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Assimilate allocation and carbon reserves in Juglans
regia L. seedlings
André Lacointe, . Inra, . Universite
To cite this version:
André Lacointe, . Inra, . Universite. Assimilate allocation and carbon reserves in Juglans regia L.
seedlings. International Symposium Forest Tree Physiology, Sep 1988, Nancy, France. �hal-02854781�
Assimilate allocation and carbon
reserves
in
Juglans regia
L.
seedlings
A.
Lacointe
Station de
Bioclimatologie,
INRA, Domaine-de-Crouelle, F-63039 Clermont-Ferrand, FranceIntroduction
This
study
was undertaken to answer 3questions,
some of which have been debatedby
severalauthors,
e.g., Hansen(1967)
and Kandiah(1979)
onapple
treesor Petrov and Manolov
(1973)
onpeach
trees. Can a
growing
organsimultaneous-ly
be active as astorage
organ?
Is agiven
storage
area active at different times? Are thedynamics
of reserves different be-tween the stempart,
which will bear thenext
year’s shoot,
and the rest of thestem?
Materials and Methods
Plant material
Walnuts
(Juglans regia L.)
were sown outdoors, on 5 June 1986, in individual pots provided withan automatic
irrigation
system. Germinationoccurred around June 20th. The stem
elonga-tion was
initially quite
fast untilearly July,
build-ing
up the ’lower stem’ with scaly leaves, then much slower,building
up the ’upper stem’ with true leaves.!4C
feeding
On
August
1st(late primary growth; only
a few short internodes were stillbeing
built: Fig. 1 ), 72plants were selected for
homogeneity
and fed for 5 h with14
C0
2
using
alarge
assimilationchamber; 24 planis at a time received a total of 18.5 MBq (500 uCi). Another set of 72 plants
were fed on October 8th
(primary
growth hadstopped
in lateAugust).
2-3 plants weresam-pled
theday
afterfeeding
and 3 d later, then 8-9monthly
until bud-break(late May).
They were divided into 5perennial
organs(Fig.
1),plus leaves when present, frozen in
liquid
nitro-gen, freeze-dried andweighed.
The 14C distribution was
analyzed
qualitative-ly by autoradiography and quantitatively with an
argon-methane
flow counter afterdry-grinding.
Results
Autoradiographs!
(schematic
drawings,
Fig. 2)
The
taproot
In both
experiments,
thelabeling
pattern
was stable after 3
days
and remainedunchanged
until bud-break. In theAugust
experiment,
unlabeled wood was pro-duced from the c:ambial zone, from currentassimilates in late summer. The October
labeling,
however,
showed that woodpro-duction had
stopped by
thattime,
since noand the central
parenchyma (the
predomi-nanttissues)
were ratheruniformly
labeledin both
experiments.
The upper stem
Although
it was notquite
clear beforeearly
September
in theAugust
experiment
because of thehigh
amount of!4C,
thelabeling
patterns
seemed stable after afew
days
here too.They
were,however,
quite
different between bothexperiments.
InAugust,
most of the !4Cincorporated
into thewood,
whereaspith
and cortex werepoorly
labeled. But this is trueonly
of the lowerpart
of the upper stem. In theapical
part,
theprimary
tissues werestrongly
labeled, whereas no !4C could bedetected in the wood
(autoradiographs
performed
fromSeptember on):
the woodwas
produced
after !4C treatment, fromcurrent unlabeled assimilates. This
proba-bly
reflects thegrowth
pattern.
However,the
boundary
between lower andapical
parts
wasalways
situated at a node:whether this
’step’-functioning
of thecam-bium was a result of a
particular
pattern
ofprimary growth
or not is not clearyet.
In contrast, the distribution
pattern
of 14C concentration after the October
la-beling
wasquite simple:
none in thewood,
little in the cortex, a little more in the
pith
and a lot in the buds and the abscission zones which were active at that time.
Quantitative allocation of 14C among organs
In both
experiments,
the totalradioactivity
recovered in theperennial
parts
was ca200
kBq (6 pCi)
perplant.
The leaves retained up to fall ca 100kBq
(August
labeling)
or ca 40kBq
(October labeling).
The
general
pattern
of distribution among organs(data
notshown)
wasstable after 3 d and remained constant for the duration of the
experiments.
Most of theexported
’14C was recovered in thetaproot
in bothexperiments.
However,
much more !4G was found in thetaproot
after the Octoberlabeling (80%)
than afterthe
August labeling (55%).
This differencewas also visible in the
plots
of thespecific
radioactivities
(SR) (Fig. 3).
Moreover,
the SR of the upper stem wassignificantly
higher
than that of the lower stem in the Octoberexperiment,
whereasthey
were similar in theAugust experiment.
There were,
however,
someslight
varia-tions with time(Aug.
exp., TableI).
Inautumn, the
newly
accumulateddry
matterwas labeled less than that
already
inplace
(compare
DMW andSR).
There wasapparently,
however,
someradioactivity
still
circulating
within theplant,
since thetotal
radioactivity
of the upper stemin-creased
slightly,
butsignificantly.
The upper stem was astronger
sink than the lower stem(cf.
their DMWratio).
Inwinter,
there was a
slight
decrease in the DMW ofSR: the
disappearing
DM wasmostly
made of unlabeled late reserves.
How-ever, as can be derived from the lower
stem
TR,
someslightly
labeled materialwas also lost. The lower stem was
de-pleted
faster than the upper stem.Discussion and Conclusion
Similar to the
findings
of Hansen(1967)
and Kandiah(1979)
onapple,
and ofothers on other
species,
theexport
of assimilates in walnut was directed moredownwards in autumn than in summer.
This was
apparently
related to thechang-ing growth
pattern
of the aerialpart,
whereas thetaproot
appeared
to functionas a
reserve-accumulating
organ after either theAugust
or Octoberfeeding,
whether it was
undergoing
cambialgrowth
or not.Moreover,
the whole of thestorage
area,
namely
the centralparenchyma,
appeared
to be active at all times.In
winter,
the differentdepletion
rates between the 2parts
of the stem wasper-haps
an indication of a transfer ofreserve-derived nutrients from the lower to the upper
part,
where thepreparation
of bud-breakprobably
resulted in ahigher
meta-bolic
activity.
References
Hansen P.
(1967)
!4C-studies onapple
trees. Ill. The influence of season on storage andmobilization of labelled
compounds. Physiol.
Plant 20, 1103-1111 l
Kandiah S.
(1979)
Turnover ofcarbohydrates
in relation togrowth
inapple
trees. II. Distributionof !4C assimilates labelled in autumn,
spring
and summer. Ann. Bot. 44, 185-i95
Petrov A.A. & Manolov P. (1973) Autumn
accu-mulation of reserve !4C-labelled assimilates and their