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Reassessment of the in vivo Assay for Nitrate Reductase in Leaves
Author(s) -
HEUER BRURIA,
PLAUT Z.
Publication year - 1978
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1111/j.1399-3054.1978.tb02583.x
Subject(s) - nitrite , nitrate , nitrate reductase , chemistry , in vivo , biochemistry , nitrite reductase , inorganic chemistry , mannitol , nuclear chemistry , chromatography , biology , organic chemistry , microbiology and biotechnology
The in vivo assay procedure for nitrate reductase and its dependence on the concentration of nitrate and other ions were examined. It was found that high ion concentrations led to an increased release of nitrite to the reaction media which could be interpreted as a stimulated nitrate reductase activity. This phenomenon is not an osmotic effect, since equivalent concentrations of mannitol did not lead to identical results. The effect of ions on the enhanced nitrite production was attributed to changes in cell membrane permeability rather than to a supply of substrate. This conclusion is based on several findings: (a) in in vitro assays, the rate of nitrite production was not affected by ion concentrations: (b) the stimulation of nitrite production was obtained by various ions and not only by nitrate; (c) pretreatment of alfalfa leaves with nitrate did not increase the NO 2 − release rate to the external solution; and (d) nitrate and nitrite export from leaf discs to the solution was stimulated even in discs which were enzymatically inactive. Calcium ions in the presence of KNO 3 inhibited the enhanced nitrite production, probably due to alteration of membrane stability. The effect of ions on the rate of nitrite production was reversible and the high rate of nitrite production was reduced to the control rate when discs were transferred to a solution of low concentration.