This is something that also comes up relatively often with crossing of
two different but closely related species, but from a different
mechanism. Plastids, including chloroplasts and chromoplasts, have
their own genetic material. Plastids were originally an independent
organism (a photosynthetic cyanobacteria) which formed a symbiotic
relationship with early plant material. The current theory is that this
happened twice independently in plant evolution. Over time these
plastids have lost 90-95% of their genetic material. Most of it ended
up in the cell nucleolus. Thus the plastids have their own genetic
material, but it is under control of the nucleus genetic material.
There are biochemical signals sent from the nucleus which control the
genetics of the plastids. Each species differs some what from other
species in how these signals are sent and interpreted. When different
species are crossed, we can get a mistranslation of signals and the
plastids never get the signal to produce chlorophyll, and thus the
white seedlings, which don't survive unless there is a tiny amount of
chlorophyll. Sometimes these tissues are grafted onto a normal
chlorophyll plant for research purposes.
Usually these seedlings are solid white. In the streaked ones there
likely is a separate mechanism at work. This involves gene silencing.
this is where one gene, often paternal gene is turned off through
methylaion. Thus normally control of the plastids wou
ld be under
control of maternal genes. In inter species crosses this may not work
properly, so both of the plastid control genes (maternal and
paternal)are trying to do the job, and thus mixed messages are sent to
If this is indeed what is happening here there may be dramatic
differences in reciprocal crosses in regards to variegated foliage. Do
you have any information re reciprocal crosses?
still more broken color
Posted by: "Donald Eaves"
Mon Jan 5, 2009 8:18 am (PST)
So, Chuck, is it the same reactivation of inactive genes
that cause the
variegated foliage? A transposon at work? The occurrence of the
streaked with white is even more common in results from TBxAB than
color blooms. In this case of AUTUMN ECHO X KOKO KNOLL both occurred.
Unfortunately these plants aren't sturdy in my growing conditions and
don't survive for too many seasons. Last I looked this one was still
hanging on but has never done well. Too bad since the combo of broken
bloom with the white streaked foliage is a different stroke among the
Texas Zone 7b, USA