Re: Fw: Variegation-Vaughn-1979-1980
Dan Nelson wrote:
> Here another article from Dr. Vaughn on Variegation from the same issue of
> the Journal.
> Subject: Variegation-Vaughn-1979-1980
> Found in THJ Bulletin 11, 1979-1980 pages 33-34
> VARIEGATION IN HOSTA- by Kevin Vaughn
Preston had already sent this article to me. I had read it many years ago and
have remained impressed at the wonderful work of Dr. Kevin Vaughn. I am glad you
have forwared it to hosta-open so that all can read it. The work in pure science
lays the groundwork of understanding necessary to be more fully aware of the
REASONS WHY something is so or not so. The essence of Dr. Vaughn's work is the
explanations of the importance of plastid mutations as they affect inheritance
and explain the phenomena of chimeras. I have been studying and writing about
this subject (as a reporter, not a researcher) for many years now. I wonder how
many times must the explanations be repeated? Another 20 years? Some who write
(and edit) are indeed slow learners.
> Despite these results, I decided that I still liked HOSTA, was still
> interested in studying the variegation, and subsequently obtained a working
> collection. From this crossing work and later work using techniques of
> light and electron microscopy and biochemistry...the following conclusions
> were drawn:
> Chodat in 1919 classified variegated patterns in Hosta in one of two
> types: marginata and mediovariegata. The marginata type, represented by
> such clones as 'Louisa' and 'Frances Williams' have conspicuously lighter
> edges and a green center. Self or cross-pollinated seed from these
> varieties as the female parent give about 99% green and 1% mutant (yellow,
> white, or variegated). Mediovariegata clones, such as 'Maya' and 'Kabitan',
> in contrast to the marginata forms give a majority of mutant seedlings when
> used as the pod parent. All yellow Hosta behave in a similar manner to the
> yellow-centered forms. However, pollen from a variegated or yellow clone on
> a green plant give all green progeny.
> When one thinks about the construction of the Hosta leaf and the
> pollination process, a ready explanation pops forth for the breeding
> behavior of the variegated Hosta. The tissues from nearly all of the
> higher plants are derived from 3 layers of cells which are present at the
> growing tip of the plant. In Hosta, the central (L II) layer, or second
> layer forms the central area of the leaf and the ovules...while the L I
> forms the marginal tissue of the leaf and the epidermis (skin) of the entire
> plant. Thus, one would expect that since there are tiny proplastids or
> immature chloroplasts (the chlorophyll-containing body of the cell) in the
> ovules (derived from L II) that if the L II is mutant so would the
> seedlings. The pollen parent appears to have little or no influence on
> variegation. Thus one would expect that since the pollen of Hosta has
> probably no more than one proplastid and since many are supplied by the
> ovule; there is good cytological reason why only the maternal parent
> contributes the vast majority of variegation in Hosta (several exceptions
> are known, however).
> Thin sections through the capsules and leaves of Hosta show that it is
> possible for tissue from the L I to give rise to a small amount of the
> tissue from central areas of the leaf and a fraction of the total number of
> ovules. This is caused by excessive growth of the L I of "Frances Williams"
> and can give all golden sports whereas excessive growth of L II or a loss of
> L I by injury can give an all green plant.
> Recently I have begun experimentation with a series of mutagens to
> determine if it was possible to produce variegation in all green Hosta.
> Although the results are preliminary, a number of mutants have been
> produced, but a high kill rate is still common. By using less valuable
> seeds such as radish and tobacco, we are gradually working out mutagen doses
> which optimize mutation yet allow a normal amount of germination.
> Electron microscopy studies of mutant Hosta are also in their infancy.
> One of the main "whys" about Hosta was why the large number and variety of
> plastid mutants. I felt that an EM study would give us more of a clue.
> Within each chloroplast there are membranous sacs where the pigments
> (chlorophylls & carotenoids) are attached. In green plants these
> thylakoids lie in stacks whereas in the yellow 'Wogan Gold' they lie spread
> throughout the chloroplast. Interestingly some species in the tropics have
> similar levels of chloroplasts and thus these yellow Hosta may also be more
> efficient in some environments at light-gathering. Strikingly different are
> the chloroplasts of the white edge and centers of the white variegated
> clones. These varieties start with normal thylakoids and later an extreme
> swelling or 'exploding' of these thylakoids is apparent. This allows the
> pigments to be destroyed (which explains why these plastids show white
> markings). Various white clones vary to the extent of the 'exploding', with
> the cleanest white clones exploding rapidly. There appears to be even good
> biochemical reasons why certain Hosta have white or yellow variegation and
> this work will be reported in various other journals.
> This is the 100th anniversary of the use of Hosta as a research
> organism. With the many intriguing problems of this genus, it will surely
> keep scientists hopping for another 100.
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