Analysis of the mycorrhizal potential in the rhizosphere of representative plant species from desertification-threatened Mediterranean shrublands

An evaluation of the mycorrhizal status of desertification-threatened ecosystems has been recommended as a first step in rehabilitation/restoration approaches based on revegetation strategies using arbuscular mycorrhizal (AM) technology. Representative desertified semiarid areas were selected from southeast Spain where the vegetation is dominated by grasses, with Stipa tenacissima usually present, and with some patches of the shrubs Pistacia lentiscus, Rhamnus lycioides, Olea europaea subsp. sylvestris and Retama sphaerocarpa. The objective of this study was to evaluate the mycorrhizal potential in these soils, the contribution of the different species established to the mycorrhizal potential of the soils and to assess the main mycorrhizal propagules involved. There were more AM fungal propagules in the rhizospheres of all the shrub species studied compared with adjacent fallow soils, suggesting that AM propagules can be considered as a functional component of the resource islands developing around plant roots. R. sphaerocarpa and O. europaea had a higher capacity to enhance the development of mycorrhizal propagules in their rhizospheres than R. lycioides and P. lentiscus. Correlation analyses showed that the number of spores of the most representative AM fungal species, i.e. Glomus constrictum, and the total length of extraradical AM mycelium are the propagule sources which were best correlated with the mycorrhizal potential in terms of the number of “infective” AM propagules in the rhizosphere of the target plant species. The contribution of AM symbiosis to the potentiality of S. tenacissima as nurse plant was site dependent. Diversity of AM fungi present in the test area is rather low, indicating the high degree of degradation of the ecosystem. At most, only four AM fungal spore morphoecotypes were consistently detected in the rhizosphere of the target plant species.     

Chemical and productive properties of two Sardinian milk thistle (Silybum marianum (L.) Gaertn.) populations as sources of nutrients and antioxidants

Silybum marianum (L.) Gaertn. (milk thistle), grown as a medicinal plant in several countries, is considered as a weed in pastures and cereal crops but also as an interesting plant for biomass production. As an additional contribution to the full exploitation of a such promising species, two Sardinian populations of S. marianum were investigated for chemical composition, bioactive compounds and antioxidant properties at vegetative and reproductive stages. Dry matter yield was affected by the phenogical stage and differed between populations, ranging from 148 to 246 g plant^?1. Chemical composition did not differ between populations. Antioxidant capacity detected by means of ABTS [(2,2′-azinobis (3-ethylbenzothiazoline-6-sulphonic acid) diammonium salt)] and by DPPH (1,1-diphenyl-2-picrylhydrazyl) methods ranged from 3.45 to 5.42 and 3.83 to 6.32 mmol/100 g dry weight of Trolox equivalent antioxidant capacity, respectively. Differences in antioxidant capacity and bioactive compound contents in the different plant organs were found and also a significant linear correlation between antioxidant capacity and total phenolics and flavonoids, at flowering compared to vegetative stage. Research highlights antioxidant capacity in different organs of milk thistle and encourages the exploitation of biomass also as functional food, source of natural antioxidants and as a complementary fodder.     

Genetic characterisation of olive trees from Madeira Archipelago using flow cytometry and microsatellite markers

In this study, native olive plants from Olea maderensis (≡ O. europaea ssp. cerasiformis) and O. cerasiformis (≡ O. europaea ssp. guanchica), wild olives (O. europaea ssp. europaea var. sylvestris) and cultivated olives (O. europaea ssp. europaea var. europaea) were analysed with respect to genome size and microsatellite markers. The mean nuclear DNA content of O. maderensis was estimated as 5.97 ± 0.191 pg/2C, while the remaining studied taxa presented mean genome sizes ranging from 2.99 to 3.18 pg/2C. These data and the obtained simple sequence repeats (SSR) profiles, i.e., with 2–4 alleles in O. maderensis and a maximum of two alleles in the other taxa, enabled the identification of a new ploidy level, tetraploidy, for a species belonging to the Olea genus. Cluster analysis of the microsatellite data revealed a clear separation of each species in different clusters and a high genetic dissimilarity could be observed among genotypes belonging to different species. This work contributed to a better characterization of olive species and the obtained data can be helpful to support taxonomic studies, and to develop germplasm preservation strategies in endangered populations of O. maderensis from Madeira Archipelago.     

