不同品种菠菜叶肉及叶柄中硝态氮累积与硝酸还原酶活性的关系

盆栽试验条件下,菠菜体内的硝态氮含量及硝酸还原酶(NR)活性因品种和部位而异。硝态氮含量以短缩茎中最高,叶和叶柄中次之,根中最低,且根/冠比越大的品种,其整体植株中的硝态氮含量越低;根尤其是侧根NR活性较高;叶肉和叶柄中硝态氮含量均与根中以内、外源硝酸盐为底物的NR活性呈一定的负相关。

Nitrate reductase activity and its diurnal variation rhythm for Camptotheca acuminata seedlings

Nitrate reductase activity (NRA) in different plant organs and leaves in different positions of Camptotheca acuminata seedlings was determined by an In vivo assay, the diurnal variation rhythm of NRA in leaves of different positions was observed,and the correlations between leaf NRA, leaf area and lamina mass per unit area (LMA) were also examined. The results showed that NRA in the leaf was significantly highest, compared with that in other organs such as roots, stems and leaves. In this experiment, the 10 leaves were selected from the apex to the base of the seedlings in order. The different NRA occurred obviously in leaves of different positions of C. acuminata seedlings from the apex to the base, and NRA was higher in the 4th-6th leaves.The diurnal change rhythm of leaf NRA showed a one peak curve, and maximum NRA value appeared at about midday (at 12:30 or so). No obvious correlations between NRA and leaf area or lamina mass per unit area were observed. This study offered scientific foundation for the further research on nitrogen metabolism of C. acuminata.

Dynamic Changes of Nitrate Reductase Activity within 24 Hours

[Objective] The research aimed to study the circadian rhythm of nitrate re- ductase activity （NRA） in plant. [Method] The wheat plants at heading stage were used as the materials for the measurement of dynamic changes of nitrate reductase activity （NRA） within 24 h under the conditions of constant high temperature. [Resulti The fluctuation of NRA in wheat changed greatly from 20：00 pm to 11：00 am. The enzyme activity remained constant, but at 14：00 the enzyme activity was the high- est, higher than all the other time points except the enzyme activity measured at11：00. The enzyme activity was the lowest of 17：00, which was lower than all the other time points except the enzyme activity measured at 2：00. [Conclusion] There were autonomous rhythm changes of NRA in wheat in a certain degree.

Effects of elevated CO_2 on the photosynthesis and nitrate reductase activity of Pyropia haitanensis(Bangiales,Rhodophyta) grown at different nutrient levels

Pyropia haitanensis, a commercially important species, was cultured at two CO2 concentrations （390× 10^-6 and 700× 10^-6 （parts per million）） and at low and high nutrient levels, to explore the effect of elevated CO2 on the species under nutrient enrichment. Results show that in CO2-enriched thalli, relative growth rate （RGR） was enhanced under nutrient enrichment. Elevated CO2 decreased phycobiliprotein （PB） contents, but increased the contents of soluble carbohydrates. Nutrient enrichment increased the contents of chlorophyll a （Chl a） and PB, while soluble carbohydrate content decreased. CO2 enrichment enhanced the relative maximum electronic transport rate and light saturation point. In nutrient-enriched thalli the activity of nitrate reductase （NRA） increased under elevated CO2. An instantaneous pH change in seawater （from 8.1 to 9.6） resulted in reduction of NRA, and the thalli grown under both elevated CO2 and nutrient enrichment exhibited less pronounced reduction than in algae grown at the ambient CO2. The thermal optima of NRA under elevated CO2 and/or nutrient enrichment shifted to a lower temperature （10-15 ℃） compared to that in ambient conditions （20℃）. We propose that accelerated photosynthesis could result in growth increment. N assimilation remained high in acidified seawater and reflected increased temperature sensitivity in response to elevated CO_2 and eutrophication.

Metabolic Plasticity of Nitrogen Assimilation by Porphyra umbilicalis(Linnaeus) Kützing

The physical stresses associated with emersion have long been considered major factors determining the vertical zona- tion of intertidal seaweeds. We examined Porphyra umbilicalis （Linnaeus） Kiitzing thalli from the vertical extremes in elevation of an intertidal population （i.e. upper and lower intertidal zones） to determine whether Porphyra thalli acclimate to different vertical elevations on the shore with different patterns of nitrate uptake and nitrate reductase （NR） and glutamine synthetase （GS） activities in response to different degrees of emersion stress. We found that the nitrate uptake and NR recovery in the emersed tissues took longer in lower intertidal sub-population than in upper intertidal sub-population; and GS activity was also significantly affected by emersion and, interestingly, such an activity was enhanced by emersion of thalli from both upper and lower intertidal zones. These results sug- gested that intta-population variability in post-emersion recovery of physiological functions such as nutrient uptake and NR activity enables local adaptation and contributes to the wide vertical distribution ofP. umbilicalis. The high GS activity during periodic emer- sion stress may be a protective mechanism enabling P umbilicalis to assimilate nitrogen quickly when it again becomes available, and may also be an evidence ofphotorespiration during emersion.

