Distribution of Nitrogen during Growth of Sunflower (Helianthus annuus L.)

The accumulation, distribution and redistribution of dry matterand nitrogen is described for Helianthus annuus L. cv. Hysun21 grown on 6 mM urea in glasshouse culture. Seed dry matterand nitrogen were transferred to seedlings with net efficienciesof 40 and 86 per cent respectively. At flowering, the stem hadmost of the plant's dry matter and the leaves most of its nitrogen.About 35 per cent of the plant's nitrogen accumulated afterthree-row anthesis. The amount of protein in vegetative parts,especially leaves, declined after flowering. Concentrationsof free amino compounds also decreased during growth. Matureseeds had 38 per cent of the total plant dry weight and 68 percent of the total nitrogen. Seeds acquired 33 per cent of theirdry matter and nitrogen from redistribution from above-groundplant parts. The stem was most important for storage of carbohydrate,leaves the most important for nitrogen. Over 50 per cent ofthe nitrogen in the stem and leaves was redistributed. Plantsthat received 6 mM nitrate accumulated more dry matter thanurea-grown plants. Seeds from nitrate-grown plants were heavier(58 mg) than those of urea-grown plants (46 mg), and their percentageoil was greater (50 and 41 respectively). The amount of nitrogenper seed was the same. Little or no urea was detected in xylem sap of plants suppliedwith 5 mM urea, but it was detected in sap of plants which received25 mM. Concentrations of urea and amino compounds in the sapdecreased up the stem. Plants supplied with nitrate had mostof the nitrogen in xylem sap as NO₂^–, suggesting littlenitrate reduction in roots. Plants grown on 6 mM nitrate andchanged to high levels of urea-nitrogen for 14 days still hadhigh levels of nitrate; little nitrate remained in plants receivinglow levels of urea. When urea is applied in irrigation waterto field-grown sunflower, the nitrogen is subsequently takenup as nitrate due to rapid nitrogen transformations in the soil. Helianthus annuus L., sunflower, urea, nitrate, nitrogen transport, xylem sap, nitrogen accumulation nitrogen distribution     

Rhizobium strain effects on yield and bleeding sap amino compounds in Pisum sativum

Bleeding sap composition, dry matter production and nitrogen distribution in pea ( Pisum sativum L. cv. 'Bodil') grown with and without nitrate and nodulated with either Rhizobium leguminosarum strain 128c53 or strain 1044 were compared. Nitrate increased the total dry matter production of both symbioses, but decreased both the proportions of below-ground dry matter to total dry matter production and nodule dry matter to total below-ground dry matter production. The total dry matter yield and N-accumulation was greater in the symbiosis with strain 1044, whereas the accumulation of N in the roots plus nodules relative to the total N-accumulation was greater with strain 128c53 due to a higher production of nodule tissue. The root bleeding sap of the symbiosis with the greater yield (strain 1044) contained high levels of asparagine and aspartic acid. In the 128c53 symbiosis, glutamine plus bomoserine accounted for a higher percentage of the organic solutes transporting newly assimilated nitrogen from the root system than in the association with 1044. The Rhizobium strain effect on amino compound composition of the bleeding sap may indicate an influence of the bacteroids on either the N-assimilatory enzyme system in the plant cytosol, or on the pools of the Krebs cycle intermediates or related compounds in the nodules.     

The Distribution of Nitrate Assimilation Between Root and Shoot in Vicia faba L.

Nitrate assimilation was examined in two cultivars (Banner Winterand Herz Freya) of Vicia faba L. supplied with a range of nitrateconcentrations. The distribution between root and shoot wasassessed. The cultivars showed responses to increased applied nitrateconcentration. Total plant dry weight and carbon content remainedconstant while shoot: root dry weight ratio, total plant nitrogen,total plant leaf area and specific leaf area (SLA) all increased.The proportion of total plant nitrate and nitrate reductase(NR) activity found in the shoot of both cultivars increasedwith applied nitrate concentrations as did NO₃^–: Kjeldahl-Nratios of xylem sap. The cultivars differed in that a greaterproportion of total plant NR activity occurred in the shootof cv. Herz Freya at all applied nitrate concentrations, andits xylem sap NO₃^–: Kjeldahl-N ratio and SLA were consistentlygreater. It is concluded that the distribution of nitrate assimilationbetween root and shoot of V. faba varies both with cultivarand with external nitrate concentration. Vicia faba L., field bean, nitrate assimilation, nitrate reductase, xylem sap analysis     

