RESUMO
Dormant seeds do not germinate when imbibed in water even when conditions are favorable for germination. These hydrated seeds remain viable, but growth-arrested for weeks due to unknown restrictions within the embryo. As a model system for the study of the molecular processes occurring in dormant seeds, we have chosen to examine gene expression in Bromus secalinas, a grass species that produces seeds with high levels of embryonic dormancy. Using differential screening for mRNAs present in hydrated dormant embryos, we have identified a cDNA clone, pBS128, that encodes a mRNA transcript found in the embryos of hydrated seeds of B. secalinus as well as in embryos from mature dry seeds. Striking differences in pBS128 transcript levels appear upon hydration of dormant and nondormant seeds. Upon imbibition pBS128 transcript levels increase over four-fold in dormant seeds, but rapidly decline and disappear in nondormant seeds, which subsequently germinate. The pBS128 transcript appears to be embryo-specific since the transcript is not detectable in either non-stressed or dehydrated seedling tissue. Application of 50 microM ABA to nondormant seeds arrests germination and enhances pBS128 transcript levels. The nucleotide sequence of the nearly full-length pBS128 cDNA shows no homology to other reported genes, and the putative protein sequence does not exhibit the hydrophilic characteristics of the ABA-responsive LEA (late embryogenesis abundant) proteins.
Assuntos
Plantas/genética , RNA Mensageiro/metabolismo , Sementes/fisiologia , Ácido Abscísico/metabolismo , Sequência de Aminoácidos , Sequência de Bases , Northern Blotting , Clonagem Molecular , DNA/genética , DNA/isolamento & purificação , Biblioteca Gênica , Cinética , Dados de Sequência Molecular , Fenômenos Fisiológicos Vegetais , Plasmídeos , RNA/genética , RNA/isolamento & purificação , RNA Mensageiro/genética , Transcrição GênicaRESUMO
Hydrated dormant cereal seeds do not germinate even when environmental conditions are favorable for germination. By using cDNA cloning and differential screening, we have identified mRNAs from five gene families that are abundant in the embryos of imbibed, but developmentally arrested wheat (Triticum aestivum L.) seeds. Gene transcript levels of these mRNAs are maintained and even increase in embryos of imbibed dormant seeds for as long as the seeds remain dormant. In contrast, transcript levels decline in nondormant seeds after imbibition and disappear as germination occurs. All the identified genes are ABA responsive. Based on these data we conclude that wheat seeds in the hydrated dormant state exhibit prolonged expression of ABA-responsive genes.
Assuntos
Desoxirribonucleases , Escherichia coli/enzimologia , Adenosina Trifosfatases , Trifosfato de Adenosina , Ligação Competitiva , Fenômenos Químicos , Química , DNA/efeitos da radiação , Replicação do DNA , DNA Bacteriano , DNA Circular , DNA de Cadeia Simples , Exonucleases , Cinética , Mutação , Conformação de Ácido Nucleico , Desnaturação de Ácido Nucleico , Hibridização de Ácido Nucleico , Pâncreas/enzimologia , Isótopos de Fósforo , RNA , Efeitos da Radiação , Relação Estrutura-Atividade , Trítio , Raios UltravioletaAssuntos
Desoxirribonucleases/isolamento & purificação , Escherichia coli/enzimologia , Trifosfato de Adenosina , Sulfato de Amônio , Sequência de Bases , Centrifugação com Gradiente de Concentração , Cromatografia DEAE-Celulose , Cromatografia em Gel , Cromatografia por Troca Iônica , Cromatografia em Camada Fina , DNA Bacteriano , DNA de Cadeia Simples , DNA Viral , Desoxirribonucleases/análise , Eletroforese , Peso Molecular , Mutação , Desnaturação de Ácido Nucleico , Peptídeos/análise , Isótopos de Fósforo , Fosfotransferases , Polinucleotídeos , Estreptomicina , Relação Estrutura-Atividade , TrítioRESUMO
A new endonuclease activity from Escherichia coli which cleaves circular, single-stranded DNA in the presence of added nucleoside triphosphate has been purified. The activity has not been detected in extracts from certain rec(-) strains and is therefore implicated in genetic recombination.