Jóska Gerendás

Significance of nickel for plant growth and metabolism

Ni is the most recent candidate to be added to the list of 13 essential mineral elements for higher plants although failure to complete the life cycle in the absence of Ni has only been demonstrated in a few plant species. Ni is considered an essential element primarily because of its function as an irreplaceable component of urease which is responsible for the hydrolysis of urea N, and which seems to be the only proven nutritional function of Ni in higher plants. For production of full urease activity and growth on urea N a critical deficiency level of around 100 μg kg—1 DW seems appropriate, while plants depending on mineral N may have a lower Ni requirement. Ni has also other effects on plant growth, of which the phytosanitary action is possibly most significant in the field. The incorporation of Ni into urease apoprotein requires the active participation of several accessory proteins, and mutations in genes coding the accessory proteins as well as the urease apoprotein have been exploited to characterise aspects of urease activation. The mobility of Ni within the plant, as compared to other heavy metals, is usually high, although little is known of the uptake mechanisms and the form of transported Ni under Ni-deprived conditions. This as well as other effects of Ni that cannot be related to its structural component of urease, remain to be elucidated. Die Bedeutung von Nickel fur das Wachstum und den Stoffwechsel von Pflanzen Ni ist der jungste Kandidat fur die Liste der bisher 13 essentiellen mineralischen Nahrelemente hoherer Pflanzen, obwohl der Beweis fur seine Notwendigkeit zur Vollendung des Lebenszyklus einer Pflanze erst bei wenigen Arten gelang. Die Essentialitat von Ni begrundet sich insbesondere auf dessen Funktion als unersetzlicher Bestandteil des Enzyms Urease, welches die Hydrolyse von Harnstoff katalysiert. Dies ist die bislang einzige nachgewiesene Funktion von Ni in der hoheren Pflanze. Hinsichtlich des Wachstums harnstoffernahrter Pflanzen und der Ureaseaktivitat konnte ein kritischer Gehalt von etwa 100 μg kg—1 TM abgeleitet werden, wahrend Pflanzen, die mineralischen N erhalten, einen wesentlich geringeren Ni-Bedarf haben. Ni hat noch weitere Effekte auf das Pflanzenwachstum, von denen die phytosanitaren Wirkungen unter Feldbedingungen sicherlich die wichtigsten sind. Der Einbau von Ni in die Ureaseapoproteine erfordert die aktive Beteiligung mehrerer akzessorischer Proteine und Mutationen der Gene, die diese akzessorischen Proteine und die Ureasestrukturgene kodieren, wurden erfolgreich zur Aufklarung zahlreicher Aspekte der Ureaseaktivierung eingesetzt. Die innerpflanzliche Mobilitat von Ni ist, verglichen mit anderen Schwermetallen, normalerweise relativ hoch, doch liegen nur wenige Informationen uber die Ni-Aufnahme und transportierten Ni-Spezies bei niedrigem Ni-Angebot vor. Diese und andere Aspekte der Ni-Ernahrung, die nicht auf dessen strukturelle Bedeutung in der Urease zuruckgefuhrt werden konnen, harren ihrer Untersuchung.

Impact of nitrogen supply on carbon/nitrogen allocation: a case study on amino acids and catechins in green tea [Camellia sinensis (L.) O. Kuntze] plants.

The concentrations of free amino acids (AA) and polyphenols (PP) are important determinants of green tea quality. Levels of AA and PP are governed interactively by nitrogen (N) supply and carbon (C) status, so the impact of C/N allocation on green tea quality was investigated in saplings cultivated hydroponically with 0.3, 0.75, 1.5 or 4.5 mmol l(-1) N. Activities of glutamine synthetase (GS), phenylalanine ammonia lyase (PAL), and phosphoenolpyruvate carboxylase (PEPC) were determined, as were concentrations of AA, PP and soluble sugars. Concentrations of AA increased with increasing N supply, and the AA profile was shifted towards AA characterised by low C/N ratios (arginine, glutamine) and away from theanine, the unique non-protein AA that is abundant in Camellia sinensis. High N supply significantly reduced the concentrations of PP in young shoots, and was accompanied by lower levels of carbohydrates (soluble sugars). Analysis of the C and N status and selected enzyme activities, combined with path coefficient analysis of variables associated with C and N metabolism, demonstrated increasing deviation of C flux to AA under abundant N supply. Accumulation of AA and PP depended strongly on N status, and the balance shifted toward increasing synthesis of AA associated with enhanced growth, while investment of C in secondary metabolites did not change proportionally under the condition of ample N supply.

