Functional analysis of lactate dehydrogenase during hypoxic stress in Arabidopsis

During waterlogging conditions plants switch from aerobic respiration to anaerobic fermentation to cope with the lack of available oxygen. Plants have two main fermentation pathways: ethanol and lactic acid fermentation. In this paper we carry out a functional analysis of the Arabidopsis lactate dehydrogenase gene, LDH1. Our results indicate that LDH1, like some other anaerobic genes, is expressed in a root-specific manner and is affected by a variety of abiotic stresses (hypoxia, drought, cold) and mechanical wounding. Functional analysis of LDH1 was carried out using transgenic Arabidopsis overexpressing the gene (35S promoter) and a T-DNA knockout line. Overexpression of LDH1 resulted in improved survival of low oxygen stress conditions in roots but not in shoots. Increased lactic acid fermentation also resulted in significantly higher activities of pyruvate decarboxylase (PDC). Knockout mutants of LDH1 showed reduced survival under low oxygen conditions and PDC activity levels were not changed compared with the wild type. Our data suggest that there is an interdependency between the lactic and ethanol fermentation pathways and that lactic acid fermentation may play a role in stimulating ethanol fermentation and improving plant survival. We show also that Arabidopsis plants are able to exude lactate efficiently into the medium, preventing it accumulating to toxic levels in the cells.