Ureide assay for measuring nitrogen fixation by nodulated soybean calibrated by N methods

We report experiments to quantify the relationships between the relative abundance of ureide-N in root-bleeding sap, vacuum-extracted sap, and hot water extracts of stems and petioles of nodulated soybean (Glycine max [L.] Merrill cv Bragg) and the proportion of plant N derived from nitrogen fixation. Additional experiments examined the effects of plant genotype and strain of rhizobia on these relationships. In each of the five experiments reported, plants of cv Bragg (experiment 1), cv Lincoln (experiments 3, 4, 5), or six cultivars/genotypes (experiment 2) were grown in a sand:vermiculite mixture in large pots in a naturally lit, temperature-controlled glasshouse during summer. Pots were inoculated at sowing with effective Bradyrhizobium japonicum CB1809 (USDA 136) or with one of 21 different strains of rhizobia. The proportions of plant N derived from nitrogen fixation were determined using ¹⁵N dilution. In one experiment with CB1809, plants were supplied throughout growth with either N-free nutrients or with nutrients supplemented with 1, 2, 4, or 8 millimolar ¹⁵N-nitrate and harvested on eight occasions between V6 and R7 for root-bleeding sap, vacuum-extracted sap, stems (including petioles), and whole plant dry matter. Analyses of the saps and stem extracts for ureides (allantoin plus allantoic acid), α-amino-N, and nitrate, and of dry matter for N and ¹⁵N, indicated a positive effect of nitrate supply on concentrations of nitrate in saps and extracts and a negative effect on ureides and on the proportion of plant N derived from nitrogen fixation. The relative abundance of ureide-N in root-bleeding sap, vacuum-extracted sap (100 [ureide-N]/[ureide-N+ α-amino-N + nitrate-N]) and stem extracts (100 [ureide-N]/[ureide-N + nitrate-N]) and the proportion of plant N, derived from nitrogen fixation between successive samplings were highly correlated (r = 0.97-1.00). For each variable, two standard curves were prepared to account for the shifts in the compositions of N solutes of xylem saps and extracts after flowering which were not related to a change in nitrogen fixation. Relationships between relative ureide-N and the proportion of plant N derived from nitrogen fixation were not affected by plant genotype or by strain of rhizobia. Therefore, assessment of nitrogen fixation by soybean using the ureide technique should now be possible with the standard curves presented, irrespective of genotype or strain of rhizobia occupying the nodules.     

强筋与弱筋小麦籽粒蛋白质组分与加工品质对灌浆期弱光的响应

选用强筋小麦品种济麦20和弱筋小麦品种山农1391,在大田试验条件下,分别于籽粒灌浆前期(花后6—9 d)、中期(花后16—19 d)和后期(花后26—29 d)对小麦进行弱光照处理,研究了籽粒产量、蛋白质组分及加工品质的变化。灌浆期弱光显著降低小麦籽粒产量,灌浆中期对济麦20和灌浆后期对山农1391的产量降幅最大。弱光处理后,籽粒氮素积累量及氮素收获指数减少。但弱光使籽粒蛋白质含量显著升高,其中灌浆中期弱光升幅最大,原因可能是由于其粒重降低造成的。弱光对可溶性谷蛋白无显著影响,但增加不溶性谷蛋白含量,使谷蛋白聚合指数显著升高,面团形成时间和稳定时间亦升高,籽粒灌浆中、后期弱光对上述指标的影响较前期大。灌浆期短暂的弱光照对改善强筋小麦粉质仪参数有利,但使弱筋小麦变劣;并均伴随籽粒产量的显著降低这一不利影响。     

