C and N utilization of two lettuce genotypes during growth under non-varying light conditions and after changing the light intensity

Growth and N-incorporation in two lettuce genotypes ( Lactuca sativa L. cv. Deci minor and cv. Grosse brune), which differ significantly in nitrate accumulation, were studied. Under constant environmental conditions cv. Deci minor produced more fresh and dry weight than cv. Grosse brune. Cultivar Deci minor also produced more fresh weight per mmol N absorbed than cv. Grosse brune, and contained less organic nitrogen in the dry matter, but accumulated more nitrate. As cv. Deci minor showed a higher fresh and dry weight production per mmol N absorbed than cv. Grosse brune, it used its nitrogen more efficiently.
When the light intensity was decreased, the growth of both cultivars decreased, and the fresh weight production per mmol N absorbed increased. After reduction of the light intensity, cv. Deci minor maintained a higher fresh weight production per N absorbed than before, whereas cv. Grosse brune returned to its original level. After decrease of the light intensity, an increased nitrate concentration in the cell sap was accompanied by a decreased concentration of organic compounds in both cultivars. The organic nitrogen level in the dry matter remained constant after the higher intensity was reduced. However, due to the decreased dry weight percentage, the demand for nitrogen for protein synthesis decreased on fresh weight basis.
It can be concluded that the two cultivars differ in their partition of C and N between dry matter and cell sap. Nitrate accumulation in preference to accumulation of organic compounds does not automatically result from a shortage of organic compounds. The high accumulation of nitrate of cv. Deci minor enables it to use more carbohydrates for structural growth than cv. Grosse brune.     

The Role of Nitrate in the Osmoregulation of Lettuce (Lactuca sativa L.) Grown at Different Light Intensities

Blom-Zandstra, M. and Lampe, J. E. M., 1985. The role of nitratein the osmoregulation of lettuce (Lactuca sativa L.) grown atdifferent light intensities.—J. exp. Bot. 36: 1043–1052. The effect of different light intensities on the nitrate accumulationvis-à-vis the concentration of other solutes in plantsap expressed from lettuce leaves was studied. After growinglettuce plants under constant environmental conditions for 52d, they were transferred to different light intensities andharvested periodically. A quantitative analysis of componentsin solution in the expressed plant sap showed a decrease innitrate concentration and an increase in the organic acids (mainlymalate) and sugars (mainly glucose) with increasing light intensity.The light intensity only slightly increased the osmolarity ofthe expressed plant sap. The measured osmolarity correspondedvery well with the value estimated from the quantitative analysesimplying that all osmotically active compounds had been accountedfor. The decrease in nitrate concentration in the expressedplant sap was fully compensated for by an increase in the dissociatedorganic acids that partly dissociate twofold to sustain electroneutralityand by an increase in both organic acids and sugars to maintainthe osmolarity. The suggestion is supported that nitrate mayserve as osmoticum at low light conditions to compensate forthe shortage of carbohydrates resulting from suboptimal photosynthesis. Key words: Nitrate accumulation, osmoregulation, Lactuca saliva L.     

Influence of plant nutrient concentration on growth rate: Use of a nutrient interruption technique to determine critical concentrations of N,P and K in young plants

