Inorganic nitrogen assimilation in plants of Austrlian rainforest communities

In a study of the plant communities of two Australian rainforests, it was found that pioner species had high levels of nitrate reductase (EC 1.6.6.1) and were predominantly leaf nitrate assimilators. Under- and over-storey species had low levels of shoot and root nitrate reductase activity, and many of them showed little capacity for nitrate reduction even when nitrate ions were freely available. Although closed-forest species have lower levels of nitrate reductase than those of gaps and forest margins, their total nitrogen contents were similar, suggesting the former utilize nitrogen sources other than nitrate ions. Glutamine synthetase (EC 6.3.1.2) was present in the leaves of all species examined. In the leaves of pioneer species the chloroplastic isoform of glutamine synthetase predominted, while in most of the species typical of closed-forest the cytosolic isoform accounted for at least 40% of total leaf activity. Low levels of chloroplastic glutamine synthetase were correlated with a low capacity for leaf nitrate reduction, and both are characteristic of many species that regenerate and grow for some time in shade. Low levels of chloroplastic glutamine synthetase imply that, in some of these woody plants, photorespiratory ammonia is re-assimilated via cytosolic glutamine synthetase.     

Effect of decreased irradiance on N and C metabolism in leaves and roots of maize

The effects of decreased irradiance on fresh and dry weight, root respiration, levels of carbohydrates and N-compounds, and extractable activities of enzymes involved in C and N metabolism were evaluated in maize ( Zea mays L. cv. Plauto) seedlings during the 7 days following transfer from 450 to 200 μmol m⁻² s⁻¹ PAR. The fresh weight of roots and stems, the initiation of new leaves, root respiration rate, and the accumulation of dry matter, soluble sugars, starch, malate and amino acids in both leaves and roots were strongly reduced at low irradiance. In contrast, the level of nitrate was increased in leaves and only marginally affected in roots. Leaf phosphoenolpyruvate carboxylase (EC 4.1.1.31) activity started to decrease after 24–34 h, whereas ribulose-1,5-bisphosphate carboxylase (EC 4.1.1.39) activity and chlorophyll content were unaffected or only slightly reduced. In both leaves and roots, the adjustment of N metabolism to low irradiance occurred through a relatively rapid (30% after 10 h) and large (60% after 3 days) decrease of nitrate reductase (NR; EC 1.6.6.1) activity, followed by slower and smaller changes in the activity of nitrite reductase (EC 1.7.7.1), glutamine synthetase (EC 6.3.1.2) and NAD-dependent glutamate dehydrogenase (EC 1.4.1.2). We suggest that the preferential decrease of NR activity relative to other N-assimilating enzymes may be important for preventing the accumulation of toxic N-compounds like ammonia in both leaf and root tissues.     

缺氮和复氮对菘蓝幼苗生长及氮代谢的影响

对基质育苗后水培的菘蓝进行缺氮与复氮处理,分析其生长情况及氮代谢产物含量的变化,探讨缺氮和复氮对菘蓝幼苗生长及氮代谢的影响,以提高菘蓝产量和品质以及栽培过程中的氮素利用效率。结果显示:(1)正常供氮条件下,菘蓝幼苗的叶绿素含量、谷氨酰胺合成酶(GS)活性、硝态氮含量、靛玉红含量为最高,而其株高、主根直径、根的鲜重与干重、叶的鲜重与干重、根系活力均最小。(2)缺氮处理增加了菘蓝幼苗的主根直径和根干重,提高其根系活力和硝酸还原酶(NR)活性,促进游离氨基酸在叶中的积累;但降低了GS的活性,也降低了叶中硝态氮、可溶性蛋白、靛玉红及根中游离氨基酸的含量;缺氮对叶中靛蓝的含量无明显影响。(3)复氮处理增加了菘蓝幼苗的株高、主根长、根鲜重、叶鲜重、叶干重,提高了其根系活力,降低了NR和GS的活性;与对照相比,复氮降低了叶中硝态氮含量,提高了叶中可溶性蛋白、靛蓝及根中游离氨基酸的含量,但对叶中游离氨基酸和靛玉红含量影响较小。研究表明,缺氮后再复氮有利于菘蓝幼苗叶的生长,同时有利于增加其叶内靛蓝含量,从而提高其产量和品质。     

Partitioning of inorganic nitrogen assimilation between the roots and shoots of cerrado and forest trees of contrasting plant communities of South East Brasil