The significance of magnesium for crop quality

BackgroundThe quality of agricultural and horticultural products and its modulation by fertilization has increasingly received attention. However, whereas the importance of magnesium (Mg) as an essential plant nutrient is well established, the impact of Mg nutrition on quality parameters has only been rarely addressed.ScopeThis review aims at evaluating the available knowledge on the influence of Mg on produce quality. A short discussion on the term quality as used in this review is followed by an overview of the various functions of Mg in plant metabolism in relation to quality aspects. Finally, the available literature on Mg-associated effects on crop quality is critically surveyed. The question whether Mg application beyond yield optimum further improves crop quality is specifically addressed.ConclusionIncreasing Mg supply on Mg-deficient sites tends to increase the quality of agricultural crops, particularly when the formation of quality traits is dependent on Mg-driven photosynthesis and assimilate translocation within the plant. In fruits and vegetables, ratios of Mg to other nutrients like Ca and K were shown to be a more reliable indicator of the quality response than the Mg status alone. Moreover, it is concluded that Mg doses beyond those required for maximum yield rarely induce a further improvement of produce quality.

Influence of Nitrogen and Potassium Supply on Contents of Acrylamide Precursors in Potato Tubers and on Acrylamide Accumulation in French Fries

ABSTRACT Fried potato products may accumulate substantial amounts of acrylamide due to high precursor contents, namely reducing sugars and asparagine. In a two-factorial experiment increasing N supply, increased the contents of reducing sugars in most cases, and resulted in higher contents of free amino acids. α -amino-N, which was tightly correlated with the contents of free amino acids, can be regarded a suitable rapid test for free asparagine for a given variety. Increasing K addition always raised the citrate contents, but lessened the contents of reducing sugars. Selected treatments were processed into French fries. Highest acrylamide contents were observed in tubers grown with high N and inadequate K supply, which also contained the highest contents of precursors. The experiment clearly demonstrates that nutrient supply has significant impact on the contents of acrylamide precursors and thus for the acrylamide formation during frying.

Effects of Nitrogen and Sulfur on Total Phenolics and Antioxidant Activity in Two Genotypes of Leaf Mustard

ABSTRACT Leaf mustard (Brassica juncea Coss) is widely used for both fresh and processed markets in southern China. It contains high nutritional and medicinal compounds, which are important for maintaining optimum health. The objective of this study was to determine the influence of nitrogen (N) and sulfur (S) nutrition on total phenolics and antioxidant activity in two genotypes of leaf mustard (cvs. ‘Xuelihong’ and ‘Zhujie’). Plants were greenhouse-grown using nutrient solutions with two levels of nitrogen (10 and 25 mM) and three levels of sulfur (0.5, 1, and 2 mM). Total phenolic concentrations were considerably decreased by increasing nitrogen supply, whereas increased by increasing sulfur supply. Total phenolic concentrations in cv ‘Zhujie’ was higher than in cv ‘Xuelihong’. Three assays including 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity, β -carotene bleaching (BCB), and ferric reducing antioxidant power (FRAP) were used to evaluate antioxidant activity. Increasing nitrogen supply reduced DPPH radical scavenging activity and FRAP value, but increased antioxidant activity using BCB assay. Increasing sulfur supply increased antioxidant activity with all three tests. The effects of genotype on DPPH radical scavenging activity and FRAP value were not significant, however, antioxidant activity using BCB assay was significantly higher in cv ‘Zhujie’ than in cv ‘Xuelihong’. A significantly positive correlation was found between DPPH radical scavenging activity and total phenolic concentrations in two genotypes, FRAP value and total phenolic concentrations in cv ‘Xuelihong’.

Effect of N concentration and N source on root colonization by Pseudomonas fluorescens 2-79RLI