A method is described for determining the way in which growth rate varies with plant nutrient concentration using a simple nutrient interruption technique incorporating only 2 treatments. The method involves measuring the changes in growth and nutrient composition of otherwise well-nourished plants after the supply of one particular nutrient has been withheld. Critical concentrations are estimated from the relationship between the growth rate (expressed as a fraction of that for control plants of the same size which remained well-nourished throughout) and the concentration of the growth-limiting nutrient in the plants as deficiency developed. Trials of the method using young lettuce plants showed that shoot growth rate was directly proportional to total N (nitrate plus organic N) concentration, and linearly or near-linearly related to K and P concentration over a wide range; the corresponding relationship for nitrate was strongly curvi-linear. Critical concentrations (corresponding to a 10% reduction in growth rate) determined from these results were similar to critical values calculated from models derived from field data, but were generally higher than published estimates of critical concentration (based on reductions in shoot weight) for plants of a similar size. Reasons for these discrepancies are discussed. Nitrate, phosphate or potassium concentrations in sap from individual leaf petioles were highly sensitive to changes in shoot growth rate as deficiency developed, with the slope of the relationships varying with leaf position, due to differences both in their initial concentration and in the rates at which they were utilized in individual leaves. Each nutrient was always depleted more quickly in younger leaves than in older ones, providing earlier evidence of deficiency for diagnostic purposes. Although the plants were capable of accumulating nitrate, phosphate and potassium well in excess of that needed for optimum dry matter production during periods of adequate supply, the rate of mobilization of these reserves was insufficient to prevent reductions in growth rate as the plants became deficient. This brings into question the validity of the conventional concept that luxury consumption provides a store of nutrients which are freely available for use in times of shortage. The implications of these results for the use of plant analysis for assessing plant nutrient status are discussed.     

Short- and long-term effects of a change in the spatial distribution of nitrate in the root zone on N uptake, growth and root development of young lettuce plants

Abstract. The effects of a change in the distribution of nitrate within the root zone on N uptake and growth were studied using young lettuce plants after reducing the proportion of their root systems supplied with nitrate from 100 to ca 10% in split-root experiments in the glasshouse. The main effects of the localized nitrate supply were concentrated in a 2-week period immediately after the treatment was imposed, when a temporary reduction in nitrate uptake caused the gradual development of N deficiency and a decline in plant growth rate. The plants adapted to the change in nitrate distribution, initially by increasing unit absorption rates (uptake rates per unit weight of root) and more gradually by increasing production of new roots in the high-nitrate zone. As a result, relative N uptake rates and relative growth rates were restored to the same levels as for control plants (given a spatially uniform N supply throughout) after ca 12d, even though only ca 12–15% of their roots were exposed to nitrate at this time. Thereafter, the plants continued to adapt by concentrating new root growth in the nitrate-containing zone, ultimately allowing unit absorption rates to return to normal. There was no evidence of any significant N deficiency in the plants after the initial adaptive response was complete, even though the total-N concentrations of the plants given the localized supply were consistently less than those given the uniform N treatment, and nitrate concentrations in the petiole sap were generally lower in leaves on one side of the plant (because of limited lateral movement of nitrate between xylem vessels during its transport to the shoot). The delay in the initiation of an adaptive response caused a significant check in growth, and the resulting relative weight differences were maintained throughout the subsequent life of the plant. Plants in all treatments matured on the same date, so yields for those grown with the localized supply were less than those of the control, and could not be recovered by delaying final harvest without unacceptable loss of quality. The pattern of the changes in N uptake and plant growth, and the effect on final yield, were similar to those exhibited by young lettuce plants subjected to a temporary interruption in nitrate supply, suggesting that the reduction in final yield for plants grown with the localized supply was largely the effect of the check in growth which occurred whilst the Plants were adapting to the change in nitrate distribution during the early part of the experiment. This implies that the rate of dry matter production of young lettuce plants can be altered by N treatment without affecting their rate of physiological development.     

A Mechanistic Theory for the Relationship between Growth Rate and the Concentration of Nitrate-N or Organic-N in Young Plants derived from Nutrient Interruption Experiments