Summary Woody plants growing in cerrado and forest communities of south-east Brasil were found to have low levels of nitrate reductase activity in their leaves suggesting that nitrate ions are not an important nitrogen source in these communities. Only in the leaves of species growing in areas of disturbance, such as gaps and forest margins, were high levels of nitrate reductase present. When pot-grown plants were supplied with nitrate, leaves and roots of almost all species responded by inducing increased levels of nitrate reductase. Pioneer or colonizing species exhibited highest levels of nitrate reductase and high shoot: root nitrate reductase activities. Glutamine synthetase, glutamate synthase and glutamate dehydrogenase were present in leaves and roots of the species examined.¹⁵N-labelled nitrate and ammonium were used to compare the assimilatory characteristics of two species:Enterolobium contortisiliquum, with a high capacity to reduce nitrate, andCalophyllum brasiliense, of low capacity. The rate of nitrate assimilation in the former was five times that of the latter. Both species had similar rates of ammonium assimilation. Results for eight species of contrasting habitats showed that leaf nitrogen content increased in parallel with xylem sap nitrogen concentrations, suggesting that the ability of the root system to acquire, assimilate or export nitrate determines shoot nitrogen status. These results emphasise the importance of nitrogen transport and metabolism in roots as determinants of whole plant nitrogen status.     

Comparative studies of diurnal variations of nitrate reductase activity in wheat, oat and barley

Diurnal variations of in vitro and in vivo (intact tissue assay) nitrate reductase (EC 1.6.6.1) activity and stability were examined in leaves of wheat ( Triticum aestivum L. cv. Runar), oat ( Avcna saliva L. cv. Mustang) and barley ( Hordeum vulgure L. cv. Agneta and cv. Gunillu). Nitrate reductase activity was generally higher for wheat than for oat and barley. However, the diurnal variations of nitrate reductase activity and stability were principally the same for all species, e.g. the high activity during the photoperiod was associated with low stability. All species showed a rapid (30-60 min) increase in the in vitro and in vivo activity when the light was switched on. When light was switched off the in vitro activity decreased rapidly whereas decrease in in vivo activity was slower. These experiments support the hypothesis that an activation/ deactivation mechanism is involved in the regulation of diurnal variations in nitrate reductase activity. Red light enhanced nitrate reductase activity in etiolated wheat and barley leaves. In green leaves, however, the daily increase in nitrate reductase activity was not induced by a brief red light treatment. Indications of different regulation mechanisms for the diurnal variations of nitrate reductase activity among the cereals were not found.     

NaHSO3对桃树的生理效应及产量、品质的影响

于桃树果实膨大期喷施100ppm NaHSO3可获得增产、优质、早熟的效果。此与NaHSO3能增加叶绿素含量、提高光合速率、比叶重、促进希尔反应,抑制硝酸还原酶、过氧化氢酶活性,增加单果重等多重生理效应相关。     

The Effect of Soil Water Regimes on Leaf Water Potential, Growth and Development of Soybeans

The growth and development of soybeans (Glycine max L. cv. Amsoy) was studied at soil matric potentials of ?0.1 to ?1.0 bars. Chlorophyll, photosynthesis, and leaf nitrogen per plant was greatest at ?4 bars leaf water potential. Leaf area, number of internodes, plant height and dry weight of vegetative parts declined as leaf water potential decreased from ?2 to ?19 bars. Nitrogen content and nitrate reductase activity per g fresh weight determined the percentage protein of individual seeds but nitrogen content and nitrate reductase activity per plant determined the amount of total seed protein. The protein synthesized in the seed changed little in amino acid composition with changes in leaf water potential. Leaf water potentials above or below ?4 bars decreased yield, total protein and total lipid but plants produced the largest percentage of individual seed protein at ?19 bars leaf water potential.     

Reversible Inactivation of Nitrate Reductase by NADH and the Occurrence of Partially Inactive Enzyme in the Wheat Leaf

Nitrate reductase from wheat (Triticum aestivum L. cv Bindawarra) leaves is inactivated by pretreatment with NADH, in the absence of nitrate, a 50% loss of activity occurring in 30 minutes at 25°C with 10 micromolar NADH. Nitrate (50 micromolar) prevented inactivation by 10 micromolar NADH while cyanide (1 micromolar) markedly enhanced the degree of inactivation.