Growth, water use efficiency, and proline content of hydroponically grown tomato plants as affected by nitrogen source and nutrient concentration

Tomato plants (Lycopersicon esculentum Mill. cv. Counter) were grown in 12-L polyethylene containers in aerated and CaCO₃-buffered nutrient solutions containing different concentrations of complete stock solutions with either nitrate (stock solution N) or ammonium (stock solution A) as the only nitrogen source (X1 = standard concentration with 5 mM NO₃ ^–-N or NH₄ ⁺-N, and X3, X5.5, X8 and X11 = 3, 5.5, 8, 11 times the standard concentration), or a mixture of both stock solutions (N:A ratio = 100:0, 75:25, 50:50, 25:75, 0:100) at moderate nutrient concentration (X3). Total dry matter production and fruit dry weight were only slightly affected by increasing nutrient concentration if nitrate was supplied as the sole nitrogen source. Compared to nitrate, ammonium nitrogen caused a decrease in total dry weight (32–86% between X1 and X11), but led to an increase in both total dry weight and fruit dry weight (11% and 30%) at low concentration if supplied in addition to nitrate nitrogen (N:A ratio = 75:25). Dry matter partitioning in plants was affected by the strength of the nutrient solution, but even more by ammonium nitrogen. Fruits accumulated relatively less dry matter than did the vegetative parts of tomato plants when supplied with nutrient solutions containing ammonium as the only nitrogen source (fruit dry weight to total dry weight ratio 0.37 and 0.15 at low and high nutrient concentration), while nitrate nitrogen rather supported an increase in dry matter accumulation in the reproductive organs (fruit dry weight to total dry weight ratio 0.39–0.46). The water use efficiency (WUE) was only slightly affected by the strength of the nutrient solutions containing nitrate nitrogen (2.9–3.4 g DW (kg H₂O)^–1), while ammonium nitrogen led to a decrease in WUE from 2.4 to 1.3 g DW (kg H₂O)^–1at low (X1) and high (X11) nutrient concentration, respectively. The proline content of leaves fluctuated (0.1–5.0 mol (g fresh weight)^–1) according to nutrient concentration and global radiation, and reflected enhanced sensitivity of plants to these potential stress factors if ammonium was the predominant N source supplied. It was concluded, that proline is a reliable indicator of the environmental stress imposed on hydroponically grown tomato plants.     

Dry matter response of ryegrass to ammonium and nitrate sources of nitrogen as a function of soil texture and moisture

Summary InLolium perenne cv. S23 grown in pots of soil to which nitrogen was applied at rates of 0, 60, 120 and 180 mg N/kg, ammonium significantly increased root mass compared with nitrate, whereas both nitrogen sources produced similar yields of herbage. Total dry matter production in the herbage and roots increased within the textural sequence: loamy sand, coarse sandy loam and loam. The increases in the latter two soils over the loamy sand were 35% and 50%, respectively. Depletions of available water of 50% and 80% reduced yields at the first harvest by 19% and 50% compared with the field capacity. The corresponding reductions in the second harvest were only 16% and 10%, because residual effects were then limiting. The amount of dry matter produced per unit of nitrogen absorbed indicated that textural class was less restrictive than moisture supply to efficient use of nitrogen within the plant. Furthermore, its efficient physiological use was limited at the 50% depletion, although its absorption from the soil was not affected. The results illustrated the inefficiency of the substitution of nitrogen for soil moisture: even at low yield levels three times more nitrogen was absorbed per unit increase in dry matter at 80% depletion of available water compared with the field capacity. The significant first-order interactions that affected yield were moisture by soils, and moisture by nitrogen rate.     

