Differential regulatory role of nitric oxide in mediating nitrate reductase activity in roots of tomato (Solanum lycocarpum).
OBJECTIVE
Nitric oxide (NO) has been demonstrated to stimulate the activity of nitrate reductase (NR) in plant roots supplied with a low level of nitrate, and to affect proteins differently, depending on the ratio of NO to the level of protein. Nitrate has been suggested to regulate the level of NO in plants. This present study examined interactive effects of NO and nitrate level on NR activity in roots of tomato (Solanum lycocarpum).


METHODS
NR activity, mRNA level of NR gene and concentration of NR protein in roots fed with 0.5 mM or 5 mM nitrate and treated with the NO donors, sodium nitroprusside (SNP) and diethylamine NONOate sodium (NONOate), and the NO scavenger, 2-(4-carboxyphenyl)-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide (cPTIO), were measured in 25-d-old seedlings.


RESULTS
Addition of SNP and NONOate enhanced but cPTIO decreased NR activity in the roots fed with 0.5 mm nitrate. The opposite was true for the roots fed with 5 mM nitrate. However, the mRNA level of the NR gene and the protein concentration of NR enzyme in the roots were not affected by SNP treatment, irrespective of nitrate pre-treatment. Nevertheless, a low rate of NO gas increased while cPTIO decreased the NR activities of the enzyme extracts from the roots at both nitrate levels. Increasing the rate of NO gas further increased NR activity in the enzyme extracts of the roots fed with 0.5 mM nitrate but decreased it when 5 mM nitrate was supplied. Interestingly, the stimulative effect of NO gas on NR activity could be reversed by NO removal through N(2) flushing in the enzyme extracts from the roots fed with 0.5 mM nitrate but not from those with 5 mM nitrate.


CONCLUSIONS
The effects of NO on NR activity in tomato roots depend on levels of nitrate supply, and probably result from direct interactions between NO and NR protein.
Ministry of Education Key Laboratory of Environmental Remediation and Ecosystem Health, College of Natural Resources and Environmental Science, Zhejiang University, Hangzhou, China.
Chong Wei
CW
Jin
Shao Ting
ST
Du
Yong Song
YS
Zhang
Xian Yong
XY
Lin
Cai Xian
CX
Tang
D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D006834:Hydrazines / Q000494:pharmacology; D018551:Solanum lycopersicum / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D050901:Nitrate Reductase / Q000235:genetics / Q000378:metabolism*; D009566:Nitrates / Q000494:pharmacology; D009569:Nitric Oxide / Q000378:metabolism*; D020030:Nitric Oxide Donors / Q000494:pharmacology; D009599:Nitroprusside / Q000494:pharmacology; D018517:Plant Roots / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*
D006834:Hydrazines; D009566:Nitrates; D020030:Nitric Oxide Donors; D009599:Nitroprusside; D009569:Nitric Oxide; C084012:1,1-diethyl-2-hydroxy-2-nitrosohydrazine; D050901:Nitrate Reductase