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Change in Nitrate-Reducing Activity in Squash Seedlings with NO2 Fumigation |
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| Authors: | Takeuchi Yuichi; Nihira Junko; Kondo Noriaki; Tezuka Takafumi |
| Institution: | 1 Division of Environmental Biology, The National Institute for Environmental Studies Yatabe-machi, Tsukuba, Ibaraki 305, Japan 2 The Graduate School of Environmental Science, The University of Tsukuba Sakura-mura, Niihari, Ibaraki 305, Japan 3 Laboratory of Horticultural Science, Faculty of Agriculture, Nagoya University Nagoya 464, Japan |
| Abstract: | Nitrogen dioxide (NO2) fumigation inhibited nitrate reductase(NR, EC 1.6.6.1 EC] ) activity assayed by an in vivo system in thecotyledons, but not in the first leaves, of squash (Cucurbitamaxima Duch.) seedlings. The inhibition was recovered when theseedlings were transferred to NO2-free conditions, indicatingthat the effect of NO2 was reversible. The NADH content in thecotyledons, photosynthetic O2 evolution and respiratory O2 uptakedid not change notably under NO2 fumigation. Nitrate contentsin the cotyledons and first leaves did not change with NO2 fumigation,but nitrite, ammonium and rapidly-metabolized amino acids contentsincreased. The inhibitory effect of NO2 was also observed inthe in vitro assay, though the inhibition rate was smaller thanthat in the in vivo assay. These results indicate that the inhibitoryeffect of NO2 on NR activity in squash cotyledons was derivedin part from the decrease in the amount of active NR due toammonium and/or amino acids accumulated in the tissue underNO2 fumigation. (Received February 12, 1985; Accepted May 27, 1985) |
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