Uptake and Distribution of Nitrogen in Perennial Ryegrass: Effect of Additional Applications at Vegetative Growth

Abstract

Nitrogen (N) fertilization rate, form, and timing in perennial ryegrass (Lolium perenne L.) vary according to the purpose of the grass. Double or triple spring N applications are required in forage production of perennial ryegrass. Whereas in perennial ryegrass grown for seed production the effect of more than one application has not received much attention. The hypothesis is that in perennial ryegrass grown for seed production the utilization of applied N depends on the current N status. Perennial ryegrass was grown in a hydroponic system with two N rates: low‐N (0.2 mM) and high‐N (6.0 mM). After 47 days of growth, additional N was applied as double‐labeled ¹⁵NO₃ ^{? 15}NH₄ ⁺ on four successive occasions in order to distinguish between the recoveries of the initial N applications and the additional N applied. Growth parameters and N content were analyzed on five harvesting occasions. Additional N applications to plants with low N status were primarily used to increase both N content in all organs as well as shoot number. By contrast, in high‐N treatments, the additional N supplied was primarily used to increase total‐N content in leaves. In all treatments, leaves were the preferable storage organs for N, however, the results from the high‐N treatments suggest a shift to pseudo‐stems as the preferable storage organ when additional N was supplied. It is suggested that the current N concentration in perennial ryegrass determines the potential of the plants to utilize additional applied N.     

Interrelations in Phosphorus and Potassium Accumulation Characteristics of Plants Grown in Different Soil Types

Nutrient accumulation characteristics and mineral content of plants depend on several factors such as crop and site characteristics, environmental conditions, and soil nutrient levels. Nutrient interactions are rather complex and may have an important role in this context. It is evident that phosphorus (P)–potassium (K) interaction is a part of cation–anion balance in plants. Although several authors demostrated the positive P-K interaction in plants, results are still inadequate. Studies on P-K interaction and adequate P/K ratios are needed to improve nutrient efficiency. Pot experiments were carried out under greenhouse conditions with perennial ryegrass (Lolium perenne L.) grown in three soils different in texture, soil organic matter (OM), pH, and available nutrient levels: an Eutric cambisol, a Calcaric fluvisol, and a Haplic phaeosem. Soil samples were taken from selected plots of National Long-Term Fertilization Trials (NLFT) after 30 years of fertilization. Besides the unfertilized control, increasing rates of P were applied in four replicates at four levels of P supply resulting from long-term P fertilization. Dry-matter (DM) production, P and K accumulation characteristics, nutrient concentrations, and K/P ratios of perennial ryegrass were studied for 4 months by taking four cuts. From the results, it was evident that both P and K accumulation of plants were closely related to DM accumulation. Phosphorus accumulation characteristics and amounts of P taken up by plants responded both to the level of long-term P supply and to rates of freshly applied P. Better levels of P supply had a beneficial influence on K uptake and K concentrations in plants. Phosphorus concentrations ranged between 0.20% and 0.53% P, whereas concentrations of K were between 1.63% and 5.64%. As the interaction between P and K may influence that of other nutrients, further research is needed to identify these relationships.     

Mudflat soil amendment by sewage sludge: Soil physicochemical properties,perennial ryegrass growth,and metal uptake

