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Chloroplast Mutants in Hostas...Vaughn


Scholars,

In my attempt in this discussion to prepare an interprative summary of
the Vaughn article, "Chloroplast Mutants in Hostas", my only purpose is
to be helpful to readers. At the same time I wish to show my
recognition  and high regard for Dr. Vaughn's work. He has been honored
by the American Hosta Society and justly so, for the contributions he
has made in better understanding of causes of variegation in Hostas and
the importance of maternal ionheritance mechanisms, which are based on
plastid mutants in the cytoplasm  of the cells.of Hosta plants. It is a
very complex subject and not easily understood. There have been a host
of scientists who have dedicated many years in the study of this
subject. Vaughn reviews their achievments as he describes his own work.
Thus a comprehensive review of the literature is provided to prove the
validity and relevence of statements made.I will try to mention the most
important of these in my brief summary . I hope my efforts are less like
a cartoon when I would prefer it to be more like a description of a
masterpiece painting. If I fail in my efforts, I request your
forgiveness and understanding.

In the Introduction, Vaughn indicated interest in research techniques
applicable to higher plant genomes. Hostas appear to be highly suitable
for many kinds of chloroplast research because of the large number of
mutants found, beginning with the work of Yasui in 1929.Vaughn's work
continues that of Yasui in maternally inherited mutants and interprets
chimeras in Hostas.The work of Neisen-Jones  (1969) further explained
some of these mutant type chimeras.

A discussion of the work of Dermen( 1947 to 1960) covered an explanation
of the LI , LII and LIII histological tissue layers in meristems. Such
genetic analysis of progeny, it was explained, helps us understand the
histology of the mutations involved and whether they are nuclear or
plastid genes involved in control of these phenomena.

Vaughn described his Materials and Methods used in his breeding
experiments to record the mutant characteristics which resulted.Five
plastid mutants were identified , described and classified into
marginata, mediovariegata,aurea, snow flurry and mosaic types, along
with the inheritance characteristic in each type of mutant plastid
involved..The stability of each mutant class was classified with most (
with the exception of Mosaic) being relatively stable. Seasonal
stability characteristics were noted for some classes.

In the Discussion Section, Vaughn stated that Dermen found (  1960) that
the LII histological layer produced the ovule tissue which produced
progeny which were 100 percent mutant.and tha LI mutant tissue was
responsible for marginata progeny. The cite for genetic control for most
of the plastid mutants is in the plastids themselves according to
Tilnet-Bassett (1975). It was stated that a large range of colors and
seasonal variation in Hostas suggests that a complex system within the
plastid genome  must exist to account for all of these phenotypes. In
the case of H. 'Purple Profusion' mosaic variegated offspring seemed to
demonstrate a type of "sorting out" mechanism due to plastogenes rather
than a (nuclear) controlling element system  according to Kirk and
Tilney- Bassett, (1967).

Reference was made to the "licorice stick"  spiraling of 'Frances
Williams' bloomscapes, closely related to replacement (from LI) which is
part of the replacement/displacement system described by Stewart and
Dermen (1970). Virescent mutants as in 'August Moon' (described by von
Wettstein, 1959) were noted as being affected by exposure to light.

Vaughn concluded that the Genus Hosta seemed uniquely suited for study
of chloroplast genetics because of :

1. large numbers of different mutants available
2. the mutants are readily distinguishable because hosta has only LI and
LII  in leaves and these layers are distinct.
3.the mutations occur in many of the species and cultivars
4. several types of unusual changes in morphology and tissue layer
shifts occur.

An extensive biobliography followed the text.


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