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- Comparison between the structure and function
of chloroplasts at different levels of willow canopy
during a growing season
A. Nurmi H. Vuorinen
21
E. 1
Vapaavuori 1
T. Kangas
1 Finnish Forest Research Institute, Suonenjoki Research Station, SF 77600 Suonenjoki, and
The
2
University of Helsinki, Department of General Botany, SF-00710 Helsinki, Finland
Introduction fit with their function by measuring the rate
of gas exchange under the prevailing envi-
ronmental conditions in the canopy.
Light climate has a strong impact on the
ultrastructure of chloroplasts. There is
plenty of evidence that the degree of
grana stacking in chloroplasts of plants
Materials and Methods
grown in high light is less than in plants
grown in low light (e.g., Lichtenthaler et
al., 1981which is also the case for plants
The willow stand (established in 1980, 125 m 2
adapted to sunny or shady habitats in area) was cut down before the growing sea-
(Boardman, 1977; Aro et al., 1986). Very son 1986 and measurements were made on
little is, however, known about the sea- leaves that emerged on new shoots success-
ively throughout the growing season. The stand
sonal acclimation process of the photo-
was fertilized with a commercial fertilizer (Pu-
synthetic apparatus in the canopy, where utarhan Y-lannos 10-16-17) once a week
leaves that are initially exposed to full sun-
during the growing season, so that it received a
light are transferred through half-shade total of 150 kg of N/ha/season. The stand was
into full shade. In conditions, under which watered regularly to assure that the plants were
not water-stressed.
water and nutrient availability are not limit-
ing growth, the shaded leaves remain The samples for electron microscopic exami-
nation were taken from 3 replicate plots at 6 dif-
intact for most of the growing season. This
ferent dates from upto 5 different heights (Fig.
suggests that the leaves retain a positive
1 A}. The samples were treated as described by
carbon balance by acclimating to the
Vapaavuori (1986) and Aro et a/. (1986). The
changing light climate. In this study, we grids were examined on a Jeol 100B electron
quantified the seasonal changes in the microscope. Before prefixation of the samples
for electron microscopy, the photosynthetic
chloroplast ultrastructure at several
capacity of the leaves was measured at prevail-
heights of a willow (Salix cv. Aquatica ing light and temperature conditions by means
gigantea) canopy. We also determined of a C0 porometer (ADC LCA-2, the Analytical
2
how changes in chloroplast ultrastructure Development Co. Ltd., U.K.). The chloroplast
- ultrastructure
was analyzed from the electron Results and Discussion
micrographs as described by Aro et aL, (1986)
and Vapaavuori (1986). On an average, 6 typi-
At all studied levels of the canopy, the
cal from each
chloroplasts were analyzed
sample of the 3 replicate plots. ratio of the total length of appressed to
- quantum flux densities (Anderson and
non-appressed thylakoid membranes was
lowest (0.9-1.4) in the youngest leaves Osmond, 1987). At level 1 (60 cm above-
(Fig. 1 B) that were exposed to sun (Fig. ground) the ratio increased slightly until
2B). The thylakoid structure in these the middle of July (Fig. 1 B), but remained
leaves was similar to that in plants adapt- typical of sun-exposed leaves (below 1.3).
ed to sunny habitats or grown at high During this period, the low rates of C02
l
0
2 PHOTOSYNTHE! I S . A
- uptake recorded (Fig. 2A) were possibly of the length of appressed to non-
caused by decreased availability of excita- appressed thylakoid membranes (Fig. 2A)
tion energy in the canopy and not by alter- and between the ratio of the length of
ed organization of thylakoid membranes. appressed to non-appressed thylakoid
Later in the growing season, the chloro- membranes and photon fluence rate (Fig.
plast ultrastructure acclimated to de- 2B). This suggests that, in the canopy,
creased light (Fig. 2B) and the low rates of acclimation of the thylakoid structure to
decreasing photon fluence rates will lead
C0 uptake (Fig. 2A)
2 possibly
were
caused by altered thylakoid structure typi- to gradual impairment of the photosynthe-
cal of shade plants (Lichtenthaler et aL tic capacity.
1981Part of this reorganization in thyla-
koid membranes might also be due to
ageing, since the area of plastoglobuli of
chloroplast area increased (data not
shown), which is known to be an indication References
of ageing (Hudak, 1981).The pattern of
thylakoid organization at level 2 (110 cm
aboveground) was similar to that at level Anderson J.M. & Osmond C.B. (1987)
1; only the appressed/non-appressed Shade-sun responses: compromises between
acclimation and photoinhibition. In: Photoinhibi-
membrane ratio was initially somewhat
tion. (Kyle D.J., Osmond C.B. & Arntzen C.J.,
higher than at level 1.
eds.), Elsevier Science Publishers B.V., Amster-
Leaves at level 3 maintained high rates dam, pp. 1-38
uptake throughout the 7 wk period
of 2
C0 Aro E.M., Korhonen P., Rintamaki E. &
under examination (Fig. 2A), although the P. (1985) Diel and seasonal changes
MAenp5d
in the
chloroplast ultrastructure of Des-
quantum flux density decreased markedly
champsia Ilexuosa (L.) Trin. New Phytol. 100,
(Fig. 2B). The thylakoid structure was typi- 537-548
cal of sunny habitats, since the ratio of the
Aro E.M., Rin,[am5ki E., Korhonen P. &
length of appressed to non-appressed thy-
Mienpii P. (1986) Relationship between chlo-
lakoid membranes remained below 1.4
roplast structure and 0 evolution rate of leaf
2
(Fig. 1 B). The leaves examined from discs in plants from different biotopes in south
levels 4 and 5 were physiologically young Finland. Plant Cell Environ. 9. 87-94
and the rates of C0 uptake recorded
2 Boardman N.K. (1977) Comparative photosyn-
were from intermediate to high (Fig. 2A). thesis of sun and shade plants. Annu. Rev.
Plant. Physiol. 2Et, 355-377
The ratio of the length of appressed to
non-appressed thylakoid membranes was, Hudak J. (1981) Plastid 1.
senescence.
of during natural
Changes
however, quite different (Fig. 1 B). One chloroplast structure
in Sinapis alba L.
cotyledons of
senescence
might speculate that the high ratio, 1.5, in
Photosynthetica’15, 174-178
chloroplasts at level 4 was due to the late
Lichtenthaler H.K., Buschmann C., DUI M., Fietz
season, as suggested by Aro et al. (1985).
H.J., Bach T., Kcrzel U., Meier D. & Rahmsdorf
This argument is, however, not valid for U. (1981) Photosynthetic activity, chloroplast
the somewhat younger leaves at level 5, ultrastructure, and leaf characteristics of high-
which had developed under similar clima- and low-light plants and of sun and shade
light
leaves. Photosynth. Res. 2, 115-141
tic conditions but had a lower rate of C02
uptake and an appressed/non-appressed E.M. (1986) Correlation of activity
Vapaavuori
and amount of ribulose 1,5-bisphosphate car-
membrane ratio of about 1.
boxylase with chloroplast stroma crystals in
In the present study, a negative correla- water-stressed willow leaves. J. Exp. Bot. 37,
tion was found between and the ratio
N
P 89-98
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