Abstract

The fast pace of cropland loss in China is causing alarm over food security and China’s ability to remain self-reliant in crop production. Mudflats after organic amendment can be an important alternative cropland in China. Land application of sewage sludge has become a popular organic amendment to croplands in many countries. Nevertheless, the land application of sludge to mudflats has received little attention. Therefore, the objective of the present work was to investigate the impact of sewage sludge amendment (SSA) at 0, 30, 75, 150 and 300 t ha^?1 rates on soil physicochemical properties, perennial ryegrass (Lolium perenne L.) growth and heavy metal accumulation in mudflat soil. The results showed that the application of sewage sludge increased organic matter (OM) content by 3.5-fold while reducing salinity by 76.3% at the 300 t ha^?1 rate as compared to unamended soil. The SSA reduced pH, electric conductivity (EC) and bulk density in mudflat soil, increased porosity, cation exchange capacity (CEC) and contents of nitrogen (N), phosphorus (P), exchangeable potassium ions (K⁺), sodium ions (Na⁺), calcium ions (Ca²⁺) and magnesium ions (Mg²⁺) in comparison to unamended soil. There were 98.0, 146.6, 291.4 and 429.2% increases in fresh weight and 92.5, 132.4, 258.6 and 418.9% increases in dry weight of perennial ryegrass at 30, 75, 150, and 300 t ha^?1, respectively, relative to unamended soil. The SSA increased metal concentrations of aboveground and root parts of perennial ryegrass (p < 0.05). The metal concentrations in perennial ryegrass were Zn > Cr > Mn > Cu > Cd > Ni, and the metal concentrations in roots were significantly higher than aboveground parts. The metal accumulation in perennial ryegrass correlated positively with sludge application rates and available metal concentrations in mudflat soil. Land application of sewage sludge was proved to be an effective soil amendment that improved soil fertility and promoted perennial ryegrass growth in mudflat soil. However, heavy metal accumulation in plants may cause food safety concern.     

Effects of cadmium on growth parameters of endophyte‐infected endophyte‐free ryegrass

A greenhouse hydroponic experiment was conducted to study the effects of cadmium (Cd) on growth parameters of endophyte‐infected (EI) and endophyte‐free (EF) perennial ryegrass. The results showed that Cd stress (0.18 mM Cd) affected all measured plant parameters, regardless of whether they were endophyte‐infected or endophyte‐free. Endophyte infection enhanced tillering ability and reduced leaf elongation under conditions of Cd stress. Endophyte infection tended to reduce leaf and leaf‐sheath biomass of control plants (0 Cd), but tended to alleviate the detrimental effects of Cd regarding shoot biomass. As far as net–photosynthetic rate and maximal photochemical efficiency of photosystem II (Fv/Fm ratio) were concerned, no difference was observed between EI and EF leaves. Like other grasses, perennial ryegrass can accumulate Cd, and Cd concentrations in different organs were in the following order: root > sheath > leaf. Endophyte‐infected ryegrass accumulated more Cd than EF ryegrass, especially in the shoots.     

Thermal processing of vegetables increases cis isomers of lutein and zeaxanthin

Carotenoids, lutein and zeaxanthin, found in fruits and vegetables, comprise the macula pigment of the eye. These carotenoids exist in plants as the all-trans geometric form; however, in human plasma, cis isomers of these carotenoids have also been identified. Thermal processing can induce carotenoid trans to cis isomerization. The aim of this research was to determine if thermal processing induces isomerization of lutein and zeaxanthin and to quantify the extent of this reaction. High-performance liquid chromatography was used to separate and quantitate geometric isomers of lutein and zeaxanthin. Isomers were tentatively identified by UV-visible absorbance spectra, comparison of retention times to those of isomerized standards using C(30) chromatography, and mass spectrometry. Thermal processing increased the percent cis isomers of lutein and zeaxanthin up to 22 and 17%, respectively. Further studies are needed to consider the physiological impact of consuming carotenoid isomers in processed vegetables.     

Response of soil microbial communities to the herbicide mesotrione: A dose-effect microcosm approach

