Relationship between the structural and functional changes of the photosynthetic apparatus during chloroplast-chromoplast transition in flower bud of Lilium longiflorum
Relationship Between the Structural and Functional Changes of the Photosynthetic Apparatus During Chloroplast-Chromoplast Transition in Flower Bud of Lilium longiflorum(para)
The relationship between the structural and functional changes of the photosynthetic apparatus in the flower bud of Lilium longiflorum during chloroplast-chromoplast transition was examined. Compared with green petals, there was a five-fold increase of the carotenoid content in yellow petals, whereas the chlorophyll content decreased five-fold. Absorption and emission fluorescence spectra of chromoplasts indicated that newly synthesized carotenoids were not associated with photosystem II (PSII) photochemistry. The maximum quantum yield in the remaining PSII reaction centers remained constant during the chromoplast formation, whereas the photosynthetic electron transport beyond PSII became inhibited, as indicated by a marked decrease of the O^sub 2^ evolution capacity, of the photochemical quenching of chlorophyll-a fluorescence and of the operational quantum yield of photosynthetic electron transport. Deconvoluted fluorescence emission spectra indicated a more rapid degradation of photosystem I (PSI) complexes than of PSII during chromoplast formation. Compared with green petals, the spillover between PSII and PSI decreased by approximately 40% in yellow petals. Our results indicate that during chloroplast-chromoplast transition in the flower bud of L. longiflorum, PSII integrity was preserved longer than the rest of the photosynthetic apparatus.
Abbreviations: CC, core complex; CP, chlorophyll-protein complex; LHC, light-harvesting complex; PSI, photosystem I; PSII, photosystem II; Q^sub A^, primary quinone electron acceptor of PSII; Q^sub N^, nonphotochemical quenching; Q^sub P^, photochemical quenching; Phi^sub M^, maximal PSII quantum yield; Phi’M, operational PSII quantum yield.
Flower development involves several physiological and ultrastructural changes, namely, the transition from chloroplasts to chromoplasts manifested by typical color changes of petals or sepals (or both) (1,2). During this transition the chloroplast loses its photosynthetic activity and its chlorophyll content while it accumulates large amounts of carotenoids whose vivid colors attract animals and thereby favor pollination (1,3). During the chloroplasts to chromoplasts transition the gradual replacement of the thylakoid membranes by a chlorophyll-free and unstacked lamellae system is consistent with the degradation of the light-harvesting chlorophyll-protein complexes (CP) (LHCII proteins) associated with photosystem II (PSII) (4,5). There is evidence that electron transport carriers, such as plastocyanine and Ferredoxine-NADP-oxidoreductase, also diminish during the chloroplast-chromoplast transition, as it was found in tomato fruit pericarps (4).
In a more recent study Clement et al. (6) observed that during the development of Lilium longiflorum flower buds the reduction of chlorophyll content and the loss of thylakoid integrity occurred well after the rapid decline of photosynthetic activity. This decline was associated with a stomatal limitation occurring during the chloroplast-chromoplast transition. Therefore, the relationship between the structural and functional changes of the photosynthetic apparatus during the chloroplast-chromoplast transition in the flower bud of L. longiflorum is not yet clearly established.
In this report we present a detailed spectroscopic analysis of the changes of photosynthetic pigments associated with both PSII and photosystem I (PSI) and the modification of the energy distribution between these two photosystems that occurred during the chloroplast-chromoplast transition in developing Lilium petals. We then referred these findings to the changes of photosynthetic activity and efficiency. Our results indicated that the PSII complexes are less affected than the PSI complexes during the chloroplast-chromoplast transition. This may explain why the PSII activity is relatively more stable than the overall photosynthetic electron transport during chromoplast formation.
Acknowledgements-This work was supported by operating grants of the Natural Science and Engineering Research Council (NSERC) of Canada and by a FCAR-Equipe grant awarded to R.P. and G.S. PT was supported by an FCAR fellowship.[Posted on the web site on March 4, 2002.
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Philippe Juneau1, Pascaline Le Lay1, Bela Boddi2, Guy Samson3 and Radovan Popovic*1
1Departement de Chimie-Biochimie/TOXEN-Centre de Recherche en Toxicologie Environnementale, Universite du Quebec a Montreal, Montreal, Quebec, Canada;
2Department of Plant Anatomy, Eotvos, Budapest, Hungary and
3Departement de Chimie-Biologie, Universite du Quebec a Trois-Rivieres, Trois-Rivieres, Quebec, Canada
Received 5 October 2001; accepted 7 January 2002
*To whom correspondence should be addressed at: Departement de Chimie-Biochimie/TOXEN-Centre de Recherche en Toxicologie Environnementale, Universite du Quebec a Montreal, 2101 Jeanne-Mance, Montreal, Quebec. Canada H2X 2J6. Fax: 514– 987-4054: e-mail: email@example.com
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