A rapid reactivation of NADH-inactivated nitrate reductase occurred after treatment with 0.3 millimolar ferricyanide or exposure to light (230 milliwatts per square centimeter) plus 20 micromolar flavin adenine dinucleotide. When excess NADH was removed, the enzyme was also reactivated by autoxidation. Nitrate did not influence the rate of reactivation.

Leaf nitrate reductase, from plants grown for 12 days on 1 millimolar nitrate, isolated in the late photoperiod or dark period, was activated by ferricyanide or light treatment. This suggests that, at these times of the day, the nitrate reductase in the leaves of the low nitrate plants is in a partially inactive state (NADH-inactivated). The nitrate reductase from moisture-stressed plants showed a greater degree of activation after light treatment, and inactive enzyme in them was detected earlier in the photoperiod.

     

Influence of ammonium and nitrate nutrition on enzymatic activity in soybean and sunflower

Under conditions of controlled pH, nitrate and ammonium are equally effective in supporting the growth of young soybean (Glycine max var. Bansei) and sunflower (Helianthus annuus L. var., Mammoth Russian) plans. Soybean contains an active nitrate reductase in roots and leaves, but the low specific activity of this enzyme in sunflower leaves indicates a dependency upon the roots for nitrate reduction. Suppression of nitrate reductase activity in sunflower leaves may be due to high concentrations of ammonia received from the roots. Nitrate reductase activity in leaves of nitrate-supplied soybean and sunflower follows closely the distribution of nitrate reductase. For the roots of both species, glutamic acid dehydrogenase activity was greater with ammonium than with nitrate. The glutamic acid dehydrogenase of ammonium roots is wholly NADH-dependent, whereas that of nitrate roots is active with NADH and NADPH. In leaves, an NADPH-dependent glutamic acid dehydrogenase appears to be responsible for the assimilation of translocated ammonia and ammonia formed by nitrate reduction.     

Absence of nitrate reductase activity in San 9789 bleached leaves of barley seedlings (Hordeum vulgare cv. Midas)

Abstract San 9789 (norflurazone) blocks carotenoid synthesis which allows chlorophyll bleaching in the light, and has been used recently as a tool to study phytochrome responses without interference from photosynthetic pigments. By using this herbicide, we have found that nitrate reductase activity and light dependent nitrite reduction were lost simultaneously from achlorophyllous areas of barley leaves, with the green areas of the leaf tip still showing high activities. By contrast nitrate reductase is still present in the roots of herbicide treated plants. We suggest that intact chloroplasts are required for the presence of nitrate reductase in barley leaves.     

Repression of nitrate reductase in cucumber leaves caused by calcium deficiency

Growth of young cucumber plants was strongly inhibited, whencalcium was removed from the culture solution. The activitiesof nitrate reductase, glutamate dehydrogenase and glutaminesynthetase were investigated after the removal of calcium. Thoughthe activities of glutamine synthetase and glutamate dehydrogenasewere not altered much, nitrate reductase activity, measuredby in vitro and in vivo assays, decreased dramatically. Theloss of nitrate reductase activity coincided with the levelof nitrate in the leaves. When nitrate was supplied to the cucumberswith a nitrate deficiency, the plants induced nitrate reductasetogether with a distinct accumulation of nitrate. However, cucumberstreated for both calcium and nitrate deficiency failed to inducenitrate reductase and to accumulate nitrate on the additionof large amounts of nitrate. Leaf sections that had been treatedfor both calcium and nitrate deficiency could induce nitratereductase when floated on nitrate solution under the light.This indicates that the drastic loss of nitrate reductase causedby the removal of calcium was due mainly to the deficiency ofnitrate as the inducer in leaves. (Received December 19, 1979; )     

The occurrence of nitrate reductase in apple leaves

Nitrate reductase utilizing NADH or reduced flavin mononucleotide (FMNH₂) as electron donor was extracted from the leaves, stems and petioles, and roots of apple seedlings. Successful extraction was made possible by the use of insoluble polyvinylpyrrolidone (Polyclar AT) which forms insoluble complexes with polyphenols and tannins. The level of nitrate reductase per gram fresh weight was highest in the leaf tissue although the nitrate content of the roots was much higher than that of the leaves. Nitrite reductase activity was detected only in leaf extracts and was 4 times higher than nitrate reductase activity. Nitrate was found in all parts of young apple trees and trace amounts were also detected in mature leaves from mature trees. Nitrate reductase was induced in young leaves of apple seedlings and in mature leaves from 3 fruit-bearing varieties. An inhibitor of polyphenoloxidase, 2-mercaptobenzothiazole was used in both the inducing medium and the extracting medium in concentrations from 10⁻³ to 10⁻⁵m with no effect upon nitrate reductase activity.     

