DIFFERENTIAL INDUCTION OF PYRUVATE DECARBOXYLASE SUBUNITS AND TRANSCRIPTS IN ANOXIC RICE SEEDLINGS

In 2-d-old rice (Oryza sativa L.) seedlings subjected to anoxic stress , pyruvate decarboxylase (PDC) activity increased 9-fold during a 168- h period. A polyclonal PDC antiserum that recognized alpha- and beta-s ubunits was used to quantify PDC protein by an enzyme-linked immunosor bant assay and showed a 5.6-fold increase, suggesting that the anoxica lly induced enzyme has a higher specific activity than the PDC isoform present under normoxia. Immunoblot analysis showed that levels of bot h PDC subunits were induced by anoxia. Immunoprecipitation of proteins labeled in vivo during anoxic treatment demonstrated that the alpha-s ubunit was preferentially synthesized at the onset of anoxia. Two part ial cDNAs, including a novel sequence, were cloned from a cDNA library made from seedlings subjected to anoxia for 6 h. Gene-specific probes used to quantify northern blots showed that two or three PDC mRNAs ar e differentially induced by anoxia in rice seedlings. Immunoprecipitat ion of in vitro translation products of mRNAs isolated at different ti mes of anoxic treatment confirmed this finding. Our results suggest th at anoxic induction of rice PDC involves transcriptional and posttrans criptional regulation of gene expression as well as differences in enz yme characteristics.