Nitrate reduction cytoplast chloroplast CYTOPLASM CHLOROPLAST the e reduction of reduction of Phospho Triosephosphate NO to NO..glycerate NO2 to NH3 This requires This NAD t the enzyme requires the NADH nitrate enzyme Ferredoxin reductase nitrite 6H 力20 ductase 6e H 2 H20 Nitrate reduction Nitrite reduction
Nitrate reduction cytoplast Step 1 – the reduction of NO3 - to NO2 - . This requires the enzyme nitrate reductase. Step 2 – the reduction of NO2 - to NH3 . This requires the enzyme nitrite reductase. chloroplast
Prosthetic groups辅基 of the nitrate reductase and sequence of reactions(Guererro et al. 1981) NAD(P)H+H+ FAD 2Cytochr. b-Fell Moy NO2+H2O NAD(P) FADH2 2 Cytochr.b-Fe厘 NO Phrosthetic groups of the nitrate reductase and the sequence of reactions(according to GUERRERo er al. [1981D). NAD(P)H denotes that both coenzymes NADH and NADPH may function as H donors
Prosthetic groups辅基 of the nitrate reductase and sequence of reactions (Guererro et al. 1981)
The characteristics of Nr and its regulation Nitrate induced the synthesis of mRNA coding for NR The turn over of Nr is rapid Light play an important role in nitrate assimilation owing to lack of reducing power in night The assimilation of nitrate by plants is influenced by plant nutrition and in particular by Mo The activity of the Nr is rapidly modulated by environmental conditions, such as light intensity, Co2 concentration and oxygen supply
The characteristics of NR and its regulation ▪ Nitrate induced the synthesis of mRNA coding for NR ▪ The turn over of NR is rapid ▪ Light play an important role in nitrate assimilation owing to lack of reducing power in night. ▪ The assimilation of nitrate by plants is influenced by plant nutrition and in particular by Mo. ▪ The activity of the NR is rapidly modulated by environmental conditions, such as light intensity, CO2 concentration and oxygen supply
Nitrate reductase activity in maize roots after an exposure of young plants to nutrient solutions containing NO3, NH4, or NHANO3 ( Mengel et al 1985) Treatment R activity, u mol NO2/hXg fresh weight NH4 0.10a NhNO3 095b nO3 3.71c
Nitrate reductase activity in maize roots after an exposure of young plants to nutrient solutions containing NO3 - , NH4 + , or NH4NO3 (Mengel et al 1985) Treatment NR activity, μmol NO2 - /h×g fresh weight NH4 + 0.10a NH4NO3 0.95b NO3 - 3.71c
Effect of time of day on the nitrate concentration of spinach(SteingrOver 1982) stems leaf Petiole Time of day Mg No3-N/kg fresh matter 8:30 372 830 13:30 207 101 546 17:30 189 504
Effect of time of day on the nitrate concentration of spinach (SteingrÖver 1982) stems leaf Petiole Time of day Mg NO3 - -N/kg fresh matter 8:30 372 228 830 13:30 207 101 546 17:30 189 91 504