The effects of light and nitrogen on photosynthesis,leaf characteristics,and dry matter allocation in the chaparral shrub,Diplacus aurantiacus

Summary Plants of Diplacus aurantiacus, a successional shrub common in California chaparral, were grown under controlled conditions in which either quantum flux density or nitrogen availability was varied. Photosynthesis and leaf nitrogen content were determined on a leaf area and a leaf weight basis, and whole plant growth was monitored.There was a direct relationship between photosynthesis and leaf nitrogen content on both area and weight bases. Reduced light intensity of the growth environment resulted in reductions in light-saturated photosynthesis and nitrogen content on an area basis, but not on a weight basis. With reduced nitrogen availability, photosynthesis and leaf nitrogen content per unit leaf weight decreased.Resource use efficiency increased as the resource became more limiting. The results are consistent with a model of plant growth in which net carbon gain of the leaf is maximized. Abbreviations. For brevity, the following set of abbreviations is used in presenting and discussing the results. P/area and N/area are, respectively, photosynthesis and leaf nitrogen content per unit leaf area. P/wt and N/wt are the same quantities per unit leaf dry weight. SLW (specific leaf weight) is dry weight per unit leaf area. RGR (relative growth rate) is the relative rate of increase in shoot dry matter per day     

The relation between cell size, ploidy level and nitrate concentration in lettuce

In two experiments the relation between cell size, ploidy level and nitrate concentration of genotypes of lettuce ( Lactuca saliva L.) was investigated. Artificial increase of cell size by application of gibberellic acid to young plants decreased the percentage dry weight and the concentration of organic acids in the plant sap and increased the nitrate concentration of the shoot. Application of chlormequat chloride caused the opposite effects. Tetraploid genotypes of lettuce had larger cells, a lower nitrate concentration and a higher concentration of organic solutes than diploid genotypes. Genotypical differences in nitrate concentration could not be explained by differences in cell size, but were consistently related to differences in concentration of organic acids in plant sap. The percentage dry weight of genotypes was positively correlated with the concentration of organic acids in plant sap. However, differences in nitrate concentration were also found among genotypes with comparable dry matter content. These differences could be caused by differences in partitioning of photosynthates over structural components and organic acids in the vacuoles. Mono-saccharides seem to be less important than organic acids for explaining genotypical differences in nitrate level, because the concentration of monosaccharides was much lower than that of organic acids and because a negative relation between the concentration of monosaccharides and of nitrate was not found in every case. Genotypical differences in nitrate accumulation were not related to differences in osmolarity.     

不同水氮水平下小麦品种对光、水和氮利用效率的权衡

通过再裂区设计田间试验,以3个春小麦品种(和尚头、西旱2号和宁春4号)为材料,设置两个灌溉水平(充分灌水4500 m³·hm^-2和有限灌水3000 m³·hm^-2)和5个施氮水平(0、75、150、225、300 kg N·hm^-2),研究小麦光能利用效率(LUE)、水分利用效率(WUE)、氮素利用效率(NUE)对水氮的响应特性及其相互关系.结果表明: 3个小麦品种间LUE、WUE和NUE差异显著.在一定范围内增加灌水和施氮量则LUE升高,过量施氮则LUE下降.强抗旱和中等抗旱品种(和尚头和西旱2号)WUE受灌水量的影响比不抗旱品种(宁春4号)小.施氮可以调节小麦WUE,中等施氮水平(和尚头和西旱2号在150 kg N·hm^-2时,宁春4号在225 kg N·hm^-2时)有最高的WUE.随施氮量增加,植株氮素累积量先增后减,氮素干物质生产效率(NUE_b)、氮素收获指数(NHI)、氮肥农学利用效率(NAE)和氮肥偏生产力(PFP)均显著降低.灌溉水平对NHI无显著影响;随灌水量增加,小麦氮素积累量显著增加,强抗旱和中等抗旱品种NUE_b和NAE显著降低,不抗旱品种 NUE_b和PFP显著升高,对其他指标无显著影响.3个小麦品种氮素获取能力与氮素利用效率呈极显著负相关,NUE_b与LUE、WUE呈显著负相关,LUE与WUE呈显著正相关,春小麦氮素利用效率与光能利用效率、水分利用效率间存在明显的权衡关系.当灌水量为3000 m³·hm^-2,强抗旱和中等抗旱品种在150 kg N·hm^-2,不抗旱品种在225 kg N·hm^-2时,有较高的资源利用效率.     