两种相思叶片光合作用对干旱的反应

比较了绢毛相思和大叶相思的叶特性,旱季的田间光合速率和供水短缺对光合速率、气孔传导率和蒸腾速率的影响。绢毛相思的比叶重、单位叶面积的叶绿素含量和叶绿素a/b均较大叶相思高,但叶片含水量略低。绢毛相思的中午时叶片水势为-0.6±0.05MPa,而大叶相思则为-1.18±0.07MPa。绢毛相思叶片水势降低时,叶片鲜重的变化较大叶相思大。旱季10月,两种相思的日平均光合速率相近似,但绢毛相思有较高的气孔传导率和蒸腾速率。干旱处理引起大叶相思叶片水势降低较绢毛相思大。当绢毛相思叶片水势从-0.76MPa降至-1.35MPa,日平均光合速率降低49.4％;而大叶相思,叶片水势从-1.22MPa降低至-2.2MPa,日平均光合速率降低55.0%。大叶相思叶片水势降低的幅度比较大,光合速率降低亦大。     

A comparison of the influence of iron on the growth and nitrate metabolism of Anabaena and Scenedesmus

A comparative study of growth and nitrate metabolism of Anabaena flos-aquae (Lyng.) Bréb. and Scenedesmus bijugatus var. seriatus Chodat investigated possible mechanisms for the iron-stimulated increases in growth specific for blue-green algae in mixed algal communities. Algae were separately grown in an morganic medium with varying concentrations of iron and nitrate to determine the effects on each organism. Iron was found to be a limiting nutrient for cultures of both Anabaena and Scenedesmus as determined by chlorophyll a concentrations and cell enumeration. Both iron and nitrate stimulated the specific activity of nitrate reductase, nitrite reductase, and glutamine synthetase in Anabaena. Iron enrichment did not increase the activity of the enzymes in Scenedesmus, but inhibited the activity of nitrate reductase and glutamine synthetase. The stimulation of growth by iron in cells grown under iron limiting conditions was associated with increased nitrate metabolism in Anabaena but not in Scenedesmus.     

Effects of nitrogen dioxide and nitrate nutrition on growth and nitrate assimilation in bean leaves

The influence of nutrient nitrate level (0-20 millimolar) on the effects of NO₂ (0-0.5 parts per million) on growth, K, photosynthetic pigment, N contents, and the activities of enzymes of N assimilation was studied in bean (Phaseolus vulgaris L. cv Kinghorn Wax) leaves. Exposing 7-day old bean seedlings for 5 days continuously to 0.02 to 0.5 parts per million NO₂ increased plant height, fresh weight, chlorophyll, carotenoid, organic N and nitrate contents, and nitrate reductase and glutamate synthase activities in the leaves of seedlings supplied with no external N. At 20 millimolar nitrate, most of the parameters examined were inhibited except for organic N and nitrate contents and glutamate synthase activity which increased in most cases. Generally, with an increase in NO₂ concentration, the stimulatory effect declined and/or the inhibitory effect increased. A 3-hour exposure of 12-day-old bean seedlings to 0.1 to 2.0 parts per million NO₂ increased nitrate content and nitrate reductase activity at each nutrient nitrate level except for a slight inhibition of enzyme activity during exposure to 2.0 parts per million NO₂ at 20 millimolar nitrate. The experiments demonstrated that the effect of NO₂ is strongly influenced by nutrient N level and that NO₂ is assimilated into organic nitrogenous compounds to serve as a source of N, only to a limited extent.     