Mesotrione is a new selective herbicide used for maize crops. The responses of microbial communities of a chernozem soil (Limagne basin, France) to pure or formulated (Callisto^®) mesotrione, applied at three different doses [one fold field rate (1 × FR), 10 × FR and 100 × FR], were studied using a laboratory microcosm approach. The effects were assessed on the prokaryotic cell abundance, the overall microbial activities (substrate-induced respiration (SIR) and dehydrogenase activity (DHA)) and the genetic structure of the bacterial and fungal communities (temporal temperature/denaturing gradient gel electrophoresis (TT/DGGE)). Mesotrione dissipation was similar whatever the formulation applied and the amounts dissipated were positively correlated to application rates. Several biodegradation products including the metabolites 4-methylsulfonyl-2-nitrobenzoic acid (MNBA) and 2-amino-4-methylsulfonylbenzoic acid (AMBA) were detected from day 42 post-treatment, in 10 × FR and 100 × FR treated soils. No response of the soil microbial communities was detected in soil spread with both the 1 × FR applications. Overall soil microbial activity was stimulated from day 6 by 10 × FR of Callisto^® and more strongly by 100 × FR of pure mesotrione and Callisto^®, whereas prokaryote abundance did not increase before day 95 in both the 100 × FR treatments. Genetic structural shifts recorded from day 42 in the bacterial and fungal communities were small and mainly attributable to variations in band intensity. Maximum dissimilarity of the bacterial and fungal genetic structures between control and 100 × FR treated soils did not exceed 12% and 28%, respectively. The general pattern was that more consistent effects occurred with increasing exposure times, especially in both the 100 × FR treated soils. These microbial responses could be due to the stimulation of (i) adapted mesotrione-degrading microorganisms and (ii) the activity of resistant heterotrophic microbial groups promoted by dead biomass from sensitive organisms. In addition, at 100 × FR doses, pure mesotrione seemed to induce stronger microbial responses than Callisto^®, formulation which contains adjuvants with potential side-effects on some microbial populations. This experimental approach indicated that pure mesotrione and Callisto^® affected soil microbial communities, but the effects were only detected at doses far exceeding the recommended field rates.     

Determination of methyl isothiocyanate in air downwind of fields treated with metam-sodium by subsurface drip irrigation

Air concentrations of methyl isothiocyanate (MITC) were determined near two fields treated with metam-sodium (MS) by subsurface drip irrigation. The two study fields showed measurable airborne MITC residues during application of MS and for periods up to 48 h postapplication. Using a Gaussian plume dispersion model, flux values were estimated for all of the sampling periods. On the basis of the flux estimates, the amount of MITC that volatilized within the 48 h period was about 1.4% of the applied material. Compared to other studies, MITC residues in air measured during application by subsurface drip irrigation were up to four orders-of-magnitude lower than those previously published for applications involving delivery through surface irrigation water. Our measured concentrations of MITC in field air were at levels below current regulatory guidance and thresholds for adverse human health effects.     

Fixation and transfer of nitrogen by white clover to ryegrass

Abstract. ¹⁵N₂ was used in a sealed controlled environment chamber to investigate the transfer of fixed nitrogen from white clover to perennial ryegrass growing in soil in pots. There was no difference in the ¹⁵N content of roots and shoots of clover plants after exposure to ¹⁵N. No labelled fixed nitrogen was detected in ryegrass plants growing with the clover plants for a period of 129 days. There was therefore no evidence of rapid direct transfer (excretion) of fixed nitrogen from clover to ryegrass.     

Shikimate accumulates in both glyphosate-sensitive and glyphosate-resistant horseweed (Conyza canadensis L. Cronq.)