Nitrate Accumulation and Osmotic Regulation in Italian Ryegrass (Lolium multiflorum Lam.)

The role of nitrate accumulation was studied in osmotic adaptationof Italian ryegrass (Lolium multiflorum Lam. cv. Romo). Plantswere grown under different light intensities (68 and 143 W m^–2)and on Hoagland nutrient solution with a solute potential of0.035 MPa and –0.335 MPa. The solute potential of thenutrient solution was decreased by addition of NaCl, which wastaken up by the plant, and PEG 6000 which was not. At each growingcondition the solute potential of the expressed plant sap wasconstant during the experimental period of 19 d, but was decreasedby increase in light intensity and addition of osmotic substancesin the root medium. At sugar concentrations between 20 and 60mg per gram plant water a change in sugar concentration is osmoticallyfully compensated for by an opposite change in nitrate concentration.At sugar concentrations lower than 20 mg per gram plant waterthere is an overcompensation of nitrate. The overcompensationincrease is attributed to a concomitant decrease of other organicsolutes such as amino acids and organic acids. When NaG is addedto the nutrient solution, the nitrate concentration in the plantdecreases and the solute potential is decreased by uptake ofchloride. With PEG the nitrate content of the plant also decreased.The solute potential of the plant sap is decreased by accumulationof sugar, at least at the high light intensity. Key words: Lolium multiflorum, Nitrate accumulation, Light intensity, Osmotic regulation     

光强对烟草幼苗形态和生理指标的影响

通过白纱布遮荫模拟不同光生境条件(透光率分别为100%、68.2%、35.4%和16.7%),研究了光强因子对烟草幼苗形态和生理指标的影响.结果表明:随相对光强的减弱,幼苗高度增加,茎粗、干鲜比、叶片厚度和单位叶面积质量均呈降低趋势,幼苗干物质积累减少,但其对叶数的影响不大.弱光条件下,叶片自由水、叶绿素、总氮和蛋白质含量增加,束缚水含量降低,叶绿素a/b值减小,转化酶活性降低;烟草幼苗根系相对不发达,根冠比和根生物量减小,根系活力降低.表明弱光条件不利于培育烟草壮苗,生产中应尽可能改善苗床的光照条件.     

Effects of Nitrogen Fertilizer on Growth and Yield of Spring Wheat

Nine amounts of nitrogen fertilizer, ranging from 0 to 200 kgN ha^–1, were applied to spring wheat cv. Kleiber in the3 years 1972-1974. In 1972 grain dry weight with 125 kg N ha^–1or more was 100 g m^–2 (23 per cent) greater than withoutnitrogen. Grain yield was unaffected by nitrogen in the otheryears. Leaf area at and after anthesis was increased throughoutthe range of nitrogen tested, most in 1972 and least in 1973.Consequently, the addition of 200 kg N ha^–1 decreasedthe amount of grain produced per unit of leaf area by approximately25 per cent in all years. The dry weight of leaves and stems at anthesis and maturitywas increased by nitrogen in all years, similarly to leaf area.However, the change in stem dry weight between anthesis andmaturity was not affected by nitrogen; stems increased in dryweight for about 20 days after anthesis and then decreased tovalues similar to those at anthesis. The uptake of CO₂ per unit area of flag leaf or second leaf(leaf below the flag leaf) was slightly decreased by nitrogenwhen the increase in leaf area caused by nitrogen appreciablydecreased the light intensity at the surface of these leaves.In spite of such decreases the CO₂ absorbed by flag and secondleaves per unit area of land was always increased by nitrogen,and relatively more than was grain yield. It is suggested that increases in respiratory loss of CO₂ withincreasing nitrogen fertilizer may explain why nitrogen increasedvegetative growth and leaf area relatively more than grain yield.     