Mineral Element and Total Phenolic Composition and Antioxidant Capacity of Seeds and Aerial Plant Parts of Perennial Legumes

ABSTRACT

Naturally derived bioactive compounds with antioxidant activity and mineral component have a positive effect on human health. Consequently, legumes, including perennial species, have been used as healthy food or medicinal plants. Red clover (Trifolium pratense) and lucerne (Medicago sativa) have been researched more thoroughly for food components and supplements than zigzag clover (T. medium), black medick (M. lupulina), liquorice milkvetch (Astragalus glycyphyllos), cicer milkvetch (A. cicer), and sainfoin (Onobrychis viciifolia). However, information is scarce about the distribution of mineral elements and phenolics in plants of these species as well as the antioxidant capacity of their extracts. In this study, we determined the mineral composition and total phenolic concentration in seeds and whole aerial plant parts and morphological fractions of these perennial legumes, as well as the antioxidant activity of extracts of the above-mentioned plant parts. The legume accessions chosen for this study were rich in potassium (K), calcium (Ca), magnesium (Mg), phosphorus (P), zinc (Zn), and iron (Fe), especially at branching growth stage, and thus could be used for mineral fortification of staple foods. Astragalus species, particularly seeds of A. glycyphyllos, were the richest source of Fe. Trifolium pratense, T. medium, O. viciifolia, and A. cicer were valuable source of total phenolics and antioxidants. The flower and leaf extracts of red clover exhibited very strong 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity. In general, the tested perennial legumes and their plant parts have rich mineral composition and bioactive properties, and they can be used as functional ingredients to accommodate the need for a particular mineral element or a bioactive property.     

Survival of inocula and native AM fungi species associated with shrubs in a degraded Mediterranean ecosystem

Reconstitution of the potential of soil mycorrhizal inoculum is a key step in revegetation programs for semiarid environments. We tested the effectiveness of inoculation with native arbuscular mycorrhizal (AM) fungi or with an allochthonous AM fungus, Glomus claroideum, with respect to the growth of four shrub species, the release of mycorrhizal propagules in soil, within and outside the canopy, and the improvement of soil structural stability. Two years after outplanting, the mixture of native endophytes was more effective than, for Olea europaea subsp. sylvestris, Retama sphaerocarpa and Rhamnus lycioides, or equally as effective as, for Pistacia lentiscus, the non-native AM fungus Glomus claroideum, with respect to increasing shoot biomass and foliar NPK contents. The increases in glomalin concentration and structural stability produced by inoculation treatments in the rhizosphere soil of the all shrub species, except R. lycioides, ranged from about 55 to 173% and 13 to 21%, respectively. The mixture of native AM fungi produced the highest levels of mycorrhizal propagules in soil from the center of the canopy of P. lentiscus and R. lycioides, while plants of O. europaea and R. sphaerocarpa inoculated with G. claroideum had more mycorrhizal propagules than did those inoculated with the mixture of native fungi. The number of mycorrhizal propagules in soil outside the canopy of the four shrub species was 5-35 times higher in inoculation treatments than in soil of the non-inoculated plants.     

Nutritional Status of Mediterranean Trees Growing in a Contaminated and Remediated Area

Soil contamination may contribute to forest decline, by altering nutrient cycling and acquisition by plants. This may hamper the establishment of a woody plant cover in contaminated areas, thus limiting the success of a restoration program. We studied the nutritional status of planted saplings of Holm oak (Quercus ilex subsp. ballota (Desf.) Samp.), white poplar (Populus alba L.), and wild olive tree (Olea europaea var. sylvestris Brot.) in the Guadiamar Green Corridor (SW Spain) and compared it with established adult trees. Soils in this area were affected by a mine-spill in 1998 and a subsequent restoration program. The spill resulted in soil acidification, due to pyrite oxidation, and deposited high concentrations of some trace elements. In some sites, we detected a phosphorus deficiency in the leaves of Q. ilex and O. europaea saplings, as indicated by a high N:P ratio (>16). For O. europaea, soil contamination explained 40% of the variability in leaf P and was negatively related to chlorophyll content. Soil pH was a significant factor predicting the variability of several nutrients, including Mg, P, and S. The uptake of Mg and S by P. alba was greater in acidic soils. The monitoring of soil pH is recommended since long-term effects of soil acidification may negatively affect the nutritional status of the trees.     

