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POLISSACARÍDEOS DE RESERVA DE PAREDE CELULAR EM SEMENTES. ESTRUTURA, METABOLISMO, FUNÇÕES E ASPECTOS ECOLÓGICOS1

01/2000;

ABSTRACT RESUMO - Entre os principais polissacarídeos de reserva em plantas estão o amido, os frutanos e os polissacarídeos de reserva de parede celular. Estes últimos ocorrem principalmente em sementes e podem ser classificados de acordo com suas estruturas químicas em mananos, xiloglucanos e galactanos. Apesar das diferenças marcantes nas estruturas químicas, os polímeros dos três grupos apresentam propriedades físico-químicas semelhantes. Eles possuem em comum a função de reserva, uma vez que são completamente degradados após a germinação da semente e seus produtos são utilizados como fontes de carbono e energia para o crescimento inicial das plântulas. Por outro lado, cada um deles apresenta funções secundárias tais como o controle da embebição e distribuição de água nos tecidos das sementes e o controle da expansão celular dos cotilédones. Na presente revisão, apresentamos uma atualização sobre as estruturas químicas, ocorrência e metabolismo desses polissacarídeos em sementes. São discutidos alguns pontos de controle de sua deposição e mobilização, bem como suas funções biológicas e papéis ecológicos. Estes aspectos são abordados com ênfase nos possíveis mecanismos evolutivos que levaram às alterações nas relações estrutura-função nas paredes celulares primárias de plantas superiores e ao surgimento das paredes de reserva. TERMOS ADICIONAIS PARA INDEXAÇÃO: Parede celular, polissacarídeos, reserva, sementes,

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