Horseweed (Conyza canadensis) is a cosmopolitan weed that commonly grows throughout North America. Horseweed that is not completely controlled by normal applications of glyphosate has been reported in western Tennessee. This research had three objectives: (1) to develop and validate an analytical procedure for the quantitative determination of shikimate, an important indicator of glyphosate activity in plants; (2) to confirm resistance to glyphosate in a horseweed population; and (3) to examine the accumulation of shikimate in both glyphosate-resistant and glyphosate-susceptible horseweed plants. The analytical procedure to determine shikimate used extraction with 1 M HCl for 24 h, followed by liquid chromatography using photodiode array detection, and shikimate recoveries were >or=82%. Glyphosate applications of both 0.84 kg ae/ha (the standard application rate) and 3.8 kg ae/ha to susceptible plants caused complete plant death. The same glyphosate applications to putative resistant populations caused less than 15% growth reduction as determined by visual evaluations, and fresh weights of these resistant plants 17 days after glyphosate treatment (DAT) were reduced an average of 45% in one population and were not affected in a different population. This direct comparison conclusively confirms that horseweed plants collected in western Tennessee in 2002 are resistant to 4 times the normal application dosage of glyphosate. The glyphosate-resistant horseweed biotypes still exhibited some herbicidal effects from the glyphosate, such as yellowing in the most actively growing, apical shoot meristems. The yellowing in the shoot apexes was transitory, and the plants recovered from this damage. Shikimate concentrations in all untreated horseweed plants were less than 100 microg/g, which was significantly less than that in all plants which had been treated with 0.84 kg ae/ha of glyphosate. Unexpectedly, shikimate accumulated (>1000 microg/g) in both resistant populations and the susceptible population. However, there were differences in shikimate accumulation patterns between resistant and susceptible horseweed biotypes. Shikimate concentrations in resistant populations declined about 40% from 2 to 4 DAT, while shikimate concentrations in the susceptible horseweed plants increased about 35% from 2 to 4 DAT. The confirmed resistance of a widespread weed implies that alternative control strategies for glyphosate-resistant horseweed will be needed in those no-tillage production systems where it commonly occurs.     

Host-fungus competition for carbon as a cause of growth depressions in vesicular-arbuscular mycorrhizal ryegrass

The effect of Gigaspora margarita an endomycorrhiza—forming fungus, on the growth and chemical composition of perennial ryegrass plants grown at three concentrations and two sources of N were studied. The yield of plant tops was significantly depressed by mycorrhizal infection. Mycorrhizal plants had higher concentrations of free NH₄⁺ (and, consequently, higher cation excess concentrations), suggesting an impairment of protein synthesis possibly resulting from an inhibited supply of C. Total oxidizable C, soluble sugar content and C/N ratios were lower in mycorrhizal plants, suggesting that the mycorrhizal fungi were competing with the host for photosynthetically-derived C, consequently causing growth depressions. A possible mechanism of this competition is discussed.     

The effect of age and cold hardening on resistance to pink snow mould (Microdochium nivale) in perennial ryegrass (Lolium perenne L)

Abstract

The effect of plant age and cold hardening on resistance to pink snow mould caused by Microdochium nivale was studied in perennial ryegrass. Resistance to M. nivale was estimated as relative regrowth after inoculation and incubation under artificial snow cover at 2°C. Resistance increased with increasing plant age. Cold hardened and unhardened plants of the same age displayed identical resistance. Preliminary studies indicate that expression of genes coding for the PR proteins chitinase and PR-1a increased during incubation of inoculated perennial ryegrass, but no clear difference in expression of these genes was found between plants of different ages, or in hardened versus unhardened plants.     

Residue levels of chlorpropham in individual tubers and composite samples of postharvest-treated potatoes

Chlorpropham, a herbicide and sprout suppressant, is used on stored potatoes to prolong the storage period without deterioration of produce quality. Data for residue concentrations on an individual tuber basis are required by WHO for the estimation of the variability factor. In this study, the levels of chlorpropham in individual tubers and in composite samples were determined. The distribution of chlorpropham between the peel and the tuber flesh was examined, and the fate during the cooking process (washing, boiling, frying) was studied. The concentrations in individual tubers ranged from 1.8 to 7.6 mg/kg 10 days postapplication (mean 3.8 mg/kg, RSD 39%), from 0.7 to 4.0 mg/kg 28 days postapplication (mean 2.9 mg/kg, RSD 28%), and from 0.8 to 3.8 mg/kg 65 days postapplication (mean 2.2 mg/kg, RSD 48%). The calculated residues in composite samples 10 days postapplication ranged from 4.3 to 6.1 mg/kg (mean 4.9 mg/kg, RSD 20%). Those in samples taken 28 days postapplication ranged from 3.1 to 4.2 mg/kg (mean 3.8 mg/kg, RSD 15%). The concentrations determined in composite samples of whole tubers 65 days postapplication ranged between 2.6 and 3.2 (mean 2.9 mg/kg, RSD 11%). Peeling removed 91-98% of the total residue; washing reduced residues by 33-47%. Detectable residues were found in boiled potatoes and the boiling water, and in french fries and the frying oil. Monitoring data on commercial prefried frozen french fries are reported.     