A simple assumption about nitrate assimilation (incorporatinga single parameter to represent the conversion of nitrate intoorganic-N) has been used to derive mechanistic equations todescribe the interrelationships between the concentrations ofnitrate-N and organic-N, and dry weight for both the whole plantand its shoot in nutrient interruption experiments. These equationshave been combined with a logistic growth model, which was derivedfrom initial assumptions about the way in which plants use storedN under these conditions (Burns, 1994), to quantify effectsof nitrate-N and organic-N concentrations on relative growthrate. The models were tested by fitting equations for the predictedrelationships to data for young cabbage and lettuce plants,from which estimates of the N assimilation parameter were obtained.The tests showed that predictions of relative growth rate weregenerally in good agreement with the data over the whole range,as were those for the corresponding relationships between dryweight and either nitrate-N or organic N- concentration, andfor the interrelationships between the two forms of N. The mostreliable estimates of the N assimilation parameter were obtainedfrom relationships where nitrate-N concentration was the explanatory(independent) variable, because the fits of the correspondingrelationships with organic-N were relatively insensitive tolarge changes in its values. The results showed no evidenceof any consistent variation in the size of this N assimilationparameter with the nitrate status of the plant. However, smallbetween-crop differences in its value suggest that shoot nitratemay have been assimilated slightly more efficiently in cabbagethan in lettuce. The new model predicts that dry matter production is restrictedas soon as the external N supply is withheld (irrespective ofthe plant nitrate status), producing a slow but consistent declinein relative growth rate which is maintained until nitrate isalmost depleted, whereupon it falls rapidly. This implies thatthe rate of chemical reduction of stored nitrate was not sufficientto maintain an adequate supply of organic-N for the productionof new dry matter (even when its concentration in the plantsis still high). The results show that nitrate concentrationsin excess of 0·1 mmol g^-1 are required in plants to avoidserious reductions in growth rate when N is in short supply.Copyright1994, 1999 Academic Press Cabbage, concentration, deficiency, hydroponics, lettuce, model, nitrogen, nitrate, nutrient interruption, organic-N, relative growth rate, shoot, whole plant     

玉米氮素吸收的基因型差异及其与根系形态的相关性

采用溶液培养的方法,选用在田间、土培试验中对氮反应有典型差异的玉米自交系：478、H21、Wu312、Zong31、Baici,在4个供N水平（0.04、0.4、2.4mmol/L）下,研究了玉米苗期氮素吸收、分配的基因差异以及与根系形态之间的相关关系,结果表明：在一定的NO3^-浓度范围内（0.04-2mmol/L）,根系生物量随N水平的提高而增加,而高N不同程度地降低了5个自交系根系干重。低N下（0.04mmol/L）,与其它自交系相比,N高效基因型478具有较大的根系生物量,其根系干重分别为H21、Wu312、Zong31、Baici的1.1、1.74、1.6、1.18倍,并往根系分配了较大比例的N素,根系N累积占总N量的百分率比Wu312、Zong31分别高18.34％、17.08％,而N低效基因型Wu312、Zong31则往地上部分配了较大比例的氮素。随N水平的增加,显著促进了地上部的生长,并在地上部分配了较大比例的N素。当N水平增至4mmol/L时,地上部N素分配的基因型差异减小。低N下,5个自交系根系干重、总根长、根轴总长与总吸N量显著线性相关,而高N下不表现相关关系,说明在N素胁迫的条件下,根系形态对N吸收效率起重要作用。     

The influence of genetic variation and nitrogen source on nitrate accumulation and iso-osmotic regulation by lettuce

Background and aims

Characterisation of genetic variation in nitrate accumulation by lettuce will inform strategies for selecting low-nitrate varieties more capable of meeting EU legislation on harvested produce. This study uses a population of recombinant inbred lines (RILs) of lettuce to determine how genotypic differences influence N uptake, N assimilation and iso-osmotic regulation, and to identify key related traits prior to future genetic analysis.

Methods

Measurements were made on plants grown to maturity in soil fertilised with ammonium nitrate, and in a complete nutrient solution containing only nitrate-N. A simple osmotic balance model was developed to estimate variations in shoot osmotic concentration between RILs.

Results

There were significant genotypic variations in nitrate accumulation when plants were grown either with nitrate alone or in combination with ammonium. Ammonium-N significantly reduced nitrate in the shoot but had no effect on its relative variability, or on the ranking of genotypes. Shoot nitrate-N was correlated positively with total-N and tissue water, and negatively with assimilated-C in both experiments. Corresponding relationships with assimilated-N and shoot weight were weaker. Estimated concentrations of total osmotica in shoot sap were statistically identical in all RILs, despite variations in nitrate concentration across the population.

