Báo cáo khoa học: "Comparison between the structure and function of chloroplasts at different levels of willow canopy during a growing season"

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Nội dung Text: Báo cáo khoa học: "Comparison between the structure and function of chloroplasts at different levels of willow canopy during a growing season"

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