Effects of Nitrogen on the Development and Growth of the Potato Plant. 2. The Partitioning of Dry Matter, Nitrogen and Nitrate

Potatoes (Solanum tuberosum L.) were planted in pots in a temperature-controlledglasshouse The treatments consisted of three levels of nitrogensupply, ie 25, 8 and 16 g N per pot (treatments called N1, N2and N3) The accumulation rates of dry matter and nitrogen showedan upper limit of response to nitrogen supply, N3 plants continuedto accumulate dry matter and N at a constant rate for a longerperiod of time than N2 and N1 plants The uptake of nitrogenslowed earlier in time than the rate of dry matter accumulationin all treatments. The proportion of the dry matter in tubersof mature plants was not affected by nitrogen treatment, butthe start of tuber bulking was delayed in the N3 plants Thefinal proportion of total plant nitrogen in the tubers was similarfor all treatments The concentration of nitrogen in the drymatter of mature plants increased with the level of N supplyMaximum haulm weight increased with the level of N supply Apicallateral branches of the first and second order made up largerproportions of the total haulm dry weight and total leaf areaas more nitrogen was supplied. Yet, the distribution of drymatter over stems and leaves was not different between nitrogentreatments Stems were the most responsive to N treatment interms of N concentrations In each of the component organs (stems, leaves, tubers) theconcentration of nitrogen declined with time Fairly strong associationswere observed between the concentrations of N in component organs.The concentration of nitrate in leaves usually increased initiallywith leaf age, peaked and declined. A substantial part of thedifferences between treatments in the concentrations of N inleaf dry matter were attributable to differences in nitrateconcentration Nitrate in stems and tubers fell virtually belowthe limit of detection at total nitrogen concentrations of lessthan 1%, but increased in proportion to total N above that threshold,especially in stems Potato, Solanum tuberosum L, dry matter production, dry matter distribution, nitrogen nutrition, nitrogen distribution, nitrogen concentration     

Competitive ability and tolerance of organically grown wheat cultivars to natural weed infestations

Competitive ability of a traditional winter wheat cultivar (Maris Widgeon) was compared with two modem cultivars (Hereward and Genesis) when grown organically in each of four seasons in Gloucestershire, UK. In two seasons, cultivars were compared at two sowing dates (September and October or November). Cv. Maris Widgeon was the tallest cultivar and intercepted most photosynthetically active radiation (PAR), particularly if sown early. Cv. Hereward was taller than cv. Genesis when sown early. Cv. Maris Widgeon accumulated most nitrogen and dry matter early in the season (until the end of March) when sown early, but not when sown late. Relative nitrogen and dry matter accumulation by cultivars later in the season depended on season and sowing date. In one season cv. Maris Widgeon had significantly more early season ground cover. Cultivars did not differ significantly in early tiller production. Although most of these indirect measures of competitive ability were greater for the older variety cv. Maris Widgeon, infestation of Veronica spp. was greater in plots of this cultivar than in plots of either one or both of the shorter cultivars in two successive seasons. In the 1993/94 season, the soil seedbank from plots previously cropped with cv. Maris Widgeon produced more seedlings of Sinapis awensis. In the 1994 / 95 season, cv. Maris Widgeon plots contained less weed in terms of ground cover, numbers, dry matter and nitrogen than the other cultivars, and soil sampled from plots previously cropped with cv. Hereward sown late gave rise to larger numbers of weeds than cv. Maris Widgeon. Sowing date affected weed burdens and emergence to a much greater extent than wheat cultivar. In years and sowing date treatments with relatively low weed presence the shorter cultivars tended to yield more than cv. Maris Widgeon. When weed burdens were severe cv. Maris Widgeon yields were equal to or greater than those of either cvs Hereward or Genesis. The results suggest that the traditional tall cv. Maris Widgeon could be used beneficially to tolerate weeds in organic systems when high weed infestations were anticipated, but could not be relied upon to suppress weed development, and in some circumstances could actually encourage certain species.     