Conclusions

Approximately 73% of the genotypic variability in nitrate accumulation within the population of RILs arose from differences in nitrate uptake and only 27% from differences in nitrate assimilated, irrespective of whether or not part of the N was recovered as ammonium, or whether the plants were grown in soil or solution culture. Genotypic variability in nitrate accumulation was associated with changes in concentrations of other endogenous solutes (especially carboxylates and soluble carbohydrates) and of tissue water, which minimised differences in osmotic potential of shoot sap between RILs. This offers the opportunity of using the regulation of these solutes as additional traits to manipulate nitrate accumulation.     

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     

Storage of Osmotically Active Compounds in the Taproot of Daucus carota L.

The osmotic potential of cell sap from the storage root, lateralroots and shoots of carrot (Daucus carota L., cv. AmsterdamseBak) was calculated from the concentration of osmotically activecompounds in these tissues. The osmotic potential of the taprootdid not change with age prior to and during the storage of osmoticallyactive sugars, as sucrose and reducing sugars. The increased contribution of soluble sugars in the osmoticpotential was accompanied by a proportionally decreased contributionof potassium and organic acids. Before storage of soluble sugarsin the taproot occurred, potassium and organic acids contributed80% to the total osmotic value, in contrast with lateral roottissue, where potassium and nitrate were the main osmotic solutes.The concentration of osmotically active solutes was lower inlateral root tissue than in storage root tissue. Shoot tissueresembled taproot tissue before storage, in having potassiumand organic acids as the main osmotic solutes. The concentrationof osmotically active solutes was highest in shoot tissue andit increased towards the end of the experimental period. The calculated osmotic potentials were in good agreement withthe experimental values, as determined from the molecular depressionof the freezing point of cell sap. Storage of reducing sugarsand sucrose is discussed in relation to acid and neutral invertaseactivities. Key words: Daucus carota, Osmotic solutes, Sugar storage, Invertase activity     

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     

Effect of nitrogen form on the growth and nitrate concentration of lettuce

Summary A pot experiment with lettuce involving three N forms each at six application levels, showed that lettuce can be grown satisfactorily with a very low nitrate content when supplied with ammonium sulphate and a nitrification inhibitor. For plants growing on nitrate N, the optimum midrib sap nitrate concentration as maturity approached was about 1400 mg/1 NO₃-N. Large losses of mineral N were observed from the peat medium, even in the absence of plants. A relationship is presented which would enable a lettuce grower to estimate whole-shoot nitrate concentration from a quick test of midrib sapi.e. NO₃-N (mg/kg in fresh shoot) =0.14×NO₃-N (mg/l in sap). Tipburn was worst at intermediate levels of applied N, and was less serious with pure ammonium nutrition than with nitrate.     

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.     

水稻苗期磷高效基因型筛选研究

采用难溶性磷酸盐Ca3 (PO4) 2 为唯一磷源 ,在pH值为 5 .5条件下产生相对高浓度低磷胁迫及以NaH2 PO4为磷源配制P浓度为 0 .5mg·L-1的相对低浓度低磷胁迫的两个水培环境 ,分别对不同基因型水稻的磷效率进行评价 .以相对分蘖干重 (RTW )、相对总生物量 (RPW )、相对分蘖数 (RTN)、相对根系干重(RRW )、相对地上部干重 (RSW )、相对叶龄 (RLA)和相对株高 (RPH)作为耐性指标进行相关分析 .结果表明 ,供试材料的磷效率存在极显著差异 ,若以能产生分蘖的相对高浓度低磷胁迫进行筛选时 ,相对分蘖干重、相对地上部干重、相对总生物量可作为较好的筛选指标 ,其中相对分蘖干重不仅与其它指标间的相关性强 ,且品种间差异和变异系数均较大 ,能准确、灵敏地反映不同基因型间的耐低磷胁迫能力 ;若采用相对低浓度的低磷胁迫对不同基因型水稻进行耐低磷种质筛选时 ,筛选指标则不同 ,最好的单一筛选指标应是相对地上部干重或相对总生物量 .     

