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DEVELOPMENT AND HORMONE ACTION

The Control of Storage Xyloglucan Mobilization in Cotyledons of Hymenaea courbaril¹

Seção de Fisiologia e Bioquímica de Plantas, Instituto de Botânica, CEP 01061–970, Sao Paulo, SP, Brazil (H.P.S., M.S.B.); and Departamento de Alimentos e Nutrição Experimental, Faculdade de Ciências Farmacêuticas (E.P.), and Departamento de Botânica, Instituto de Biociências (H.M.), Universidade de Sao Paulo, CEP 05422–970, Sao Paulo, SP, Brazil

Hymenaea courbaril is a leguminous tree species from the neotropical rain forests. Its cotyledons are largely enriched with a storage cell wall polysaccharide (xyloglucan). Studies of cell wall storage polymers have been focused mostly on the mechanisms of their disassembly, whereas the control of their mobilization and the relationship between their metabolism and seedling development is not well understood. Here, we show that xyloglucan mobilization is strictly controlled by the development of first leaves of the seedling, with the start of its degradation occurring after the beginning of eophyll (first leaves) expansion. During the period of storage mobilization, an increase in the levels of xyloglucan hydrolases, starch, and free sugars were observed in the cotyledons. Xyloglucan mobilization was inhibited by shoot excision, darkness, and by treatment with the auxin-transport inhibitor N-1-naphthylphthalamic acid. Analyses of endogenous indole-3-acetic acid in the cotyledons revealed that its increase in concentration is followed by the rise in xyloglucan hydrolase activities, indicating that auxin is directly related to xyloglucan mobilization. Cotyledons detached during xyloglucan mobilization and treated with 2,4-dichlorophenoxyacetic acid showed a similar mobilization rate as in attached cotyledons. This hormonal control is probably essential for the ecophysiological performance of this species in their natural environment since it is the main factor responsible for promoting synchronism between shoot growth and reserve degradation. This is likely to increase the efficiency of carbon reserves utilization by the growing seedling in the understorey light conditions of the rain forest.

² Present address: EMBRAPA Uva e Vinho, Rua Livramento, 515, Caixa Postal 130, CEP 95700–000, Bento Gonçalves, RS, Brazil.

Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.104.040220.

^* Corresponding author; e-mail msbuck{at}usp.br; fax 55 11 50733678.

Received February 1, 2004; returned for revision March 21, 2004; accepted March 23, 2004.

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