Influence of nitrogen and sulfur on biomass production and carotenoid and glucosinolate concentrations in watercress (Nasturtium officinale R. Br.)

Watercress (Nasturtium officinale R. Br.) is a perennial herb rich in the secondary metabolites of glucosinolates and carotenoids. 2-phenethyl isothiocyanate, the predominate isothiocyanate hydrolysis product in watercress, can reduce carcinogen activation through inhibition of phase I enzymes and induction of phase II enzymes. Sulfur (S) and nitrogen (N) have been shown to influence concentrations of both glucosinolates and carotenoids in a variety of vegetable crops. Our research objectives were to determine how several levels of N and S fertility interact to affect watercress plant tissue biomass production, tissue C/N ratios, concentrations of plant pigments, and glucosinolate concentrations. Watercress was grown using nutrient solution culture under a three by three factorial arrangement, with three S (8, 16, and 32 mg/L) and three N (6, 56, and 106 mg/L) fertility concentrations. Watercress shoot tissue biomass, tissue %N, and tissue C/N ratios were influenced by N but were unaffected by changes in S concentrations or by the interaction of NxS. Tissue pigment concentrations of beta-carotene, lutein, 5,6-epoxylutein, neoxanthin, zeaxanthin, and the chlorophyll pigments responded to changes in N treatment concentrations but were unaffected by S concentrations or through N x S interactions. Watercress tissue concentrations of aromatic, indole, and total glucosinolate concentrations responded to changes in N treatments; whereas aliphatic, aromatic, and total glucosinolates responded to changes in S treatment concentrations. Individual glucosinolates of glucobrassicin, 4-methoxyglucobrassicin, and gluconasturriin responded to N fertility treatments, while gluconapin, glucobrassicin, and gluconasturiin responded to changes in S fertility concentrations. Increases in carotenoid and glucosinolate concentrations through fertility management would be expected to influence the nutritional value of watercress in human diets.     

Phytochemical profiles and antioxidant activity of wheat varieties

Whole grain consumption has been associated with reduced risk of chronic diseases, such as cardiovascular diseases and cancer. These beneficial effects have been attributed to the unique phytochemicals of grains that complement those found in fruits and vegetables. Wheat is one of the major grains in the human diet; however, little is known about the inherent varietal differences in phytochemical profiles, total phenolic and carotenoid contents, or total antioxidant activities of different wheat varieties, which ultimately influence the associated nutritional and health benefits of wheat and wheat products. The objectives of this study were to determine the phytochemical profiles and total antioxidant activity for 11 diverse wheat varieties and experimental lines. The profiles included free, soluble-conjugated, and insoluble-bound forms of total phenolics, flavonoids, and ferulic acids and carotenoid content including lutein, zeaxanthin, and beta-cryptoxanthin. The results showed that total phenolic content (709.8-860.0 micromol of gallic acid equiv/100 g of wheat), total antioxidant activity (37.6-46.4 micromol of vitamin C/g), and total flavonoid content (105.8-141.8 micromol of catechin equiv/100 g of wheat) did not vary greatly among the 11 wheat lines. However, significant differences in total ferulic acid content (p < 0.05) and carotenoid content (p < 0.05) among the varieties were observed, with carotenoid content exhibiting the greatest range of values. Carotenoid content among the 11 wheat varieties exhibited 5-fold, 3-fold, and 12-fold differences in lutein, zeaxanthin, and beta-cryptoxanthin, respectively. A synthetic wheat experimental line, W7985, gave the lowest carotenoid concentrations of any of the genotypes in this study. Such large genotypic differences in carotenoid content may open up new opportunities for breeding wheat varieties with higher nutritional value.     

