Gene expression of lactate dehydrogenase and alcohol dehydrogenase under anaerobic conditions

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Under anaerobic condition, the tricarboxylic pathway is blocked and pyruvate is metabolized via lactate and ethanol fermentation. We have analyzed the gene expression of alcohol dehydrogenase (ADH) and lactate dehydrogenase (LDH) which are the key enzumes of these two fermentation pathway.1.ADH(1) In a mutant with reduced ADH activity (rad) , fructose 1,6 bis phosphate was accumulated due to reduced amount of NAD.(2) ADH activity was localized in root and only the isozume band for ADH2 mono-dimer was observed in the mutant. (3) mRNA of ADH1 was normally produced although no isozyme band for ADH1 was obserbed. (4) The submergence tolerance of the mutant was inferior to wild type suggesting that ADH is important for submergence tolerance of the rice seedlings.2.LDH(1)A gene for LDH was cloned and sequenced. The transcription start point was determined to be -129 from ATG by 5'-RACE method. Result of genomic southern hybridization suggested that the LDH gene is single copy in the rice genome, which differ from the LDH gene of animal and barley. (2) The level of LDH mRNA increased continuously for six hours then declined gradually under anaerobic condition. LDH mRNA in rice is induced more transiently in response to anaerobic than ADH and LDH in barley and maize.(3) The rice LDH gene was mapped on chromosome 6 by RFLP analysis.