Growth and Quality of Chinese Kale Grown Under Different LEDs

[Objective] This study was conducted to investigate the effects of light quality on growth and quality of Chinese kale(Brassica alboglabra Bailey). [Method]Chinese kale was grown in hydroponic under three different Light Emitting Diode(LEDs) conditions [red∶blue=8∶1(8R1B), red∶blue=6∶3(6R3B) and red∶green∶blue=6∶2∶1(6R2G1B), 12 h light, 50 μmol/(m2·s)]. Then its growth and quality indices including root and shoot fresh weight and dry weight, concentrations of soluble protein, vitamin C, nitrate, soluble phenols, flavonoids, soluble sugar, free amino acids, and activity of nitrate reductase were measured. [Result] There was no significant difference in plant height, diameter of flower stalk and leaf number among three LED treatments. The fresh weight of shoot, root and plant in 8R1 B and 6R2G1 B was significantly higher than in 6R3 B. The dry weight of shoot and plant in 8R1 B was significantly higher than in 6R3 B. The concentrations of vitamin C, soluble protein and soluble sugar in flower stalk of 6R3 B treatment were significantly higher than those in 8R1 B and 6R2G1 B, while there was no remarkable difference in concentrations of reducing sugar, soluble phenol, flavonoids and free amino acid among the three treatments. The nitrate concentration in flower stalk of 6R3 B was significantly lower than in the other two treatments, and the activity of nitrate reductase in6R3 B was significantly higher than in the other two treatments. [Conclusion] The LED treatment of red:blue=6:3 was more suitable for the growth of Chinese kale.

Effects of Nitrogen Sources on Nitrate Reductase Activity and Some Physiological Parameters in Psyllium （Plantago ovata F.） under Salinity Stress

The effects of three nitrogen sources （ammonium, nitrate and ammonium＋nitrate） and three salt treatments （0, 100 and 200 mM NaCl） on nitrate reductase activity, proline, soluble protein and carbohydrate contents in psylliom （Plantago ovata） plants were Studied. The nitrate reductase activity tended to increase when NO3- was included in the root-zone solution, but decrease as salinity increased. All N sources stimulated plant growth and nutrient uptake. Shoot and root dry matter tended to decrease as salinity increased, but less so when both NH4＋ and NO3- were present. Shoot biomass accumulated to significantly greater quantities under the mixed-N treatments than when produced using either NH4＋ or NO3- N-form alone. Although not statistically significant, the root biomasses showed a similar tendency. Generally, leaf proline and soluble shoot carbohydrate contents increased with increasing salinity in contrast to soluble protein which decreased regardless of the N source. Under salinity conditions, the concentration of Na＋ in shoot and root tissues was highest in ammonium-N treatment, while that of K＋ was highest in the mixed-N treatment.

Genetic,Developmental and Temporal Variability in Nitrate Accumulation and Nitrate Reductase Activity in Medicinal Herb Andrographis paniculata

There is a growing concern over the presence of high concentrations of nitrate in orally consumed herbal remedies. Since nitrate accumulation in the plant body can vary with spatial location in plant and plant development and temporally with photoperiod, understanding the relations between these factors and nitrate contents in the consumed herbs are vital for the development of agrotechnical strategies for nitrate avoidance. Therefore, the distribution profiles of nitrate content and nitrate reductase （NR） activity were analyzed in 14 accessions of Andrographis paniculata （Burm.f.） Wall. ex Nees., a medicinal plant widely used as a component of many herbal teas and medicinal infusions. Significant variation in nitrate accumulation in the plant was observed between the accessions, and most contained nitrate levels beyond the safety limit recommended according to the European Commission＇s Scientific Committee on Food. Nitrate content increased with plant development and leaf age, and that in leaf segment was higher in the middle of the leaf than at its tip or base; the nitrate concentration in plant organ followed the order of petiole 〉 leaf 〉 stem, and it was lower at mid-day than in the early morning or evening. Gradients of NR activity were negatively correlated with nitrate content in all studied temporal and spatial profiles. Identification of the characteristic spatial and developmental profiles of nitrate accumulation and NR activity in A. paniculata can guide the development of harvest strategies, aiming at minimizing nitrate contents in the consumed herbal tissue.