Wheat (Triticum aestivum L.) was grown in nutrient solution with low or high N supply (NH4NO3 as N source). To further evaluate the influence of N form and its interaction with the nutrient solution pH, wheat plants were grown with NH4+ or NO3- either in an conventional nutrient solution or in a nutrient solution in which the pH was maintained at pH 6.5 using a pH-stat system. The nutrient solution was inoculated with Pseudomonas fluorescens 2-79RLI, a genetically modified bacterium that contains lux genes activated by a ribosomal promoter. Cell numbers and physiological status of P. fluorescens 2-79RLI (length of the lag phase of bioluminescence) in the rhizosphere were determined at the root tip and in the lateral root zone. Nitrogen deficiency decreased both plant growth and root colonization by P. fluorescens 2-79RLI at the root tip while it had no effect on root colonization in the lateral root zone. The physiological status of P. fluorescens 2-79RLI was not affected by nitrogen deficiency. Ammonium nutrition increased root colonization by P. fluorescens 2-79RLI at the root tip and in the lateral root zone when the pH of the nutrient solution was allowed to change according to the N form provided. Under these conditions, the physiological status of P. fluorescens 2-79RLI was higher in the lateral root zone than at the root tip. In contrast, N source had no effect on root colonization or physiological status of P. fluorescens 2-79RLI in the nutrient solution maintained at pH 6.5. It is concluded that the stimulation of root colonization by NH4+ in the nutrient solution, not maintained at a constant pH, may be due to increased leakage of solutes into the rhizosphere as a result of impaired exudate retention by high H+ concentration in the rhizosphere or the apoplast.

The influence of nitrogen and potassium supply on the ammonium content of maize (Zea mays L.) leaves including a comparison of measurements made in vivo and in vitro

Maize seedlings were grown on either nitrate or ammonium, at two different potassium levels, and the growth analysis revealed that ammonium supply reduced shoot dry matter particularly under conditions of limited potassium supply. The ammonium content of the leaves was determined in vitro, using continuous flow analysis of plant extracts, and in vivo using 14N nuclear magnetic resonance (NMR) spectroscopy. The conventional continuous flow analysis procedure was modified by the inclusion of a gas dialysis step across a PTFE membrane and control experiments showed that this provided an effective method for avoiding the overestimation of the ammonium content of leaf tissue extracts, by eliminating interference from amino acids and amides. Excellent agreement was obtained between the non-invasive NMR method and the modified continuous flow analysis technique, and it was concluded that leaf ammonium levels are unlikely to affect growth in plants grown with an adequate potassium supply.

Relationship between intracellular pH and N metabolism in maize (Zea mays L.) roots

In vivo31P nuclear magnetic resonance (NMR) was used to characterize the effect of the N form (NO3 vs. NH4) and the external pH (4, 6, and 8), on the intracellular pH of root tips (0–5 mm) and root segments (5–30 mm). Ammonium-grown root tips were the most sensitive to changes in the external pH. In vivo15N NMR was used to characterize the pathway of primary ammonium assimilation in the ammonium-grown roots and to compare the activity of the apical and more-basal root parts. The kinetics of 15NH4+ incorporation showed that primary assimilation in both root tips and root segments followed the glutamine synthetase (GS) pathway. In agreement with the reported gradient of GS along the seminal root of maize, incorporation of label into glutamine amide was more rapid in tips than in segments. It is suggested that this higher GS activity increases the endogenous proton production and thus contributes to the greater dependence of the cytoplasmic pH on the external pH in the ammonium-treated root tips.

Co does not replace Ni with respect to urease activity in zucchini (Cucurbita pepo convar. giromontiina) and soybean (Glycine max)

In order to evaluate whether Co can functionally replace Ni in urease, as suggested by Watanabe et al. (Soil Sci. Plant Nutr. (1994) 40, 545–548), zucchini and soybean plants were grown in purified nutrient solutions containing nitrate and ammonium as sole N source supplemented either with 0.05 mmol m-3 Ni or Co or with no supplementation (control). In addition, isolated soybean cotyledons were incubated axenically with either 1 mmol m-3 Ni or Co supplements. Plant growth was not affected by the Ni and Co additions, but urease activity was only detected in Ni-supplemented tissue, and in no case did Co raise the urease activity level. Only Ni-deprived plants (–Ni – Co and –Ni + Co) accumulated appreciable amounts of urea in the leaves. These results strongly suggest, that Co does not replace Ni with respect to functional urease.

Nitrogen use efficiency of safflower as compared to sunflower.

ABSTRACT This study compares the nitrogen (N) use efficiency of safflower and sunflower in pot experiments, as the putatively high nitrogen use efficiency of the former is not sustained. Safflower out-yielded sunflower at low N supply, while at ample supply the opposite was observed. Both species accumulated similar amounts of N per pot at equivalent N supplies, but safflower was a better N accumulator due to lower dry matter production. Safflower utilizes absorbed N more efficiently than sunflower to produce seed yield at suboptimal N supply in terms of efficiency ratio and utilization index, but the opposite holds true at optimal and high supply. Functional analysis of utilization efficiency for dry matter and seed production substantiated the higher efficiency of safflower. It is concluded that in terms of N utilization safflower represents a low input crop and outperforms sunflower with respect to seed yield on soils low in available N.