Der Einfluß von P-Ernährung und pH auf die Phosphataseaktivität von Zuckerrübenwurzeln

The influence of phosphorus nutrition and pH on phosphatase activity of sugar beet roots For the determination of acid phosphatase activity (P_ase) of sugar beet roots (cultivar: Reka), plants were cultivated in nutrient solution with 1 or 100 μM P in a growth chamber for 12, 18, 24, 30, 36 and 42 days. The phosphatase activity of intact roots was measured in buffer solutions with pH 4 to 7.2 and 14 mM p-Nitrophenylphosphate (NPP) after 10 min of incubation at 20°C. The influence of P nutrition on P_ase activity was significant at all intervals. At P deficiency the activity was increased by a factor of 4 to 20. During the experimental period the pH optimum was 6. At pH 5 and 7.2 the P_ase activity reached only 63 and 64% respectively of the optimum value. At P deficiency (1 μmol P L^—1) the absolute rate of NPP-hydrolysis at pH 6 was 144 nmol min¹ m¹ root length (day 12 to 36). The plants which received optimum P supply showed only 10% of this value. Sugar beet roots with P deficiency have a high potential of P_ase activity from the acid to the neutral pH-range. Therefore, under this condition they may effectively use dissolved organic phosphorus compounds.     

Ermittlung kinetischer Parameter der sauren Phosphatasen intakter Zuckerrübenwurzeln bei variierter Phosphaternährung

Determination of kinetic parameters of acid phosphatases in intact sugar beet roots of variable phosphorus nutrition Organically bound phosphorus has to be hydrolysed before its P can be taken up by plants. Both microbes and plant roots possess phosphatases, which could be of importance especially in soils with low concentrations of inorganic phosphorus in the soil solution. This could be the reason why nutrient uptake models underestimate the P-uptake by plants when P-mobilization by the phosphatases of roots is not taken into consideration. Therefore the activity of acid phosphatases (P_ase) was determined to answer the following questions: 1) To which extent does the root bound acid phosphatase (P_ase) follow Michaelis-Menten kinetics? 2) By which of the four linear transformations of the Michaelis-Menten equation (Lineweaver/Burk, Hanes, Eadie/Hofstee, Eisenthal/Cornish-Bowden) can plausible values of V_max and K_m be determined? 3) Which effect has the P nutrition of the plant on these kinetic parameters? Sugar beet plants were grown in full nutrient solution containing 1 and 100 μM P respectively. The P_ase activity of the intact roots was measured at pH 5 using p-nitrophenylphosphate (25—15000 μM p-NPP). V_max values were calculated per m root length. Acid phosphatase activity principally followed Michaelis-Menten kinetics. Transformations and calculations of V_max and K_m after Eadie/Hofstee and Eisenthal/Cornish-Bowden suggested the existence of at least two enzyme systems (P_{ase 1}, P_{ase 2}). The following kinetic parameters were found: P_{ase 1}: P deficient plants: V_max: 43—45 nmol m^—1 min^—1, K_m: 31—37 μM NPP; P sufficient plants: V_max: 7 nmol m^—1 min^—1, K_m: 47—53 μM NPP. P_{ase 2}: P deficient plants: V_max: 230—293 nmol m^—1 min^—1, K_m: 1579—3845 μM NPP; P sufficient plants: V_max: 123—171 nmol m^—1 min^—1, K_m: 3027—7000 μM NPP. Thus plants with sufficient P nutrition have a lower affinity to P_org and a lower hydrolysis of P_org. For P nutrition of crops P_{ase 1} might be the most important enzyme.     

Entwicklung und Ertrag von Sommerweizen in Hydrokultur unter dem Einfluß verschiedener Ernährungsbedingungen

