hints for variegated plants, something to the effect of "needs more light than the normal form to retain good variegation". I've always assumed that this was because in high light the normal cells could produce plenty of food to go around, while in lower light those cells which must live on charity find survival much harder. I haven't seen anyone actually state this, though it seems consistent with observed results: leaves of variegated plants grown in low light lose some or all of their variegation, compared with older leaves which formed in higher light, and when moved back to high light, new leaves usually regain their abnormal coloring in all its glory. Once any leaf has opened, however, its coloring is fixed and won't be affected by changes in light level. My further assumption is that even if a variegated plant is grown in low light for some time, so long as the variegated cell line is still present in the meristem, the plant can regain its coloration when moved to higher light. A question: does that mean that such a plant, if left in low light conditions long enough, would completely revert to normal because all variegated cells, even in the meristem, would die? I'm not sure I can accept it - it doesn't seem like the cells in the meristem would be selected against for presence or absence of chlorophyll. The URL given above also discusses briefly why some kinds of variegation are more stable than others - some are very consistent, while others routinely produce both non-variegated shoots which much be pruned off and completely achlorophyllous shoots, as well as shoots with varying amounts of "normal" variegation. Apparently there are several other causes of variegation, including the viruses that Sean mentioned, something called "chloroplast mosaics" about which I know nothing, and of course genetics. I believe Jim Waddick gave the statistic that 95% of all variegation was NOT caused by virus, which I am pleased to hear. I'd appreciate any pointers from the group to good resources on variegation and contortion, whether on the Web or not. Steve +More -- Steve Marak -- samarak@arachne.uark.edu

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