Native soil organic matter as a decisive factor to determine the arbuscular mycorrhizal fungal community structure in contaminated soils

The present study of arbuscular mycorrhizal (AM) fungi is focused on the identification of AM ecotypes associated with different plants species (Poa annua, Medicago polymorpha, and Malva sylvestris) growing in three contaminated soils with different organic matter, phosphorus, and trace element (TE; Cu, Cd, Mn, and Zn) contents. Soils were amended with biosolid and alperujo compost. Shifts in AM fungal community structure, diversity, richness, root colonization, and plant TE uptake were evaluated. Soil properties and plant species had a significant effect on AM fungal community composition as well as on root colonization. However, AM fungal diversity and richness were only affected by soil properties and especially by soil organic matter that was a major driver of AM fungal community. As soil quality increased, Glomeraceae decreased in favor of Claroideoglomeraceae in the community, AM fungal diversity and richness increased, and root colonization decreased. No effect due to amendment (exogenous organic matter) addition was found either in AM fungal parameters measured or TE plant uptake. Our results revealed that the role of TE contamination was secondary for the fungal community behavior, being the native organic matter content the most significant factor.     

Diversity of the European indigenous wild apple Malus sylvestris (L.) Mill. in the East Ore Mountains (Osterzgebirge), Germany: I. Morphological characterization

Malus sylvestris (L.) Mill. is the only indigenous wild apple species in Europe and recognized as rare and endangered species. An important prerequisite for the preservation of M. sylvestris is the identification of ‘true type’ M. sylvestris individuals because hybrids with cultivated apple could be also occurred. In this study variations among 625 putative M. sylvestris trees originated in the East Ore Mountains were evaluated with 20 selected morphological traits. The importance of these traits concerning the differentiation of ‘true type’ and hybrids of M. sylvestris were determined by statistical analysis. The results demonstrated a strong correlation of individual traits and those contributing mostly to variation of M. sylvestris were detected by the Principal Component Analysis. The relationship of 284 M. sylvestris, 18 M.?×?domestica, M. floribunda 821 and M. robusta 5 individuals were calculated based on the morphological data and presented in a dendrogram. The individuals grouped in two main clusters and 68 hybrids of M. sylvestris were identified. The main result of the morphological data of these hybrids indicates that the grouping is mainly based on the flower and leaf pubescence and less on the fruit size.     

Abundance of arbuscular mycorrhizal fungi in relation to soil salinity around Lake Urmia in northern Iran analyzed by use of lipid biomarkers and microscopy

Saline soils around Lake Urmia in northern Iran constitute a stressed environment for plants and microbial communities, including arbuscular mycorrhizal (AM) fungi. Soil and root samples were collected from fields cultivated with the glycophytes Allium cepa L. and Medicago sativa L., and sites dominated by the halophyte Salicornia europaea L. Soil and root samples were analyzed for the AM fungal signature neutral lipid fatty acid (NLFA) 16:1ω5. The roots were also examined microscopically for mycorrhizal colonization. Each plant species was sampled across a salt gradient. Microscopic examination showed no AM fungal structures in the roots of S. europaea. The highest root colonization was recorded for M. sativa. The highest NLFA 16:1ω5 values were found in soil around M. sativa roots and the lowest in soil around S. europaea roots. We found evidence for stimulation of vesicle formation at moderate salinity levels in M. sativa, which is an indication of increased carbon allocation to mycorrhiza. On the other hand, we found a negative correlation between salinity and arbuscule formation in A. cepa, which may indicate a less functional symbiosis in saline soils.     

