Gene expression of lactate dehydrogenase and alcohol dehydrogenase under anaerobic conditions

在厌氧条件下，三羧酸途径被阻断，丙酮酸通过乳酸和乙醇发酵代谢。我们分析了这两种发酵途径的关键酶乙醇脱氢酶（ADH）和乳酸脱氢酶（LDH）的基因表达。ADH(1)在ADH活性降低的突变体（rad）中，由于NAD的减少，果糖1,6 -二磷酸积累。(2) ADH活性定位于根，突变体中仅观察到ADH2单二聚体的同工酶带。(3)未观察到ADH1同工酶带，但ADH1 mRNA正常产生。(4)突变体的耐淹性低于野生型，说明抗旱性对水稻幼苗的耐淹性有重要影响。(1)克隆LDH基因并测序。通过5′-RACE法确定转录起始点为ATG的-129。基因组南杂交结果表明，水稻LDH基因为单拷贝，不同于动物和大麦的LDH基因。(2)无氧条件下LDH mRNA水平连续升高6 h后逐渐下降。水稻中LDH mRNA在厌氧条件下的诱导时间比大麦和玉米中的ADH和LDH更短暂。(3)通过RFLP分析，将水稻LDH基因定位在6号染色体上。

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.