Development and yield of spring wheat in water culture as influenced by nutrient concentration. The development of spring wheat cv. Solo grown until maturity in nutrient solutions of normal concentration changed weekly, differs from similar plants growing in soil. In experiments in which nutrient supply was reduced at different growth stages, an attempt was made to minimize the differences. These consist mainly of permanent tillering, retarded senescing of leaves and in dry matter accumulation in the grain. 1) Reducing the total nutrient supply during the grain filling period decreases the chlorophyll-con-tent of the flag-leaf at an earlier stage and hence also its ability to assimilate CO₂. This reduction in nutrient supply has thus a beneficial effect on the development of the grain by allowing a better coordination with leaf senescence and an increase in nitrogen and dry matter transfer from the flag leaf to the grain. 2) The retarded response to a reduction of the nutrient concentration points to a “luxury consumption” in the vegetative phase. This might be the reason why it was not really possible to achieve optimal timing of vegetative and generative development. 3) After examination of the effect of lowering the nutrient supply in the vegetative phase, a nutritional design for growingspring wheat in water culture was proposed. This consists of lowering the concentration to meet the needs of plants and comprises a rise and fall of the concentration (0.25,0.5, 0.75,0.5 and 0.25 of the normal conc., see fig. 4). 4) Comparing 0.4 and 0 mMol/l N during the grain filling(other nutrients supplied according to the concept outlined above), the relevance of nitrogen for the CO₂,-assimilation capacity and more obviously for the senescence of the flag leaf was shown. Nitrogen deficiency decreases the assimilation ability within a short time and depresses grain development. These findings confirm the validity of the nutritional concept proposed.     

Mobilität und Pflanzenverfügbarkeit von Phosphor aus organischen und anorganischen Formen in der Rhizosphäre von Lolium perenne

Mobility and availability of phosphorus from organic and inorganic forms in the rhizosphere of Lolium perenne 1.) In pots (sandwich-technique according to Helal and Sauerbeck), where the soil (A_p-horizon of an Alfisol-Udalf from loess) was separated into a root chamber and an outer chamber (up to 10 mm away from the root chamber), the phosphorus (P) availability of super-P, rock-P (Hyper-P) and organic P [myo-inositol-2-mono-P di(cyclohexylammonium) salt] was studied. P was applied at a rate of 50 mg P kg^?1 soil only in the outer chamber. This P fertilization resulted in significant increase of CAL- and water-extractable P in the treatment with organic P and super-P compared to the P₀ treatment. During 6 cuts of Lolium perenne organic P showed the same effect on the P-uptake of plants as super-P. Compared to the treatment without P, rock-P had no effect on the P-uptake. The higher P-uptake of Lolium perenne both in the super-P- and organic P-treatment was reflected at the end of the experiment only by the CAL-P content differences between root chamber and outer chamber. The highest activity of acid phosphatase, measured in air dried soil was found in the root chamber of the organic P treatment The content of EUF extractable organic P was significantly higher in the root chamber of the treatments with super-P and organic P than in the P₀- and rock-P-treatment. 2.) The P elution was studied with 2 soils (A_p-horizon of an Alfisol-Udalf from loess pH: 6.4; A_h-horizon of a basaltic brown soil pH: 5.4) under lab conditions in columns. In the super-P-and organic P-treatment leached P was mainly inorganic. In the soil with low pH value (5.4), P was leached in the treatment with super-P or organic P in a higher amount of organic P than in the soil with pH 6.4. The results of this experiment do not show in which form the applied organic P was moved to the roots or displaced in the soil.     

Varietal differences in accumulation of ochratoxin a in barley and wheat cultivars after inoculation of Penicillium verrucosum

The natural content of ochratoxin A in grain samples of 6 barley, 2 bread wheat and 1 durum wheat cultivars varied from <0.1 to 0.4 ng/g grain. Samples of the analysed cultivars were surface sterilized and kept in humidity chambers at 20°C and water activity (a_w) 0.75 or a_w 0.85 for 8 days. For both environments, the resulting grain equilibrium water content varied between cultivars of both barley and wheat, attributable to agronomic traits. The samples were then inoculated with Penicillium verrucosum and incubated for up to 23 weeks. With time, all cultivars had increasing ochratoxin A content, with maximum content in different barley cultivars ranging from 34 to 630 ng/g grain for a_w 0.75, and 39 to 260 000 ng/g for a_w 0.85. Corresponding values for the wheat cultivars were 25 to 2 300 ng/g and 650 to 5 200 ng/g. Significant varietal differences in ochratoxin A accumulation were observed for barley (P < 0.0001), attributable to equilibrium water content, amylose content and natural ochratoxin A, and for wheat (P < 0.0001), attributable to protein content and natural ochratoxin A. Barley ‘SW 1306 95/1203’ and ‘SW 906129 Waxy’, and wheat ‘SW 39103’ accumulated significantly less ochratoxin A than the other cultivars.     