Triadimenol Increases Nitrate Levels and Nitrate Reductase Activity in Canola Leaves

Nitrate reductase activity in the first true leaves of canola(Brassica napus L.) seedlings grown in one-quarter strengthHoagland's solution from seeds pretreated with triadimenol (0.3or 30 g (a.i.) kg^–1 of seed) was higher than controlsduring the growth period of 15 to 25 d after planting. Triadimenolalso increased chlorophyll levels, the increase being more pronouncedat its lower concentration. The treatment also increased theweight and nitrate content of the leaves. When seedlings weregrown in nutrient solution containing 1 to 20 mM nitrate, theincrease in nitrate reductase activity by triadimenol was higherat lower rather than at higher nitrate concentrations. The nitratelevels and Kjeldahl nitrogen in the triadimenol-treated leaveswas higher than the controls at concentrations of added nitrateabove 2 mM. Addition of nitrate to plants grown in ammonium,increased nitrate reductase activity more in plants grown fromtriadimenol-treated seeds than controls. However, addition of10µM triadimenol for 24 h to ammonium-grown plants hadlittle effect on enzyme activity, both in the absence as wellas the presence of nitrate. This study demonstrates that triadimenolincreases nitrate reductase activity and nitrate accumulationin the leaves and at least part of the increased enzyme activityis independent of nitrate accumulation. Key words: Triazoles, nitrate content, nitrate reductase activity     

Effect of light and glucose on the induction of nitrate reductase and on the distribution of nitrate in etiolated barley leaves

Barley seedlings grown in the dark with 10 mm KNO(3) have low levels of nitrate reductase activity even though large amounts of No(3) (-) accumulate in the leaves. When the leaves are excised and transferred to the light, there is an increase in nitrate reductase activity both in the presence and absence of exogenous NO(3) (-). When the leaves are transferred to a glucose solution (0.05 m) but kept in the dark, induction of nitrate reductase activity occurs only when fresh NO(3) (-) is added to the system.In dark-grown leaves, there are small traces of NO(3) (-) in a "metabolic pool." Addition of glucose does not alter this distribution. Light, on the other hand, results in an appreciable accumulation of NO(3) (-) in the metabolic pool. There is a linear correlation between nitrate reductase activity and the size of the metabolic NO(3) (-) pool. Our results thus suggest that NO(3) (-) accumulates in a storage pool when seedlings are grown in continuous darkness. The transfer of this NO(3) (-) to an active metabolic pool is mediated by light but not by glucose. We believe that this transfer of NO(3) (-) leads to the induction of nitrate reductase. When NO(3) (-) is included in the medium, both light and glucose increase its incorporation into the metabolic pool. The results suggest two mechanisms for regulating the metabolic NO(3) (-) pool: (a) a transfer from the storage pool which requires light; and (b) a transfer from the external medium which requires either glucose or light.     

The Occurrence of Nitrate Reduction in the Leaves of Woody Plants

Nitrate reductase activities greater than 02 µmol h^–1g^–1 f. wt, measured by an in vivo assay, occurred in 41per cent of a large sample (555 species) of woody plants. Ifseveral taxonomic groups (Gymnosperms, Ericaceae and Proteaceae)with consistently low activities were discounted activitiesgreater than 02 µmol h^–1 g^–1 f. wt occurredin 73 per cent of the species. This compares with 93 per centin herbaceous species, suggesting that leaf nitrate reductionis of common occurrence in woody plants. In a small sample ofspecies leaf nitrate reductase activity correlated with nitrateconcentration in the xylem sap. Low activities occurred consistentlyin the Gymnosperms, Ericaceae and Proteaceae. Feeding cut shootsof representatives of these groups with nitrate caused inductionof leaf nitrate reductase activity in the Gymnosperms and Proteaceae,but only limited induction in the Ericaceae. The Ericaceae,with the exception of two species, had low activities and lownitrate reductase inducibility. Root assimilation may predominatein the Gymnosperms and Proteaceae. It is suggested that nitratereduction generally occurs in the leaves of trees from a varietyof plant communities and that this may be related to the lowerenergy cost of leaf, as opposed to root, nitrate assimilation. Nitrate reductase, trees and shrubs, leaves, nitrate assimilation, nitrate translocation, nitrate reductase induction, energy cost, plant ecology     

浙江天台山七子花等6种阔叶树光合生态特性

 对分布在浙江天台山的七子花(Heptacodium miconioides)等6种主要阔叶树的光合生理生态特性进行了研究,结果表明：1)夏季6种植物光合日进程均为“双峰”型,有明显的光合“午休”现象。日均净光合速率月变化呈“单峰”型,8月是一年的高峰期。日均和5～11月平均净光合速率最高的是东南石栎(Lithocarpus harlandii),最低的是天台阔叶槭(Acer amplum var. tientaiense）,七子花处于中下水平。2)相对常绿树种而言,七子花的光补偿点较高,光饱和点较低,对光