TEMPORAL AND SPATIAL COEXPRESSION OF HYDROGENASE AND NITROGENASE GENES FROM RHIZOBIUM-LEGUMINOSARUM BV VICIAE IN PEA (PISUM-SATIVUM L) ROOT-NODULES

Expression of the Rhizobium leguminosarum bv. viciae hydrogen uptake ( hup) genes in pea root nodules has been studied by in situ hybridizati on. Accumulation of transcripts specific for the hydrogenase structura l genes (hupSL) abruptly started at the beginning of the interzone II- III and continued throughout the nitrogen-fixing zone III. This accumu lation paralleled that of nifA- and nifH-specific mRNAs, and hupSL mRN As were detected in the same cells as nif mRNAs. This suggests that th e signals or regulators that trigger nitrogenase expression in nodules are also responsible for hydrogenase induction. Mutations in several hydrogenase accessory genes did not affect the pattern of hupSL expres sion, suggesting that these genes are not involved in hydrogenase regu lation.