Einfluß variierter Mg-Ernährung auf Tausendkorngewicht und P-Fraktionen des Gerstenkorns

Influence of varying Mg supply to barley on thousand grain weight and the P fractions of grains By variation of the Mg concentration in the nutrient solution (0.2; 0.6 and 1.8 me Mg/l respectively) during tillering, shooting and grain filling it could be shown, that increasing Mg supply to barley especially favours number of ears/plant (tillering) and grain size (thousand grain weight, TGW). A positive correlation was found between Mg content of grain and TGW. In small grains, which had a Mg content of 0.06% Mg in DM, about 64% of grain-P was present as Phytin-P and 20% as inorganic P. In bigger grains being also higher in Mg content, however, 70% was Phytin-P and only 10% P_i. This change in the pattern of P-fractions due to the Mg nutrition might be of a certain relevance to the regulation of starch synthesis within the grain and accordingly of grain growth.     

Cu‐, Zn‐ und Cd‐Aneignungsvermögen von zwei Spinatgenotypen in Abhängigkeit von der P‐Versorgung und Wurzelexsudation

Cu, Zn, and Cd acquisition by two spinach cultivars depending on P nutrition and root exudation Within a spectrum of 11 spinach cultivars (cvs) differences in the Cu, Zn, and Cd contents of shoots had been noticed. The aim of this study was therefore to analyze in more detail the acquisition of Cu, Zn, and Cd by the most differing cultivars (Tabu and Monnopa) in dependence on P nutrition. The plants were grown in a low phosphorus Luvisol (pH 6.3; total contents Cu: 89, Zn: 297, Cd: 2.4 mg kg^—1) with two phosphorus levels in pots under natural conditions. For the determination of inflow, root length/shoot weight ratio and of the Cu, Zn, and Cd concentration in the soil solution (rhizosphere) plants were harvested 26 and 40 days after sowing. Root exudation of organic acids of the two cvs was measured 35 days after growing in quartz sand with different P supply. Both cultivars responded to P fertilizer by doubling their shoot weight. With increased P supply (0.68—0.77% P in shoot‐DM) both cultivars showed similar heavy metal contents in the shoot resulting from similar root length/shoot weight ratios (RSR) and net uptake rates of the three elements as well as the same element concentrations in the rhizosphere soil solution. Under P deficiency, however, cv. Tabu (0.52% P in shoot‐DM) showed in comparison with cv. Monnopa (0.48% P) higher Cu, Zn, and Cd contents of shoots although its RSR was smaller than that of cv. Monnopa. However, the inflow for Cu was higher and for Zn and Cd significantly higher compared with cv. Monnopa. This result of cv. Tabu corresponded with higher concentrations of Cu, Zn, and Cd of its rhizosphere soil solution, and its higher exudation rates of oxalate, citrate, and malate (3.9; 1.0; 0.7 nmol cm^—1 h^—1). The corresponding values for cv. Monnopa were: 1.7; 0.3; 0.4 nmol cm^—1 h^—1. The mobilization of Cu, Zn, and Cd by the excreted organic acids seems to be responsible for the higher Cu, Zn, and Cd inflow of cv. Tabu.     

Einfluß der P-Aufnahme und P-Remobilisierung in der Kornfüllungsperiode auf den Ertrag von Sommerweizen

Influence of P-uptake and P-remobilization during the grain-filling period on the yield of spring wheat Experiments were performed with spring wheat in hydroponics using labelling with ³³P and ³²P to investigate the influence of high (0,5 mM) or low (0,05 mM) P-concentration in the solution on the distribution and remobilization of the nutrient as well as on crop yield. With low P-supply the yield was reduced, not only due to a considerable decrease of tillers but also in consequence of lowering the thousand grain weight and the number of grains even in apparently still fully developed ears, as well as significantly depressing the P-concentration in the grain. Flowering and maturity commenced much earlier than in the case of plants supplied with a relatively high level of phosphorus. When the P-concentration in the medium was only dropped from a high to low level after the end of flowering, the yield of the plants, which had a comparable number of tillers to the control, was slightly but significantly reduced, too. In spite of an enormous enhancement of the retranslocation of P deposited in the plant before flowering the P-concentration of the grain was also deminished. The experiments have shown that the intensified P-retranslocation during the grain-filling period and a still continuing P-uptake and translocation into the leaves and particularly the grain proceeded simultaneously under the experimental conditions. Besides, the effective P-retranslocation based on the labelling was substantially greater than indicated by the net P-retranslocation. The possible function of phosphate during the storage phase of cereals is discussed.     