Effect of elevated manganese on the ultraviolet‐ and blue light‐absorbing compounds of cucumber cotyledon and leaf tissues

The effect of manganese [Mn(II)] on the pigments of cucumber (Cucumis sativus L., cv Poinsett 76) leaf and cotyledon tissues was investigated. Tissue disks (7 mm) were exposed to increasing Mn(II) concentrations from 100 μM to 2.5 mM. Acetone (carotenoid‐rich fraction) and acidified methanol (flavonoid‐rich fraction) extracts were analyzed by high performance liquid chromatography. Although none of the Mn(II)‐treated tissues showed visible damage, Mn(II) at concentrations of 250 μM and above significantly reduced (60%) the ß‐carotene levels of light‐incubated leaf tissues. A major Mn(II)‐induced, UV‐absorbing compound was observed in methanol extracts of cotyledonary tissues exposed to Mn(II) in the dark. In leaf tissues, Mn(II) reduced the levels of certain UV‐absorbing compounds under both light conditions. These results demonstrate that excess leaf Mn(II) can rapidly impair isoprenoid metabolism, altering tissue carotenoid composition. Furthermore, Mn(II) may also modify phenylpropanoid metabolism, changing the tissue flavonoid composition. Both situations could sensitize plant tissues to oxidative stresses, particularly enhanced solar UV‐B radiation, and may reduce the nutritional quality of leafy vegetables.     

Carotenoid Composition and Changes in Sweet and Field Corn (Zea mays) During Kernel Development

Kernels of two carotenoid‐rich cultivars, sweet corn Jingtian 5 and field corn Suyu 29, were compared in terms of carotenoid composition during corn kernel development. The results showed that eight principal carotenoids were characterized by HPLC with diode array detection and atmospheric pressure chemical ionization tandem mass spectrometry with a C30 column. During kernel development, there was a similar trend in the change of total carotenoids for both corn cultivars, and the variation of individual carotenoids was also somewhat similar; violaxanthin, zeaxanthin, lutein, α‐cryptoxanthin, and β‐cryptoxanthin contents had upward trends, whereas neoxanthin content declined all the time, and α‐carotene and β‐carotene had no significant changes. However, the highest levels of the major carotenoids lutein (41.61 µg/g, dry weight) and zeaxanthin (39.59 µg/g, dry weight) obtained in field corn Suyu 29 during the milk stage were higher than those in sweet corn Jingtian 5, whereas the other individual carotenoid levels were significantly lower. Compared with the grain color, highly significant positive correlations were observed between zeaxanthin, lutein, and violaxanthin contents and deeper yellow/orange coloration indicators for field corn Suyu 29, but these relationships were weak for sweet corn Jingtian 5. Potential genetic variation might exist for carotenoid accumulation in sweet and field corn kernels.     

太阳辐射减弱对冬小麦叶片光合作用膜脂过氧化及同化物累积的影响

为了探究气溶胶的太阳辐射减弱效应对农作物叶片生理特性及同化物累积的影响,以扬麦13为供试材料,在大田试验条件下系统研究了不同辐射减弱处理（100%、60%、40%、20%、15%）对冬小麦叶片光合作用、膜脂过氧化水平和同化物积累的影响。结果表明：太阳辐射减弱至自然光的60%-15%时,冬小麦叶片净光合速率减少15.8%-70.1%,光合色素的含量（叶绿素a、b和类胡萝卜素）显著提高,其中叶绿素b含量的增加最明显。太阳辐射减弱会抑制冬小麦叶片膜脂过氧化程度,减少细胞膜透性,且辐射减弱的程度越高,影响越大。当太阳辐射为自然光的60%-15%时,冬小麦叶片的可溶性糖含量比对照降低了32.22%-76.45%,可溶性蛋白含量降低了19.02%-48.12%,但总游离氨基酸含量比对照增加了47.46%-177.87%。上述结果表明,太阳辐射减弱后会减弱冬小麦光合作用,增加光合色素含量,抑制膜脂过氧化程度,从而导致作物体内同化物的累积受阻,糖类及蛋白质的含量显著降低,必然会影响作物的产量及品质形成。     

