The molecular mechanisms responsible for selenium (Se) tolerance and hyperaccumulation were studied in the Se hyperaccumulator Stanleya pinnata (Brassicaceae) by comparing it with the related secondary Se accumulator Stanleya albescens using a combination of physiological, structural, genomic, and biochemical approaches. S. pinnata accumulated 3.6-fold more Se and was tolerant to 20 mM selenate, while S. albescens suffered reduced growth, chlorosis and necrosis, impaired photosynthesis, and high levels of reactive oxygen species. Levels of ascorbic acid, glutathione, total sulfur, and nonprotein thiols were higher in S. pinnata, suggesting that Se tolerance may in part be due to increased antioxidants and up-regulated sulfur assimilation. S. pinnata had higher selenocysteine methyltransferase protein levels and, judged from liquid chromatography-mass spectrometry, mainly accumulated the free amino acid methylselenocysteine, while S. albescens accumulated mainly the free amino acid selenocystathionine. S. albescens leaf x-ray absorption near-edge structure scans mainly detected a carbon-Se-carbon compound (presumably selenocystathionine) in addition to some selenocysteine and selenate. Thus, S. albescens may accumulate more toxic forms of Se in its leaves than S. pinnata. The species also showed different leaf Se sequestration patterns: while S. albescens showed a diffuse pattern, S. pinnata sequestered Se in localized epidermal cell clusters along leaf margins and tips, concentrated inside of epidermal cells. Transcript analyses of S. pinnata showed a constitutively higher expression of genes involved in sulfur assimilation, antioxidant activities, defense, and response to (methyl)jasmonic acid, salicylic acid, or ethylene. The levels of some of these hormones were constitutively elevated in S. pinnata compared with S. albescens, and leaf Se accumulation was slightly enhanced in both species when these hormones were supplied. Thus, defense-related phytohormones may play an important signaling role in the Se hyperaccumulation of S. pinnata, perhaps by constitutively up-regulating sulfur/Se assimilation followed by methylation of selenocysteine and the targeted sequestration of methylselenocysteine.

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Using reclaimed water to irrigate food crops presents an exposure pathway for persistent organic contaminants such as perfluoroalkyl acids (PFAAs) to enter the human food chain. This greenhouse study used reclaimed water augmented with varying concentrations (0.2-40 μg/L) of PFAAs, including perfluorocarboxylates (C3F7COO(-) to C8F17COO(-)) and perfluorosulfonates (C4F9SO2O(-), C6F13SO2O(-), C8F17SO2O(-)), to investigate potential uptake and concentration-response trends in lettuce (Lactuca sativa) and strawberry (Fragaria ananassa). In addition, studies were conducted to evaluate the role of soil organic carbon concentrations on plant uptake of PFAAs. PFAA concentrations in lettuce leaves and strawberry fruit were measured for each aqueous PFAA concentration applied. PFAA plant concentrations increased linearly with the aqueous concentration for all PFAAs, with PFCAs bioaccumulating to a greater degree than PFSAs in the edible portions of the tested plants. Chain-length-dependency trends were evident in both lettuce shoot and strawberry fruit, with decreasing concentrations associated with increasing chain length. Perfluorobutanoate (PFBA) and perfluoropentanoate (PFPeA), both short-chain PFAAs (<8 carbon chain length), accumulated the most compared with other PFAAs tested in the edible parts of both lettuce and strawberry. PFAA concentrations in strawberry root and shoot were also measured at selected PFAA aqueous concentrations (0.4, 4, and 40 μg/L). Short-chain perfluorocarboxylates were the dominant fraction in the strawberry fruit and shoot compartments, whereas a more even distribution of all PFAAs appeared in the root compartment. Lettuce grown in soils with varying organic carbon contents (0.4%, 2%, 6%) was used to assess the impact of organic carbon sorption on PFAA bioaccumulation. The lettuce grown in soil with the 6% organic carbon content had the lowest bioaccumulation of PFAAs. Bioaccumulation factors for lettuce were correlated to carbon chain length of PFAAs, showing approximately a 0.4 to 0.6 log decrease per CF2 group. This study confirms that PFAAs can enter and bioaccumulate in food crops irrigated with reclaimed water. Bioaccumulation potential depends on analyte functional group and chain length, concentration in the reclaimed water, and organic carbon content of the soil.

Consumers have become increasingly aware of potential health benefits from diets rich in fruits and vegetables. While potato has not yet surfaced as a headline-grabber in this respect, there is increasing evidence that some genotypes may possess health attributes that warrant attention. Plant breeders rely on germplasm biodiversity to advance their programs and are also acutely aware of current marketing trends that relate to health attributes. Investigations of antioxidant properties for over 90 genotypes were conducted to characterize antioxidant profiles for the Colorado potato breeding program and to identify those especially rich in antioxidants. The objective was to summarize data based on total phenolics (TP), Trolox equivalent antioxidant capacity (TEAC) and vitamin C, as well as to provide LC/MS characterization of major phenolic compounds and glycoalkaloids for pigmented genotypes. Preliminary data from breast cancer cell culture inhibition studies were examined for relationships to in vitro chemical assays. Genotypes with red or purple skin and flesh consistently had the highest gallic acid equivalent TP, TEAC, and chlorogenic acid content. Baked tubers had lower TP levels, TEAC and vitamin C compared to uncooked, microwave cooked and boiled tubers. Environmental effects contributed year to year variation in TP and TEAC radical scavenging capacity. TP content increased after 6 to 7 months in refrigerated storage at 5±1°C in several highly pigmented, but not in white or yellow fleshed cultivars and selections. Major phenolic compounds, anthocyanins, and glycoalkaloid content were further investigated with LC/MS in six cultivars. The pigmented cultivars 'Purple Majesty' and 'Mountain Rose' contained considerably higher levels of chlorogenic acid isomers than the non-pigmented genotypes. In the nonpigmented genotypes, chlorogenic acid and glycolalkaloid content were highest in 'Rio Grande Russet'. Chlorogenic acid has been demonstrated to exhibit several desirable anticarcinogenic properties in recent biochemical investigations, as have several of the phenolic based anthocyanin pigments found in many colorful fruits and vegetables. Thus, comprehensive compositional profiles using LC/MS are of interest in characterizing germplasm for breeding purposes. Preliminary tests with phosphate buffered saline (PBS) extracts of baked tubers from six cultivars revealed that 'Rio Grande Russet' was most effective in inhibiting growth of breast cancer cultures MCF-7 and MDA-MB-468. 'Purple Majesty' inhibited to some extent, 'Mountain Rose' and 'Yukon Gold' had no inhibitory effect. A subsequent study with 21 genotypes where the initial extract was made with 80% acetone followed by drying and extraction in aqueous PBS differed from direct PBS extraction. Five genotypes including 'Russet Nugget' inhibited at 0.187% to 0.375% w/v of the cell culture Am. solution. However, IC 50 inhibition data was not strongly related to the in vitro chemical data for these cultivars.Resumen Los consumidores se han dado cuenta del potenc...