Identifizierung und Bestimmung einiger Gibberelline und der Einfluß von Chlorcholinchlorid (CCC) auf das Gibberellinspektrum der einzelnen Getreidearten

Identification and determination of some gibberellins in the gibberellin spectrum of some cereals, als affected by CCC treatment The gibberellin contents of wheat, barley and oat plants, treated with CCC, were studied during the vegetative period. It was possible to identify a characteristic gibberellin spectrum for every cereal plant examined, although the variation was in a limited number of gibberellin forms. A great variation in the content of individual gibberellic acid forms was noticed, as well, among the different cereals studied. The highest content of gibberellins was found with GA₃. The content of GA₅ was lower than that of GA₉ while was not generally higher than that of GA₈. CCC-treated cereal plants showed lower values of gibberellins when compared with those of control. On the other hand, CCC treatment did not affect the content of gibberellins in the spikes which showed a considerably high content of GA₃, GA₅ and GA₉. A higher content of GA₇ was observed in both barley and oats, but not in the case of wheat, during tillering stage. However it was difficult, from the results of the present work, to indicate whether GA₇ is reponsible for the week effect of CCC obtained with both barley and oats or not.     

Einfluß von K-Ernährung und Mehltaubefall auf den N-Haushalt von Sommergerste während des Kornwachstums

Influence of K nutrition and mildew attack on N metabolism of spring barley during grain development Spring barley cv Aramir was grown in complete nutrient solutions containing 0,4 (K₁) and 4 me K/l (K₂) respectively. Half of the plants were sprayed regularly with a fungicide, the other half became naturally infected by mildew, Erysiphe graminis. Mildew attack was clearly visible in unsprayed plants, especially at K₁. Accordingly also grain yield was depressed by 18% (K₁) and 15% (K₂) compared to the controls. Better K nutrition reduced symptoms of mildew infection drastically and increased grain yield from 87 g/pot (K₁) to 169 g (K₂). Similar yield increases (106 to 199 g/pot) were obtained in the control plants, revealing that under the experimental conditions better K supply stimulated growth in general rather than inducing specific defense mechanism against the pathogen. The latter was hoped to be detectable by applying ¹⁵N-nitrogen during 3 days at anthesis. Although K₂ plants absorbed more ¹⁵N and incorporated more ¹⁵N into leaf protein, this cannot be considered as a K induced defense reaction. Instead due to lower grain yields in infected plants less proteolysis in the vegetative plant parts occured.     

Der Mangan-Gehalt von Getreide,Mais und Rüben als Anzeiger der Bodenversauerung

Manganese content of cereals, maize and beet as indicator of soil acidity Soil and plant samples with and without growth depressions were taken from 479 agricultural fields (sand - loam) in the former GDR and analysed for pH and Mn and Mg respectively. Depressions in growth accompanied with symptoms of Mn excess and sometimes also of Mg deficiency were observed for barley, wheat, oats, maize and beets at soil pH < 4, 7, for rye at pH < 4, 1 - 4, 4. Soil pH correlated highly negatively with the Mn concentration of plants in early growth stages. Thus toxicity levels of Mn concentration in young plants could be derived. Mn concentrations > 140 mg/kg dry matter in spring barley, > 150 mg/kg in winter barley, > 160 mg/kg in wheat, > 200 mg/kg in rye, > 300 mg/kg in oats, > 350 mg/kg in maize and > 800 mg/kg in beet indicate growth depressions because of soil acidity. In the case of simultaneous Mg deficiency these Mn values are lower for oats and rye.     

Pflanzenverfügbarkeit der Phosphatvorräte ackerbaulich genutzter Böden. -Langfristige Feldversuche zur Nutzbarkeit des Bodenphosphors und zur Bewertung der Bodenuntersuchung -