Taking it to the next level: Trophic transfer of marker fatty acids from basal resource to predators

Fatty acid (FA) analysis is used increasingly to investigate the trophic structure of soil animal food webs as the technique allows separation of the role of detrital resources such as bacteria, fungi and plant material for consumer nutrition. The applicability of FAs as biomarkers for different diets has been verified for Collembola and Nematoda. However, for the analysis of whole food webs it is crucial to know whether marker FA are valid for different taxa and whether they are transferred along the food chain to higher trophic levels, i.e. predators. Top-predators are integrators of lower level energy fluxes in food webs; therefore analysis of their FAs may allow to identify trophic pathways and to separate bacterial vs. fungal based energy channels. Chilopoda and Arachnida are among the main predators in soil food webs. Our aim was to test the applicability of marker FAs for these two predator taxa and to verify the trophic transfer of marker FAs of different basal resources via first order consumers into predators, i.e. over three trophic levels. Therefore, we investigated the transfer of FAs from different basal resources [fungi (Chaetomium globosum), plant leaf litter (Tilia europaea), Gram-positive (Bacillus amyloliquefaciens) and Gram-negative bacteria (Stenotrophomonas maltophilia)] via Collembola (Heteromurus nitidus) as first order consumers into predators [Lithobius forficatus (Chilopoda) and Pardosa lugubris (Arachnida)]. Fatty acid profiles of predators of food chains with different basal resources differed significantly. Marker FAs of basal resources were clearly detectable in predators, suggesting that FA analysis allows to separate trophic channels of soil food webs. By reflecting basal resources, FAs of predators allow tracking energy/resource fluxes through the food web and thereby clarifying the relative importance of bacterial vs. fungal vs. plant resources for soil animal food webs.     

Establishment of shrub species in a degraded semiarid site after inoculation with native or allochthonous arbuscular mycorrhizal fungi

The re-establishment of native shrub species in the Mediterranean basin serves to restore the characteristic biodiversity and to prevent the processes of erosion and desertification in semiarid areas. A field experiment was carried out in an abandoned semiarid agricultural Mediterranean area to assess the effectiveness of mycorrhizal inoculation, with a mixture of native arbuscular mycorrhizal (AM) fungi or an allochthonous AM fungus (Glomus claroideum), on the establishment of Olea europaea subsp. sylvestris L., Pistacia lentiscus L., Retama sphaerocarpa (L.) Boissier and Rhamnus lycioides L. seedlings in this area. One year after planting, shoot biomass of inoculated O. europaea and P. lentiscus seedlings was greater, by about 630% and 300%, respectively, than that of non-inoculated plants. Shoot biomass of G. claroideum-colonised R. sphaerocarpa plants was significantly greater than that of seedlings inoculated with the mixed native AM fungi after 12 months. The increase of R. lycioides growth due to inoculation with native AM fungi was significantly greater than that of G. claroideum-colonised seedlings during the same growth period. Inoculation with a mix of native AM fungi was the most effective treatment for increasing shoot biomass and N, P and K contents in shoot tissues of R. lycioides seedlings. The mixture of native AM fungi was the most effective with respect to colonisation of the roots of O. europaea and R. lycioides, but the native AM fungi and G. claroideum achieved similar levels of colonisation in P. lentiscus and R. sphaerocarpa. The use of native mycorrhizal potential as a source of AM inoculum may be considered a preferential inoculation strategy to guarantee the successful re-establishment of native shrub species in a semiarid degraded soil.     

Assessment of VA mycorrhizal inoculum potential in relation to the establishment of cactus seedlings under mesquite nurse-trees in the Sonoran Desert