Nitrate accumulation in plants: a role for water

Plant nitrate and water contents (g^-1 dry weight) were monitored (1) in tomato plants in a growth room, during the day/night cycle with varied light intensities; (2) in two lettuce cultivars during the day/night cycle in a growth room and during growth in a glasshouse. Large, concurrent, and linearly correlated changes in nitrate and water contents were observed in both species and time-scales. Although these changes were dependent on light intensity and other environmental conditions, the slope of their relationship was not affected. Furthermore, when a limiting nitrate nutrition regime was applied to tomato, a significant and concurrent reduction of both plant nitrate and water contents was observed. Thus, when compared on the same water content basis, their nitrate content was only slightly reduced. These nitrate and water content changes were also observed in plant parts, and confirmed, through data extracted from the literature, in a large number of species (annuals and perennials) and other environments (open-field, soil culture). They are interpreted as an effect of homoeostasis for endogenous nitrate concentration (mol m^-3), and it is suggested that nitrate content changes (mol g^-1 dry wt.) result from the varying size of a water reservoir (m³ g^-1 dry wt.) whose nitrate concentration is regulated. From this viewpoint, the concept of critical nitrate concentration is discussed, and it is proposed to introduce explicitly water content in plant nitrogen models.Keywords: Nitrate content, water content, homoeostasis.      

Relationships between Nitrate Reductase Activity, Plant Weight and Nitrogen Content in Seedlings of Triticum, Aegilops and Triticale

Seedlings of 12 genotypes were grown in pots and watered withnutrient solutions providing 0, 1, 6 and 20 mg equivalents ofnitrate per I. Increasing the external nitrate supply broughtabout increases in plant weight, nitrate, reduced nitrogen concentrationsand in vivo nitrate reductase activity. When given solutioncontaining 6 mg equivalents of nitrate per litre, the plantscontained approximately 0.1 per cent nitrate, a concentrationsimilarto that found in field-grown plantsat thesamestage of growth.At the 6 mg equivalent level nitrate supply, nitrate reductaseactivity was strongly positively correlated with the concentrationsof nitrate and reduced nitrogen and negatively correlated withplant weight. Similar, though weaker, correlations were foundat the lower and higher levels of nitrate supply. The two Triticalegenotypes however, had higher than average plant weights andnitrate reductase activities, while plants of the two Aegilopsspecies weighed much less, especially at the higher levels ofnitrate supply, than the average of all 12 genotypes and generallyhad correspondingly greater nitrate and reduced nitrogen concentrationsand nitrate reductase activities. For individual genotypes,plant weight at a given level of nitrate supply was stronglycorrelated with weight at all other levels. In a second experiment seedlings of 150 genotypes were grownin compost watered with 10 mM Ca(NO₃)₂ Nitrate and reduced nitrogenconcentrations were negatively correlated with plant weightbut there was no significant correlation between nitrate reductaseactivityand either plant weight, nitrate or reduced nitrogen concentration. The results are taken to indicate that genetic factors, otherthan those determining the supply of reduced nitrogen, werelimiting growth and that as a consequence small plants accumulatednitrate and reduced nitrogen compounds in greater concentrationsthan large ones. The greater nitrate concentrations in smallplants may have induced the increased nitrate reductase activityfound in these, as compared with larger plants. Because plantweight varied more than did reduced nitrogen concentration,variation in reduced nitrogen per plant was more highly correlatedwith plant weight than with per cent reduced nitrogen.     