Availability of Phosphate Reserves in Arable Soils - Long Term Field Experiments for Assessing Soil P Reserves and Critical Soil Test Values - The objective of this work is to quantify the plant availability of soil P reserves accumulated by former fertilizer applications, the possibility of utilizing them by arable field crops and to determine critical soil test values. For this purpose several long term field experiments with large plots without replicates were initiated in 1977 on luvisols from loess (pH 6.8 – 7.4) in Lower Saxony with a sugar beet - winter wheat - winter barley/winter wheat crop rotation. Annual P applications were 0, 45, 90, 135 and 180 kg P₂O₅/ha as triple phosphate. Application of other fertilizers and plot management were according to farmer's practice. Despite of high yield levels phosphate response of plants was only 2 % at its maximum in the average of all crops in 15 years. This was confirmed by small plot experiments with four replicates placed into the large plots after 9 years, when soil P levels had been differentiated under the influence of plant P removal and P application. Herewith in agreement, shoot P concentration was found within the range generally regarded sufficient. It is therefore concluded that plant P demand has been fully satisfied by soil P reserves. Soil P test values, monitored by the P(H₂O) method of Sissingh, decreased markedly in 15 years, when no P was applied, they remained approximately constant when P application was equal to P removal and they increased when P addition was higher than P removal. Plants on a site with 4 mg P(H₂O)/L initially had severe P deficiency. Maximum yield was obtained when the soil P level was raised to 11 mg P(H₂O)/L. It is concluded that P reserves, which are often high in German arable soils, can be utilized by field crops and thus be lowered to about 10 mg P(H₂O)/L by reducing or omitting P dressings. For practical purposes it is suggested to restrict P application, if necessary at all, to the sugar beet crop in the rotation because they often respond more than small grain.     

磷素子粒生产效率不同品种的小麦磷素吸收利用差异

盆栽试验研究了130份小麦不同生育时期的干物重、磷素含量、子粒产量等指标,采用组内最小平方和的动态聚类方法将供试品种按磷素子粒生产效率从低到高依次分为Ⅰ、Ⅱ、Ⅲ、Ⅳ、Ⅴ和Ⅵ 6个类型,研究不同类型磷素吸收利用的差异。结果表明: 1）供试品种的磷素子粒生产效率差异较大（CV=1660%）,Ⅰ、Ⅱ、Ⅲ、Ⅳ、Ⅴ和Ⅵ类品种的平均磷素子粒生产效率为P 13629、15167、16916、18589、20132、24466 g/g。子粒产量随磷素子粒生产效率提高呈增加趋势（r=03203**）。2）不同生育时期,小麦植株磷浓度与吸磷量类型间差异显著或极显著。成熟期磷素子粒生产效率与植株磷浓度极显著正相关（r=06969**）,子粒产量与抽穗期、成熟期植株吸磷量显著或极显著相关（r=02966*、r=09271**）。3）不同生育时期磷素干物质生产效率的类间差异均达显著水平; 成熟期磷素干物质生产效率与磷素子粒生产效率极显著正相关 （r=07391**）。4）拔节期、抽穗期和成熟期干物重均表现出随磷素子粒生产效率增加而增加的趋势,成熟期尤为突出。拔节期成熟期磷素吸收量是影响子粒产量形成的重要因素,磷素子粒生产效率高的品种在拔节期后有较强干物质和子粒产量形成能力。     

Einfluß steigender Stickstoffgaben auf den Kupferernährungszustand von Getreide

Effect of increasing nitrogen fertilization on copper demand in cereals Pot experiments were conducted with wheat (2 experiments) and spring barley (1 experiment) in a peat soil. Four N and four Cu fertilizer levels were chosen in such a way that, based on grain yield, within each N level there was a Cu deficient and a Cu sufficient treatment. For sufficient Cu supply, Cu level in soil and plant increased with increasing N level. Critical Cu concentrations in aboveground biomass at shooting [μg (g dw)^?1] were 3.5 (lowest N level = N₁) to 7.5 (highest N level = N₄) for grain production of wheat and barley, but for aboveground biomass of wheat at shooting they were only 2.6 (N₁) to 5.8 (N₄). Based on critical Cu concentration at different N levels, critical Cu/N ratios were determined. These were independent from N level, indicating that Cu remobilization in the older leaves is unlikely even at N deficiency. The high critical Cu concentrations at high N levels may be explained by an increased immobilization of Cu. Under Cu deficient conditions, Cu concentration did not increase with increasing N level. However, under Cu sufficient conditions, N concentration and Cu concentration of the plant increased with increasing N level. The increasing Cu uptake with increasing N level may be explained by the release of amines into the root apoplast and the rhizosphere. Particularly under Cu sufficient conditions, these may mobilize Cu by formation of soluble Cu-amine complexes.     