A commonly observed preferential association was quantified between mature native mesquite (Prosopis articulata) trees and the seedlings of six cactus species (Pachycereus pringlei, Opuntia cholla, Lophocereus schottii, Machaerocereus gummosus, Lemaireocereus thurberi, Mammilaria sp.) in a previously-disturbed area of the Sonoran Desert of Baja California, Mexico. We hypothesized that, in addition to more favorable edaphic factors, the inoculum potential of beneficial vesicular–arbuscular mycorrhizal (VAM) fungi was higher, and therefore, more favorable for cactus seedling establishment under the mesquite tree canopy (UC) compared to adjacent barren areas (BAs) away from the trees. In the greenhouse inoculum potential assays, VAM fungi were detected in onion (Allium cepa) trap plants from all soil samples regardless of collection site, but cardon cactus (P. pringlei) trap seedlings formed no VAM even after 6.5 months. Test soils were further used to preinoculate new onion seedlings transplanted into pots, to serve as nurse plants to inoculate adjacent cardon seedlings by vegetative transfer. After 15 months, cardon seedlings did develop slight VAM colonization, confined exclusively to the outermost cortical layers. Examination of test soils for spores or root fragments revealed very few to none, and spore production on onion trap plant roots was also sparse even though colonization was high. Analysis of UC and BA soils revealed that the water holding capacity, nutrient content, cation exchange capacity, total carbon, and total nitrogen contents of the UC soils were all higher than those of the BA soils. Since the VAM inoculum density in this study was not different between sites under and away from the mesquite tree canopy, we concluded that VAM inoculum density is not the primary factor for the establishment of cactus seedlings and that edaphic factors probably play a more important role. Our results suggest, however, that VAM inoculum potential in these hot desert soils, although relatively low, is probably maintained in the upper layers by means of hyphal fragments rather than spores.     

The Influence of Carbon Dioxide or Ozone Concentration on Growth and Assimilate Partitioning in Seedlings of Nine Conifers

Abstract

Seedlings of nine different conifers were exposed to 355 and 730 μmol mol-1 CO₂, or low (> 15 nmol mol^?1) and elevated 0₃ concentration (70 nmol mol^?1) for 81–116 days. The experiments were conducted in growth chambers placed in a greenhouse. Increased CO₂ concentration enhanced the mean relative growth rate (RGR) and total plant dry weight by 4 and 33% in Larix leptolepis, by 4 and 38% in Larix sibirica, by 7 and 47% in Picea glauca and by 3 and 16% in Picea sitchensis, respectively. The growth rates and dry weights of Pimis contorta, Pinus mugo and Pseudotsuga menziesii were not significantly affected. Carbon dioxide enrichment enhanced RGR of two provenances of Picea abies by 4 and 6%, respectively, while a third provenance was unaffected. In Pimis sylvestris, only the RGR of one of three provenances was stimulated by CO₂ enrichment (4%).

After two growth seasons CO₂ enrichment enhanced RGR and total plant dry weight by 11 and 35% in Picea abies and by 12 and 36% in Pinus sylvestris, respectively. Elevated CO₂ decreased the shoot:root ratio in Larix leptolepis, and decreased the needlerstem ratio in Picea glauca, but increased it in Pseudotsuga menziesii.

Elevated O₃ significantly decreased the plant dry weight in Picea sitchensis, Pseudotsuga menziesii and in one of three provenances of Pinus sylvestris, while the other species and provenances were unaffected. Increased O₃ concentration increased the shoot:root dry weight ratio in one of three Picea abies provenances, in all three Pinus sylvestris provenances and in Pinus contorta. The needle:stem ratio was enhanced by O₃ in seven of the nine species. The O₃ exposure caused chlorosis of needles in all species except Pseudotsuga menziesii.     

Antioxidant and choleretic properties of Raphanus sativus L. sprout (Kaiware Daikon) extract

Brassica vegetables and glucosinolates contained therein are supposed to reduce the risk of cancer and to possess health-promoting properties. The benefits of a Brassica-based diet may be particularly expressed by eating sprouts, in which the glucosinolate content is higher than in mature vegetables. With this in mind, a first objective of this study was to evaluate the antioxidant properties of radish (Raphanus sativus L.) sprouts (Kaiware Daikon) extract (KDE), in which the glucosinolate glucoraphasatin (GRH), showing some antioxidant activity, is present at 10.5% w/w. The contribution of GRH to KDE's antioxidant activity was considered in two chemical assays (Trolox equivalent antioxidant capacity and Briggs-Rauscher methods). The total phenol assay by Folin-Ciocalteu reagent was performed to quantify the reducing capacity of KDE. Finally, on the basis of the putative choleretic properties of antioxidant plant extracts, the effect on the bile flow of KDE administration was investigated in an animal experimental model. The findings showed that KDE has antioxidant properties and significantly induced bile flow in rats administered 1.5 g/kg of body weight for 4 consecutive days.     

