open access

https://hdl.handle.net/2115/64675

Nitrate reductase as a producer of nitric oxide in plants : temperature-dependence of the enzymatic active nitrogen formation

英語

temperature stress

2001

CSIRO

(S21-003)

Nitric oxide (NO) has long been recognized as a harmful air pollutant that can be produced through industrial activities. After the discovery of NO synthase (NOS, EC 1.14.13.39) that produces NO during the conversion of L-arginine to L-citrulline, our view of NO has been drastically changed from a harmful pollutant to an important signal messenger in animal cells (Yamasaki, 2000). In contrast to the large body of knowledge on functions of NO in animal systems, however, little is known in plant systems. Recent studies have suggested that NO is involved in a broad spectrum of physiological responses, including pathogen response, programmed cell death, germination, phytoalexin production and ethylene emission (Bolwell, 1999; Wendehenne, 2001). Although NOS inhibitor experiments using N-nitro-L-arginine (L-NNA), NG-monomethyl-L-arginine (L-NMMA) or NG-nitro-L-arigine-methyl ester (L-NAME) have suggested the existence of a mammalian-type NOS in plants, no plant NOS gene has been conclusively identified to date. Furthermore, no homologue of mammalian-type NOS has been found in the genome of Arabidopsis thaliana. Thus, the presence of mammalian-type NOS in plants remains a subject to be clarified and the mechanism for NO production in plant cells has not yet been confirmed. It has been sometimes reported that several plant and algal species emit NO when nitrate or nitrite is supplied in darkness. In the legume plant Glycine max, the constitutive nitrate reductase (cNR) was identified to produce NO (Dean and Harper, 1986). Harper and coworkers have suggested that NO would be produced from nitrite by the activity of cNR (Dean and Harper, 1988). Normally, NR is the rate-limiting step enzyme of nitrate assimilation in plants and algae, catalyzing the reduction of nitrate (NO3-) to nitrite (NO2-). The NO producing activity had been considered a unique characteristic of cNR that is only distributed in the Phaseolus tribe of the family leguminosae (Dean and Harper, 1988). We have recently shown in vitro evidence that maize inducible NR (iNR) is also capable of producing NO though one electron reduction of nitrite (Yamasaki et al., 1999). A similar nitrite-dependent NO production catalyzed by NR has been reported in bacteria and fungi (Yamasaki, 2000). These results suggest that NO producing acitivity of NR is a more general feature than was previously thought (Yamasaki, 2000). Here we demonstrate that production of active nitrogen species (NO and ONOO-) by NR is strongly temperature-dependent.

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