Remediation of a Sandy Soil Contaminated with Cadmium,Nickel, and Zinc using an Insoluble Polyacrylate Polymer

Abstract

This study was carried out to investigate whether an insoluble polyacrylate polymer could be used to remediate a sandy soil contaminated with cadmium (Cd) (30 and 60 mg Cd kg^?1 of soil), nickel (Ni) (50 and 100 mg Ni kg^?1 of soil), zinc (Zn) (250 and 400 mg Zn kg^?1 of soil), or the three elements together (30 mg Cd, 50 mg Ni, and 250 mg Zn kg^?1 of soil). Growth of perennial ryegrass was stimulated in the polymer‐amended soil contaminated with the greatest amounts of Ni or Zn, and when the three metals were present, compared with the unamended soil with the same levels of contamination. Shoots of plants cultivated in the amended soil had concentrations of the metals that were 24–67% of those in plants from the unamended contaminated soil. After ryegrass had been growing for 87 days, the amounts of water‐extractable metals present in the amended soil varied from 8 to 53% of those in the unamended soil. The results are consistent with soil remediation being achieved through removal of the metals from soil solution.     

Could iron nutrition status be evaluated through photosynthetic pigment changes?

Iron deficiency decreases the amount of photosynthetic pigments in higher plants, and also results in characteristic changes in the relative photosynthetic pigment composition. Iron deficient plants exhibit a relative increase in xanthophylls, largely attributable to pigments within the xanthophyll cycle, violaxanthin, antheraxanthin, and zeaxanthin. Furthermore, the xanthophyll cycle functions in Fe‐deficient plants, but not in other yellow, carotenoid enriched‐materials, such as etiolated or senescing leaves. When Fe‐deficient leaves are illuminated, part of the violaxanthin is converted into antheraxanthin and zeaxanthin. When Fe‐deficient leaves are placed in the dark, the cycle reverts back to violaxanthin. In this paper we present further data on this cycle and discuss the possible relevance of pigment changes as an alternative mechanism for the dissipation of excess energy. The possibility of using characteristic pigment changes as a tool for monitoring Fe status in higher plants is discussed.     

Trolox equivalent antioxidant capacity of different geometrical isomers of alpha-carotene, beta-carotene, lycopene, and zeaxanthin.

Isomerization of carotenoids, which is often encountered in food processing under the influence of temperature and light, may play a role in the observed protective effects of this group of secondary plant products. Investigation of in vitro antioxidant activity of prominent carotenoid geometrical isomers was undertaken in light of recent reports illustrating a large percentage of carotenoid (Z)-isomers in biological fluids and tissues. Alpha-carotene, beta-carotene, lycopene, and zeaxanthin were isolated from foods or supplements and subsequently photoisomerized with iodine as a catalyst. Major Z-isomers of each carotenoid were fractionated by semipreparative C(30) HPLC. In vitro antioxidant activity of all isomers collected was measured photometrically using the Trolox equivalent antioxidant capacity (TEAC) assay. TEAC values of 17 geometrical isomers investigated ranged from 0.5 to 3.1 mmol/L. Three unidentified (Z)-isomers of lycopene showed the highest antioxidant activity, being significantly higher than the result for (all-E)-lycopene, which had approximately two times the activity of (all-E)-beta-carotene. On the other hand, (9Z)-zeaxanthin had a more than 80% lower TEAC value compared to that of (all-E)-lycopene. These results allow for the in vivo relevance of (Z)-isomers of carotenoids to be considered.