Translocation of nitrogen in osmotically stressed wheat seedlings

Wheat (Triticum aestivum L., cv. Drabant) seedlings were grown in a ‘split root’ system where either the whole root system or one root half was subjected to osmotic stress for 24 h, using 200 g polyethylene glycol (PEG, molecular weight 4000) dm^?3 nutrient solution. ¹⁵N-Labelled nitrate was fed to one of the root compartments and total N and ¹⁵N-labelling were measured in plant material and xylem sap. Untreated plants translocated 87% of the N taken up to the shoot, and 10% of this was then retranslocated back to the root. Recalculated on a root nitrogen basis, 36% of the label recovered in the root after 24 h had passed through the shoot. Significant labelling of xylem sap collected from non-labelled roots indicated cycling of organic N through the roots. PEG-treatment of the whole root system caused significant water loss in both roots and shoots. Uptake of nitrate and retranslocation of N to roots were inhibited, whereas cycling of organic nitrogen through the root was still measurable. Treatment of half the root system with PEG had minor effects on shoot water content, but reduced the water content of the treated root part. The total uptake of nitrate by the root system was unaffected, and the effect on the treated root half was comparatively small. Nitrate reductase activity (NRA) declined in PEG-treated roots even if high nitrate uptake rates were maintained. Shoot NRA was unaffected by osmotic stress. The data indicate that the reduction in water content of the root per se has only small effects on nitrate uptake. Major inhibition of nitrate uptake was observed only after treatment of a sufficiently large portion of the root system to given an effect on shoot water content.     

Nitrogen metabolism and senescence-associated changes during growth of carnation flowers

Nitrogen metabolism including nitrate reductase (EC 1.6.6.1), glutamate dehydroge-nase (EC 1.4.1.2) and glutamate-oxalacetate aminotransferase (EC 2.6.1.1) activities were studied during growth of petals taken from carnation flowers ( Dianthus caryophyllus L. cv. Sir Arthur) together with senescence parameters (lipid hydroper-oxides, soluble amino acids and permeability). A slight decline in nitrogen percentage on a dry weight basis was found together with a sharp decrease in nitrate reduct-ase, glutamate-oxalacetate aminotransferase and glutamate dehydrogenase activities during the maximum growth phase, which was characterized by increase in respiration, dry weight, length, organic nitrogen and DNA per petal. Changes generally associated with senescence, like lipid hydroperoxide and soluble ammo nitrogen accumulation and increases in permeability began to appear already during early growth. The results indicate that permeability and proteolysis may be closely related. The possible significance of the decrease in nitrogen percentage and enzyme activities during growth of petals is discussed.     

Transport of Recently Assimilated15N Nitrogen to Individual Spikelets in Spring Wheat Grown in Culture Solution

Two cultivars of spring wheat ( Triticum aestivum L.), Sport(high protein) and WL4 (low protein), were grown to maturityin culture solution. Nitrogen in the form of nitrate was addedin daily doses at stepwise-decreasing relative rates to ensurenormal development, and both cultivars received the same totalamount of N during development. At weekly intervals from anthesisto maturity the daily nitrate dose was, for selected groupsof plants, labelled with¹⁵N. After the labelling period theselected plants were harvested and analysed. The cultivar WL4produced more biomass than Sport, as well as more spikeletsand more grains per ear, with a higher mean grain weight, suchthat grain yield of WL4 was 57% greater than Sport. The earsof both cultivars were heterogenous: mean grain weight was highestin middle spikelets, which also contained more grains; the Ncontent followed the pattern of dry weight with more N in themiddle spikelets; but the N concentration was practically thesame in all spikelets (2.15% of d. wt in WL4 and 3.33% in Sport).The distribution of¹⁵N showed that the main stem ear maturedmuch earlier than tiller ears. The results of this nitrogen-labellingexperiment show that, late in development, substantial amountsof recently-absorbed N were immediately assimilated and transportedto the ears. Transport of¹⁵N decreased earlier to the top spikeletsthan to the bottom spikelets. As both cultivars were grown underidentical conditions and both received the same amount of Nit was concluded that the difference in grain N concentrationwas not caused by differences in the capacity of N assimilationand translocation but rather by different rates of accumulationof non-nitrogenous dry matter in the grains. Ear; grain; nitrate; nitrogen transport; Triticum aestivum L.; yield     

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.     

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。