Role of phloem sap quality and exudation characteristics on performance of pea aphid grown on lucerne genotypes

The phloem sap of two lucerne (Medicago sativa L.) genotypes inducing differences in pea aphid,Acyrthosiphon pisum Harris (Homoptera: Aphididae) performances (weight, fecundity, survival), was collected by stylectomy (radio frequency microcautery). Sugars and amino acids were assayed. No significant difference in their concentrations could be established between genotypes. It is thus unlikely that a substantial part of the varietal resistance of these lucerne genotypes to pea aphid could be related to the content in sugars or amino acids. The same conclusion was drawn for the sugar/amino acid ratio. The amino acid profiles were globally similar. They nevertheless allowed a discrimination between the two genotypes on a few amino acids (alanine, leucine, isoleucine, arginine, ornithine) only. Moreover, the degree of resistance can be related neither to GABA concentration, nor to that of sulfur amino acids, because these constituants were either absent, or in trace amounts, whatever the lucerne genotype taken into account. Stylectomy parameters revealed some interesting differences in the sap exudation of the two genotypes. Average volume of exudation by stylet and average duration of exudation were respective 2.8 and 2.3 times higher in the susceptible genotype. These results suggest a reduced flow of phloem sap, after puncturing of the sieve-tubes by the aphid stylets on the resistant genotype; this could result in a greater difficulty in phloem sap ingestion by aphids settled on the resistant genotype and thus in suboptimal performances.     

Xylem exudate composition and root-to-shoot nickel translocation in Alyssum species

Aims

An improved understanding of the Ni root-to-shoot translocation mechanism in hyperaccumulators is necessary to increase Ni uptake efficiency for phytoextraction technologies. It has been presumed that an important aspect of Ni translocation and storage involves chelation with organic ligands. It has been reported that exposing several Ni hyperaccumulator species of Alyssum to Ni elicited a large increase in the histidine level of the xylem sap. In later studies it was shown that as time progressed the histidine:Ni ratio dropped considerably. Moreover, previous studies analyzed the relationship between Ni and ligands in plants that were exposed to Ni only for a few hours and therefore obtained results that are unlikely to represent field soils where plants are at steady-state Ni uptake. The aim of this study was to understand the quantitative relationship between Ni and organic ligands in the xylem sap of various Alyssum genotypes or species that reached steady-state Ni uptake after being exposed to Ni in either nutrient solution or serpentine soil for up to 6 weeks.

Methods

Total Ni concentration, 17 amino acids, 9 organic acids, and nicotianamine were measured in xylem sap of 100-day old plants of Alyssum.

Results

Results showed that the concentration of Ni in xylem sap of various Alyssum genotypes was 10–100 fold higher than the concentration of histidine, malate, citrate, and nicotianamine, which were the predominant Ni ligands measured in the sap.

Conclusion

When the physiology of the whole plant is taken into account, our results indicate that the concentration of organic chelators is too low to account for the complexation of all the Ni present in the xylem sap of Alyssum at steady-state Ni hyperaccumulation, and suggest that most of the Ni in xylem sap of this species is present as the hydrated cation.     

Trace gases generated in closed plant cultivation systems and their effects on plant growth.