Ash Leaching of Forest Species Treated with Phosphate Fire Retardants

The chemical, mineralogical, and leaching behavior of three dominant Greek forest species ashes (Pinus halepensis, Pistacia lentiscus, and Olea europaea), before and after treating forest species with diammonium phosphate (DAP) 5% and 10% weight to weight, have been studied using a new five-step shake leaching method at pH?=?6. For the analysis of ashes (prior and after leaching) and leachants, the following analytical techniques were used: atomic absorption spectroscopy, X-ray diffraction, and scanning electron microscopy with energy dispersive X-ray fluorescence analysis. The presence of DAP obstructs the extraction process of some metal ions (i.e., Na, K) contained in ashes by converting the soluble carbonate salts to the less soluble phosphates (i.e., Na₂CO₃ → Na₃PO₄). On the contrary, DAP enhances the mobility of some other metals (i.e., Ca) by forming more soluble compounds [i.e., CaCO₃ → Ca₃(PO₄)₂]. In addition, the presence of DAP lowers the pH of leachates, causing dissolution of some toxic elements (i.e., Mn, Pb, Zn). Unexpectedly, DAP prevents the leachability of Cr from ash. The above study concerns the environmental effects (soil and ground and underground water streams) caused by the use of chemical retardants on forest fires.     

Differential reaction of Pinus sylvestris, quercus robur and Q. petraea trees to nitrogen and sulfur pollution

Establishment of the Nitrogen Fertilizer Factory in Pulawy, Poland (NFFP) in 1966 resulted in contamination of the environment with nitrogen and sulfur compounds. As a result, radial stem growth declined in Pinus sylvestris and increased in Quercus robur. In this study we explored possible causal agents responsible for differences in pollution response among P. sylvestris, Q. robur and Q. petraea species, including differential uptake of nitrogen oxide pollutants by foliage and nutrient imbalances. We compared trees growing in the vicinity of the NFFP and a control area and found that Q. robur leaves were characterized by a relatively smaller N increase than those of P. sylvestris. It is possible that relatively high accumulation of N by pine could cause metabolic dysfunction in that species. However, differences in the concentration of nitrogen or activity of nitrate reductase did not sufficiently explain observed growth differences among the studied species. It is likely that among the factors contributing to the increased growth of oaks after the establishment of NFFP there is the rapid decline and mortality of pollution-sensitive Scots pine trees, easing competition for light and nutrients in the remaining Quercus trees.     

Elemental composition of different plant species

Element concentrations in leaves and needles of different plant species (Rhizophora mangle, Aster tri‐polium, Vaccinium vitis—idaea and Pinus sylvestris) are presented in the form of element concentration cadasters with reference to their abundance. The concentration cadasters of the two halophytes (Rhizophora mangle and Aster tripolium) show that the elements Na, Cl, Br and Sr occur at high concentrations in halophytes. The changes in chemical abundances of halophytes can be attributed to the extreme habitat conditions, i. e. physiological drought, under which they grow. Certain elements are preferentially accumulated in specific plants, e. g. Mn in Vaccinium vitis‐idaea.     

Regeneration of mixed deciduous forest in a Dutch forest-heathland, following a reduction of ungulate densities

The conversion of single-species coniferous forest stands into mixed stands by promoting the natural regeneration of indigenous broadleaved tree species was studied in a forest-heathland on the Veluwe, in the central part of the Netherlands. Red deer (Cervus elaphus), roe deer (Capreolus capreolus) and wild boar (Sus scrofa) had a large impact on regeneration dynamics, as was established by comparing 20 pairs of fenced and unfenced plots (40 × 40 m) during a 10-year period. A fivefold reduction of total herbivore biomass to 500 kg per km², resulted in a strong increase of shrub and tree sapling numbers in all vegetation types. However, height growth of the most palatable broadleaved tree species was still strongly impeded. Under the present-day grazing pressure, Scots pine (Pinus sylvestris) and beech (Fagus sylvatica) will become the dominant canopy species in the forests in the near future. It is argued that the most browse-sensitive woody species such as pedunculate and sessile oak (Quercus robur and Q. petraea) will successfully regenerate, only if temporal and spatial variation in browsing pressure is allowed to occur.     

