Research output: Contribution to Journal/Magazine › Journal article › peer-review
Research output: Contribution to Journal/Magazine › Journal article › peer-review
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TY - JOUR
T1 - Nitrate assimilation in the forage legume Lotus japonicus L.
AU - Prosser, Ian M.
AU - Massonneau, Agnes
AU - Smyth, Audra J.
AU - Waterhouse, Rosi N.
AU - Forde, Brian G.
AU - Clarkson, David T.
PY - 2006/3
Y1 - 2006/3
N2 - Nitrate assimilation in the model legume, Lotus japonicus, has been investigated using a variety of approaches. A gene encoding a nitrate-inducible nitrate reductase (NR) has been cloned and appears to be the only NR gene present in the genome. Most of the nitrate reductase activity (NRA) is found in the roots and the plant assimilates the bulk of its nitrogen in that tissue. We calculate that the observed rates of nitrate reduction are compatible with the growth requirement for reduced nitrogen. The NR mRNA, NRA and the nitrate content do not show a strong diurnal rhythm in the roots and assimilation continues during the dark period although export of assimilated N to the shoot is lower during this time. In shoots, the previous low NR activity may be further inactivated during the dark either by a phosphorylation mechanism or due to reduced nitrate flux coincident with a decreased delivery through the transpiration stream. From nitrate-sufficient conditions, the removal of nitrate from the external medium causes a rapid drop in hydraulic conductivity and a decline in nitrate and reduced-N export. Root nitrate content, NR and nitrate transporter (NRT2) mRNA decline over a period of 2 days to barely detectable levels. On resupply, a coordinated increase of NR and NRT2 mRNA, and NRA is seen within hours.
AB - Nitrate assimilation in the model legume, Lotus japonicus, has been investigated using a variety of approaches. A gene encoding a nitrate-inducible nitrate reductase (NR) has been cloned and appears to be the only NR gene present in the genome. Most of the nitrate reductase activity (NRA) is found in the roots and the plant assimilates the bulk of its nitrogen in that tissue. We calculate that the observed rates of nitrate reduction are compatible with the growth requirement for reduced nitrogen. The NR mRNA, NRA and the nitrate content do not show a strong diurnal rhythm in the roots and assimilation continues during the dark period although export of assimilated N to the shoot is lower during this time. In shoots, the previous low NR activity may be further inactivated during the dark either by a phosphorylation mechanism or due to reduced nitrate flux coincident with a decreased delivery through the transpiration stream. From nitrate-sufficient conditions, the removal of nitrate from the external medium causes a rapid drop in hydraulic conductivity and a decline in nitrate and reduced-N export. Root nitrate content, NR and nitrate transporter (NRT2) mRNA decline over a period of 2 days to barely detectable levels. On resupply, a coordinated increase of NR and NRT2 mRNA, and NRA is seen within hours.
KW - Diurnal - Legume - Lotus - Nitrate assimilation - Nitrate reductase - Nutrient deprivation
U2 - 10.1007/s00425-005-0124-9
DO - 10.1007/s00425-005-0124-9
M3 - Journal article
VL - 223
SP - 821
EP - 834
JO - Planta
JF - Planta
SN - 0032-0935
IS - 4
ER -