I think it has pretty much been shown that Ben's Rules of Thumb for
Hosta sports is seriously flawed. First, mitotic recombination just
isn't all that common to account for yellow hostas developing green
edges, besides the need for this to occure in the apical meristem.
Nuclear mutations are also a possibility, but again when we look at
the number of sports in hostas we have to question why the rate of
sporting seems to be so high compared to the normally low rate for
mutations. When we look at other genera we just do not see variegated
sporting like we see in hostas. If you look carefully at various
genera you will find variegated forms, but not as easily as with
hostas. Histological layer switching and replacment certainly does
play a significent role in hostas, but NOT as a causal factor in
The next step is to try to understand just what is happening. We have
the possibility of nuclear changes, including point mutations,
chromosome loss and damage and transposible elements; and secondly,
chloroplast mutations. Hopefully, if some of us can cooperate this
summer and next year we might be able to get some information about
the relative importance of nuclear versus chloroplast nature of
variegation in hostas. However, before we can move on we really need
to know what the histological composition of the hosta plant is. Are
hostas a three layer system with two tunic layers L1 and L2 and one
corpus or are hostas a two layer system with one tunic over a corpus?
The difference may appear to be slight, but the two systems are quite
different in how we look at variegation.
In a three layer system the L1 and L2 layers maintain themsleves by
anticlinal divisions with a number of cells at the top of the apex
maintaining a perpetual zone of dividing cells from which all other
cells in that layer are derived from. In the L3 layer there is no
organized apical meristem as such. All the cells in the corpus region
can divide. In a two layer system there is the L1 layer with a apical
meristem and a corpus L2 where there is no apical meristem. In other
words, the L2 layer of a two layer system is equivalent to the L3 of a
three later system.
Now, here is where some confusion may arise. In both a two layer
system and a three layer system the gametes are formed mainly from the
L2 tissue, but the L2 tissue of a two layer system is completely
different from the L2 of a three layer system. In a three layer
system the L2 is a tunic with an apical meristem and anticlinal
divisions while in a two layer system the L2 is the corpus with NO
apical meristem and no control over how cells divide. This difference
might account for streaking and why streaking is often unstable.
The question I have, and maybe Ben can answer this, do hostas have a
two or three layered histogenic system? Does anyone have a
microphotograph of a hosta apex?
Now, another question for Ben. Ben, if you claim that green edges
arise on yellow leaved hostas via mitotic recombination, then how do
you get a yellow center on a blue hosta like in the sporting of
sieboldiana Elegans, a blue hosta, to Great Expectations, a yellow
centered hosta? So now where does the yellow come from! Or are we
talking about two different kinds of yellow?
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