AOBPreview originally published online on October 28, 2004
Annals of Botany 2004 94(6):819-830; doi:10.1093/aob/mch209
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Annals of Botany 94/6, © Annals of Botany Company 2004; all rights reserved
The Role of the Storage Carbon of Cotyledons in the Establishment of Seedlings of Hymenaea courbaril Under Different Light Conditions
1 EMBRAPA Uva e Vinho. Rua Livramento, 515, Caixa Postal 130, CEP 95700-000, Bento Gonçalves, RS, Brazil and 2 Seção de Fisiologia e Bioquímica de Plantas, Instituto de Botânica, C. Postal 4005, CEP 01061-970, São Paulo, SP Brazil
* For correspondence. E-mail msbuck{at}usp.br
Received: 4 March 2004 Returned for revision: 27 April 2004 Accepted: 20 August 2004 Published electronically: 28 October 2004
• Background and Aims Hymenaea courbaril (Leguminosae-Caesalpinioideae) is a tree species with wide distribution through all of the Neotropics. It has large seeds (approx. 5 g) with non-photosynthetic storage cotyledons rich (40 %) in a cell wall polysaccharide (xyloglucan) as a carbon reserve. Because it is found in the understorey of tropical forests, it has been considered as a shade-tolerant, late-secondary species. However, the physiological mechanisms involved in seedling establishment, especially regarding the interplay between storage and light intensity, are not understood. In this work, the ecophysiological role of this carbon cotyledon reserve (xyloglucan) is characterized, emphasizing its effects on seedling growth and development during the transition from heterotrophy to autotrophy under different light conditions.
• Methods Seedlings of H. courbaril were grown in environments with different light intensities, and with or without cotyledons detached before xyloglucan mobilization. Development, growth, photosynthesis and carbon partitioning (dry mass and [14C]sucrose) were analysed in each treatment.
• Key Results The detachment of cotyledons was not important for seedling survival, but resulted in a strong restriction (50 % less) of shoot growth, which was the main sink for the cotyledon carbon reserves. Carbon restriction promoted an early maturation of the photosynthetic apparatus without changes in the net CO2 fixation per unit area. The reduced surface area of the first leaves in seedlings without cotyledons was evidence of limited growth and development of seedlings in low light conditions (22 µmol m–2 s–1 photon flux).
• Conclusions There is an increase in the importance of storage xyloglucan in cotyledons for H. courbaril seedling development as light intensity decreases, confirming that this polymer plays a key role in the adaptation of this species to establish successfully in the shadowed understorey of the forest.
Key words: Carbon partitioning, forest, light, growth, cell wall, Hymenaea courbaril, photosynthesis, seedling, xyloglucan, storage
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