Correlation analyses of phytochemical composition, chemical, and cellular measures of antioxidant activity of broccoli (Brassica oleracea L. Var. italica)

Chemical measures of antioxidant activity within the plant, such as the oxygen radical absorbance capacity (ORAC) assay, have been reported for many plant-based foods. However, the extent to which chemical measures relate to cellular measures of oxidative stress is unclear. The natural variation in the phytochemical content of 22 broccoli genotypes was used to determine correlations among chemical composition (carotenoids, tocopherols and polyphenolics), chemical antioxidant activity (ORAC), and measures of cellular antioxidation [prevention of DNA oxidative damage and of oxidation of the biomarker dichlorofluorescein (DCFH) in HepG2 cells] using hydrophilic and lipophilic extracts of broccoli. For lipophilic extracts, ORAC (ORAC-L) correlated with inhibition of cellular oxidation of DCFH (DCFH-L, r = 0.596, p = 0.006). Also, DNA damage in the presence of the lipophilic extract was negatively correlated with both chemical and cellular measures of antioxidant activity as measured by ORAC-L (r = -0.705, p = 0.015) and DCFH-L (r = -0.671, p = 0.048), respectively. However, no correlations were observed for hydrophilic (-H) extracts, except between polyphenol content and ORAC (ORAC-H; r = 0.778, p < 0.001). Inhibition of cellular oxidation by hydrophilic extracts (DCFH-H) and ORAC-H were approximately 8- and 4-fold greater than DCFH-L and ORAC-L, respectively. Whether ORAC-H has more biological relevance than ORAC-L because of its magnitude or whether ORAC-L bears more biological relevance because it relates to cellular estimates of antioxidant activity remains to be determined. Chemical estimates of antioxidant capacity within the plant may not accurately reflect the complex nature of the full antioxidant activity of broccoli extracts within cells.     

Vitamin C equivalent antioxidant capacity (VCEAC) of phenolic phytochemicals

To express the antioxidant capacity of plant foods in a more familiar and easily understood manner (equivalent to vitamin C mg/100 g), two stable radical species, ABTS(*)(-) and DPPH(*), commonly used for antioxidant activity measurements, were employed independently to evaluate their efficacies using apple polyphenolic extracts and seven polyphenolic standards including synthetic Trolox. Their antioxidant activities were expressed as vitamin C equivalent antioxidant capacity (VCEAC) in mg/100 g apple or mg/100 mL of the reference chemical compounds in 10 and 30 min using the ABTS(*)(-) and DPPH(*) scavenging assays, respectively. The antioxidant capacity of Gala apples and seven phenolic standards, determined by both ABTS(*)(-) and DPPH(*) scavenging assays, showed a dose-response of the first-order. Fresh Gala apples had a VCEAC of 205.4 +/- 5.6 mg/100 g using the ABTS assay, and the relative VCEACs of phenolic standards were as follows: gallic acid > quercetin > epicatechin > catechin > vitamin C > rutin > chlorogenic acid > Trolox. With the DPPH radical assay, the VCEAC of fresh Gala apples was 136.0 +/- 6.6 mg/100 g, and the relative VCEACs of seven phenolic standards were, in decreasing order, as follows: gallic acid > quercetin > epicatechin > catechin > or = vitamin C > Trolox > rutin > chlorogenic acid. Because the ABTS assay can be used in both organic and aqueous solvent systems, employs a specific absorbance at a wavelength remote from the visible region, and requires a short reaction time, it is a more desirable method than the DPPH assay. Therefore, it is recommended that antioxidant capacity be expressed as vitamin C mg/100 g equivalent (VCEAC) using the ABTS assay.