title: Dependence of nitrate-induced oxalate accumulation on nitrate reduction in rice leaves.
abstract: Oxalate, a common constituent in many plants, is known to play important functional roles in plants. However, excess levels of oxalate in edible parts of plants adversely affect their quality as food. Understanding the regulatory mechanism in plants, particularly in food crops, is of both scientific and practical significance. While a number of studies have shown that nitrate can efficiently induce oxalate accumulation in plants, how it elicits such an effect is not well understood. This study aimed to gain a further insight into the mechanism underlying the nitrate-induced oxalate accumulation. Nitrate-N efficiently caused oxalate accumulation in rice leaves, depending on the nitrate concentrations and treatment time. In contrast, same nitrogen molar levels of the other N forms such as nitrite, ammonium, glutamate and urea either had no effect on the accumulation or even reduced the oxalate level. When glutamate, glutamine, asparate and asparagine were added into the nutrient solution that already contained saturating concentration of nitrate, both oxalate levels and NR activity were correspondingly decreased. In all of these modes of treatment, the change in NR activity was positively paralleled to that in oxalate levels. For a further confirmation, we generated the transgenic rice plants with a NR interference gene introduced. The result further demonstrated that in the transgenic plants, unlike in wild-type plants, oxalate was no longer able to accumulate in response to the nitrate treatment even though the endogenous nitrate levels were substantially elevated. Taken together, our results suggest that the nitrate-induced oxalate accumulation in rice leaves is dependent on the NR-catalyzed nitrate reduction, rather than on nitrate itself or nitrite reduction or its downstream metabolites.
authors.affiliation: Laboratory of Molecular Plant Physiology, College of Life Sciences, South China Agricultural University, Guangzhou 510642, China.
authors.forename: Hua
authors.initials: H
authors.lastname: Tian
authors.forename: Linrong
authors.initials: L
authors.lastname: Jiang
authors.forename: Ee
authors.initials: E
authors.lastname: Liu
authors.forename: Jianjun
authors.initials: J
authors.lastname: Zhang
authors.forename: Fang
authors.initials: F
authors.lastname: Liu
authors.forename: Xinxiang
authors.initials: X
authors.lastname: Peng
mesh_terms: D000596:Amino Acids / Q000494:pharmacology; D015536:Down-Regulation / Q000187:drug effects; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D050901:Nitrate Reductase / Q000235:genetics / Q000378:metabolism; D009566:Nitrates / Q000378:metabolism* / Q000494:pharmacology*; D009584:Nitrogen / Q000494:pharmacology; D012275:Oryza / Q000187:drug effects* / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D010070:Oxalates / Q000378:metabolism*; D018515:Plant Leaves / Q000187:drug effects* / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D034622:RNA Interference / Q000187:drug effects
chemical_list: D000596:Amino Acids; D009566:Nitrates; D010070:Oxalates; D050901:Nitrate Reductase; D009584:Nitrogen