451
Isoenzyme uniformity in western red cedar seedling s from Oregon and'Washington
DONALD L. COPES
United States Department of Agriculture, Forest Service, Pacific Northwest Forest and.Il.iiizge Experiment Station, Portland, OR, U.S.A. 97232 Received July 29, 1980
1
Accepted January 16, 1981
CoPES, D. L. !981. Isoenzyme uniformity in western red cedar seedlings from Oregon and Washington. Can. J. For. Res.
11: 451-453.
Isoenzymes of newly germinated western red cedar seedlings (Thuja plicata Donn ex D. Don) from western Oregon and
eastern and western Washington lacked variation in band patterns of nine enzymes. The isoenzyme results indicate that western
red cedar populations contain very little genetic polymorphism. Management of the species will likely be more productive if
concentrated on cultural practices rather than on intensive genetic improvement.
CoPES, D. L. 1981. Isoenzyme uniformity in western red cedar seedlings from Oregon and Washington. Can. J. For. Res.
11:
451-453.
En utilisant de jeunes semis de Thuja p/icata Donn ex D. Don, originant d'une partie occidentale de !'Oregon et de
Washington et d'un secteur oriental de ce demier etat, !'auteur obtint un manque de variation des isoenzymes dans les modeles
de neuf enzymes. Ces resultats indiquent que les populations de Thuja plicata offrent tres peu de polymorphisme genetique.
Ainsi, l'amenagement de cette espece semble plus prometteur si on intensifie davantage les pratiques culturales plutot que de
viser a une amelioration genetique.
[Traduit par le journal]
In 1977, I conducted an electrophoretic survey of
Natural populations lacking enzyme variation are
rare. When such populations exist, they are often on the
extreme margins of a geographic distribution or they are
newly germinated seedlings from two western red cedar
inbreeding colonizers (Brown 1978). Most forest tree
populations are genetically heterogeneous (Hamrick
et a!. 1979). One exception, Pinus resinosa Ait., has
extremely low levels of genic heterozygosity (Fowler
I found no variation in the band patterns of the six enzyme systems. and Morris 1977).
The amount of genetic variation in western red cedar,
from widely separated sites in Oregon and Washington. The following study reports the results of an electro­
populations near the Oregon coast. The purpose of the
survey was to determine the level of genetic diversity. In 1979, I obtained seed from western red cedars Thuja plicata Donn ex D. Don, has been difficult to
phoretic study on recently germinated seedlings grown
assess. Variation should be expected since its natural
from the 1979 seed. Nine different enzyme systems
range extends from southern Alaska to northern
California, from the Pacific coast to western Montana, were examined for evidence of genetic variation.
and from sea level to 2100 m. Throughout this range,
the soils, climate, and associated plant species differ
(Fowells 1965). Tree form is altered with changes in
environments and tree age (Day 1957). Provenances
differ in growth (IImurzynski et al. 1968), in leaf blight
resistance (Sr,6egaard 1956), and in frost resistance
(Sakai and Weiser 1973).
Other evidence indicates western red cedar has low
amounts of genetic variation. Leaf oil terpene composi­
tion is uniform both within and between coastal and
interior populations and only slight differences are
found between the most widely separated populations
(von Rudloff and Lapp 1979). Seedlings of western red
cedar grown in a uniform environment varied much less
in size than did seedlings of six other forest tree species
grown under the same conditions (Minore 1969).
1
Revised manuscript received January 14, 1981.
Methods Seed from 49 trees was sampled (Fig. I); 30 trees from five
geographically separated sites were in western Oregon, 8 trees
were from eastern Washington and II trees were from west­
em Washington. All sampled trees grew fat enough apart to
prevent common ancestry. Seed was stratified, germinated,
and grown in fine sphagnum peat in a 2!°C growth chamber.
Newly germinated seedlings (1.0-2.0 em) were macer­
ated in 20 p.L of gel buffer solution containing 4.5% poly­
vinylpyrrolidone (molecular weight 40 000). The fluid extract
was absorbed onto 5 X 13 mm paper wicks and then stored
at -27°C (Copes and Beckwith 1977). The electrophoretic
apparatus was similar to that described by Conkle (1972).