Interactions between plants and trace gases, especially ethylene, were investigated from two different viewpoints; ethylene is toxic for plant growth, whereas the ethylene release rate of plants can be utilized as a plant growth indicator. When lettuce plants and shiitake mushroom mycelium were cultivated in closed chambers, ethylene concentration increased with time. Ethylene was released both from lettuce plant and from shiitake mushroom mycelium. Dioctyl phthalate (DOP) and Dibutyl phthalate (DBP) were detected, and these concentrations reached 3.7 ngL-1 for DOP and 2.4 ngL-1 for DBP 4 days after closing. Organic solvents such as xylene and toluene and organic siloxane were detected with GCMS. Visible injury was observed in lettuce plants cultivated in the chambers and it seemed to result from trace contaminants such as DOP, DBP, organic solvents, dimethylsiloxane polymer, and ethylene. In order to obtain basic data of ethylene evolution from plants, ethylene concentration in a closed chamber in which the plants were cultivated under a controlled environment (25 degrees C air temperature, 60-70% relative humidity, 250-300 micromoles m-2 s-1 photosynthetic photon flux density (PPFD)) was measured. Lettuce (Lactuca sativa L. cv. Okayama) released ethylene more than Brassica rapa var. pervidis, Brassica campestris var. communis, and Brassica campestris var. narinosa. Ethylene release rate of intact lettuce plant was highly correlated with plant growth parameters such as dry weight, leaf area and photosynthetic rate. Ethylene release rates of intact lettuce plant were affected by cultivation conditions such as ambient CO2 concentration, light intensity and light/dark period. Increase in ambient ethylene level influenced lettuce growth even at the concentration of 0.1 microliter L-1. The level of ethylene inhibited leaf expansion and slightly accelerated chlorophyll degradation. It did not affect photosynthesis and transpiration, and also little affected dry matter accumulation. Thus, ethylene release characteristics were clarified and an effect of ethylene on lettuce growth was revealed. These findings are useful for determination of a threshold level of ethylene and a capacity of ethylene removal system in CELSS. On the other hand, a possibility of plant growth diagnosis by measuring ethylene concentrations was evaluated. As a result, it became clear that the measurement of ethylene concentration in CELSS is one of the useful non-destructive measurement methods for plant growth diagnosis. Further research is needed to investigate the applicability of the method to environmental stresses other than Ni and Co in nutrient solution.     

Fitness-related traits of allozyme genotypes in Bromus hordeaceus L. (Poaceae) associated with field habitat and experimental flooding

Genetic variation at alcohol dehydrogenase and phosphoglucose isomerase loci in Bromus hordeaceus has in an earlier study been found to show substantial microgeographic spatial structuring. The present study reports differences in fitness related characters between the enzyme genotypes, both from a field study and a greenhouse experiment. The field study showed overall differences in seed set between allozyme genotypes and also that Pgi-1b genotypes differed in number of seeds set at different levels of herb cover in their habitat. In the greenhouse, dry, normal or flooded conditions were applied. Seeds from individuals with the Adh-1b-11 genotype matured faster in the dry and slower in the flooded treatments than did seeds from individuals with the Adh-1b-22 genotype. Individuals containing Pgi-1b-1f1f alleles and Adh-1b-11 alleles are more plastic than individuals with other allele combinations, meaning that allozyme variation could partly explain what could be seen as adaptive phenotypic plasticity. Mean seed weight was different between dry and flooding treatments for Pgi-1b genotypes. There were also direct effects of allozyme genotype on the probability of survival, total plant weight, weight of reproductive parts, seed weight, days to seed maturation and the percentage of reproductive parts out of the total plant weight.     

Xylem Sap from Actinidia chinensis: seasonal Changes in Composition

Seasonal variation was followed in the content of total a-aminoacids, arginine, calcium, total carbohydrate, ß-galactosidaseactivity, magnesium, nitrate, phosphatase activity, phosphateand sulphate in vacuum-extracted xylem sap from Actinidia chinensisvar. hispida, the Chinese gooseberry or kiwifruit. There wasa marked increase in the concentration of most sap componentsjust prior to leaf emergence followed by a rapid decrease afterthe leaves had expanded. Experiments with excised extensionshoots showed that much of this spring-time increase in concentrationsof sap components was due to mobilization of nutrients withinthe shoot itself. Sap from the trunk and the older brancheschanged less in composition than did sap from the younger partsof the plant. The amplitude and direction of trends in concentrationof sap from the different parts of the plant varied with nutrientand with time. Analysis of vacuum-extracted xylem sap collectedduring periods of rapid transpiration from early summer onwardsgives a reliable indication of the composition of the transpirationstream. Actinidia chinensis, Chinese gooseberry, kiwifruit, storage reserves, xylem sap, amino acids, arginine, calcium, carbohydrate, ßgalactosidase, magnesium, nitrate, phosphatase, phosphate, potassium, sulphate