Senescence of the flag leaf and grain yield following late foliar and root applications of phosphate on plants of differing phosphorus status

The balance between leaf senescence, induced by phosphorus deficiency, and grain growth was examined in wheat plants grown in sand with high (control) and low phosphorus (low‐P) nutrition. Foliar applications of P were made prior to anthesis and at early and mid grain development. Low‐P plants were also given an additional dose of P via the roots at mid grain development.

Foliar applications of P had no effect on leaf function (net CO₂ exchange rate), or grain development in control plants. However, P applied to the flag leaf of low‐P plants delayed senescence and thus increased leaf area duration, but this did not result in a significant increase in grain yield per ear. Phosphorus applied to the ear surface (the glumes) of low‐P plants increased the concentration of P in the grain, but did not increase the number of cells per grain, or the grain yield per ear. The late application of P via the roots also delayed senescence in low‐P plants, but did not cause an increase in yield.

These experiments indicate that grain growth in low‐P plants is not limited by the level of supply of photosynthate, or the availability of P during the actual period of grain development. Phosphorus translocated to the grain late in plant development is used inefficiently in plants that are adequately supplied with phosphorus and in plants suffering from P deficiency.     

Effect of phosphoric fertilizer and starter rates of nitrogen fertilizers on the phosphatase activity in the rhizosphere soil and nonlignified soybean roots under drought conditions

In a small-plot field experiment, two soybean (Glycine max L.) cultivars were grown on a calcareous chernozem under the drought conditions of 2012 with the preplanting application of simple superphosphate (P_s) at 60 kg/ha, urea (N_u) at 10 and 20 kg/ha, and ammonium nitrate (N_an) at 20 kg/ha. The phosphatase activity was measured in the rhizosphere soil (0- to 20-cm layer) and the fine nonlignified roots of soybean plants at the blossoming and pod-formation stages (the soil water content was 19 and 33% of the total water capacity, respectively). The maximum content of available phosphorus in the rhizosphere of both soybean cultivars (4.3–4.8 mg/100 g dry soil) was found at the simultaneous application of P_s and N_u20. Higher activities of the predominant phosphatases (alkaline phosphatase in the rhizosphere and acid phosphatase in the roots) were observed in the root-inhabited zone of the soil under the Indra cultivar compared to the Aura cultivar, which correlated with the lower content of available phosphorus in the rhizosphere soil (especially at the simultaneous application of P_s and N_u20) and the higher productivity of this cultivar in this treatment.     

The changes in physiological and biochemical traits of Tibetan wild and cultivated barley in response to low phosphorus stress

Low phosphorus (LP) limits crop growth and productivity in the majority of arable lands worldwide. Here, we investigated the changes in physiological and biochemical traits of Tibetan wild barleys (Hordeum vulgare L. ssp. spontaneum) XZ99 (LP tolerant), XZ100 (LP sensitive), and cultivated barley ZD9 (moderately LP tolerant) under two phosphorus (P) levels during vegetative stage. These genotypes showed considerable differences in the change of biomass accumulation, root/shoot dry weight ratio, root morphology, organic acid secretion, carbohydrate metabolism, ATPase (Adenosine triphosphatase) activity, P concentration and accumulation under LP in comparison with CK (control) condition. The higher LP tolerance of XZ99 is associated with more developed roots, enhanced sucrose biosynthesis and hydrolysis of carbohydrate metabolism pathway, higher APase (Acid phosphatase) and ATPase activity, and more secretion of citrate and succinate in roots when plants are exposed to LP stress. The results prove the potential of Tibetan wild barley in developing barley cultivars with high tolerance to LP stress and understanding the mechanisms of LP tolerance in plants.     

Einfluß der Lichtintensität bei variierter Kaliumernährung auf CO2-Assimilation und Ertragsbildung bei Sommerweizen

Effect of light intensity at varied potassium supply on CO₂ assimilation and yield formation of spring wheat .