Procedures were described by Copes and Beckwith (1977).
Extracts from 20 seedlings from each seed tree were placed
in two or more gels in order to eliminate between-gel
irregularities.
Gel slices were analyzed for nine enzyme systems:
esterase, acid phosphatase, and leucine aminopeptidase
CAN. J. FOR. RES. VOL.
452
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.;.
••
II,
1981
..
0
(+)
100
81
79
69
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J
56
- 4.
44
FIG. I. Map of Oregon
and Washington
56
50
50
44
47
44
44
showing the
41
approximate location of western red cedar seed trees whose
25
progeny were examined electrophoretically for enzyme poly­
morphism. Dots indicate tree locations.
49
0
28
31
25
-::-:-;-------- (
Origin
-----
-
)
(Scandalios 1969); glucosephosphate isomerase and glu­
Fto. 2. Monomorphic banding patterns for nine enzyme
tamate dehydrogenase (Shaw and Prasad 1970); peroxidase
systems were found in extracts from newly germinated seed­
and glutamic oxalacetic transaminase (Brewbaker er a!.
lings of western red cedar. Underlining denotes isoenzymes
1968); tetrazolium oxidase (Baur and Schorr 1969); and
fluorescent esterase (Mitton era!. 1979). The band patterns
on each gel slice were recorded and relative mobilities
calculated.
that consistently occurred on the gels. No underlining denotes
Results and discussion
A total of 19 clearly stained isoenzyme bands was
found (Fig. 2, solid lines). The same 19 bands were
found in every seedling. Four additional bands (Fig. 2,
no underlining) gave inconsistent results; they appeared
erratically in a few gels, but were absent in other gels
containing extracts of seedlings from the same seed
trees. The inconsistent bands may be secondary pro­
ducts arising from physical or chemical alterations of
the original proteins, and they are not considered to be
true genetic variants.
No genetic variation was detected. Every seedling
produced all 19 bands. The lack of isozyme variation in
western red cedar implies that the species is genetically
uniform. This conclusion is consistent with the leaf oil
terpene results of von Rudloff and Lapp (1979).
The lack of isoenzyme variation in western red cedar
cannot be attributed to the particular techniques or
weakly and inconsistently stained isoenzymes which were
most likely chemical alterations of the original proteins.
enzymes assayed. The nine enzymes examined in this
study are usually polymorphic in other conifers (Mitton
eta/. 1979; Copes 1975, 1979). Additional electro­
phoretic runs, made on seedlings from the same seed
trees but with different extraction buffers, revealed no
variation in isoenzyme patterns. The same apparatus
(Conkle 1972), buffer systems (Scandalois 1969), and
staining methods (Shaw and Prasad 1970; Brewbaker
et a/. 1968), have routinely shown enzyme poly­
morphism in other conifers.
Pinus resinosa, depauperate in isoenzyme variation
(Fowler and Morris 1977), is remarkably uniform in
growth rate, morphology, phenology, and photoperiod
(Fowler and Lester 1970). These authors suggest that
the lack of genetic diversity in red pine may have
resulted from an evolutionary bottleneck associated
with past glaciation.
Western red cedar also is remarkably uniform in
growth rate, morphology, phenology, and photoperiod,
NOTES
but it is difficult to postulate a similar cause for western
red cedar. A small relic parent population could not
have resulted from an east-west barrier since the
mountain ranges in the study area are oriented in the
north-south direction. An additional indication that a
physical barrier has not reduced this species to one
small area is the abundant genetic variation exhibited by
associate plant species (Copes and Beckwith 1977;
Copes 1979; Yang et at. 1979). Isoenzymes of asso­
ciate species show no evidence of a genetic bottleneck.
The Jack of isoenzyme variation suggests that
management of the western red cedar by cultural pro­
cedures will yield greater returns than intensive genetic
improvement programs. Results from this study raise a
number of questions. First, how does this species with
little apparent isoenzyme variability grow and compete
under such a variety of climates, soils, and associated
species? Are the nine enzyme systems not correlated
with adaptive systems which play a role in fitness?
Additional studies on growth-related traits, frost and
disease resistance, and isoenzymes are needed to see if
the results of the early studies were correct.
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