• 1 The effect of a varied K⁺ supply on CO₂ assimilation rates and yield formation has been studied at two different light intensities with wheat (Triticum aestivum L.) grown in solution culture. Light intensity was reduced in one treatment by shading the plants with a cloth, which caused a reduction of about 50 % of the light intensity. This shading was applied from the heading stage until grain maturation.
• 2 Reduced light intensity resulted in remarkably decreased rates of dry matter increments in both K treatments. In the beginning this growth depression, however, was small in the treatment with the higher K supply. At the stage of transition from the vegetative to the reproductive stage the better K⁺ nutrition obviously could compensate the lacking light to some degree. This favourable K⁺ effect, however, decreased with the advance of the reproductive phase. Thus at maturation in both K treatments equal quantities of dry matter were harvested. In the treatments with full light the higher K supply resulted in a yield increase at maturation.
• 3 The CO₂ assimilation rates measured at flowering, milk stage and dough stage indicated that rather the K supply than the light intensities influenced the CO₂ assimilation. The treatments with the higher K supply showed almost twice as high assimilation rates compared with the treatments with the lower K supply.
• 4 The reduced light intensity caused a substantial depression in grain yield in both K treatments. The poor grain yield was mainly due to a reduced thousand grain weight and to a less extent to a reduction in the number of ears.
• 5 As the better K supply resulted in increased CO₂ assimilation rates without having an influence on the grain filling of the plants exposed to a lower light intensity, it is concluded that at low light intensities the grain filling is not limited by the supply of grains with photosynthates but probably is affected by other processes.

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Aufnahme und Verlagerung von 15N-Stickstoff bei Sommergerste in Abhängigkeit von K-Ernährung und Mehltaubefall

¹⁵N uptake and distribution by spring barley in relation to K nutrition and mildew attack Barley cv. Aramir was grown in complete nutrient solution containing 0,5 (K₁), 1,5 (K₂) and 4,5 mM K (K₃) respectively till maturity. Part of the plants was infected by mildew (Erysiphe graminis), whereas control treatments were kept mildew-free by fungicide sprays. Symptoms of mildew attack were less at K₂ and K₃ and grain yields of infected plants were raised from 98 (K₁) to 160 (K₂) and 165 g/pot (K₃). In control treatments grain yields were 130 (K₁), 164 (K₂) and 163 (K₃) g/pot. During anthesis nitrogen in the nutrient solution was labelled with ¹⁵N for two days and ¹⁵N metablism was studied within 7 consecutive days. The aim of this pulse-chase experiment was to find out, how mildew attack and K nutrition influence N metabolism. The following results were obtained: a) ¹⁵N uptake increased from K₁ to K₂ in infected and healthy plants, though at slightly lower levels in the infected treatments. b) During 7 days after the ¹⁵N pulse up to 17,1% of the ¹⁵N absorbed were translocated into the grains. Better K status as well as spray treatments stimulated nitrogen translocation. c) Mildew attack of leaves does not seem to influence the conversion of grain-¹⁵N into grain proteins. Better K supply stimulates the rate of protein synthesis in the grain. d) In mildew infected leaves relatively more of the ¹⁵N absorbed is incorporated into leaf proteins. But this may be a consequence of slower grain growth, because already 7 days after anthesis infected plants in all K treatments had significantly lower grain yield. In spite of the short duration of the experiment the ¹⁵N data do not indicate that the visible depression of mildew attack by better K nutrition of the crop might inter alia be due to K stimulated defense reactions within N metabolism. This is in agreement with a previous experiment.     

CELL WALL URONIC ACID CONCENTRATIONS OF RESISTANT AND SENSITIVE CULTIVARS OF WHEAT AND BARLEY UNDER BORON TOXICITY

In this study, changes in cell wall uronic acid concentrations of boron (B)-tolerant and B-sensitive cultivars of wheat and barley were analyzed in control (plants that were grown on water and received no B) and B-treated plants. Ten-day-old seedlings of wheat (Triticum aestivum L. ‘Atay’ (B-sensitive) and ‘Bolal’ (B-tolerant)) and barley (Hordeum vulgare L. ‘Hamidiye’ (B-sensitive) and ‘Anadolu’ (B-tolerant)) were grown in H₃BO₃ solution (10 mM final concentration) or water for 3, 5, or 7 days. For determination of changes in cell wall uronic acid concentrations of wheat and barley cultivars, cell walls were extracted from root and leaf tissues of control and B-treated plants. Cell wall uronic acid concentrations of root and leaf tissues of each cultivar were statistically analyzed. Various reciprocal analyses were performed. These analyses were high-B-tolerant versus B-sensitive cultivars and control versus B-treated plants. In all reciprocal analyses, no significant changes were observed. These data, thus, suggest that cell wall uronic acid content does not contribute to detoxification of excess B in wheat and barley.