Modeling the difference among Cucurbita in uptake and translocation of p,p'-dichlorophenyl-1,1-dichloroethylene

Functional analysis of TiO2 nanoparticle toxicity in three plant species

Titanium dioxide nanoparticles (nano-TiO2) are manufactured and used worldwide in large quantities. However, phytotoxicity research on nano-TiO2 has yielded confusing results, ranging from strong toxicity to positive effects. Therefore, in this research, the effects of nano-TiO2 on the germination and root elongation of seed and seedlings were studied. Additionally, the uptake and physiological responses of mature plants were investigated. Physical chemistry data were analyzed to assess the availability of nano-TiO2. Finally, a hydroponic system designed to overcome nano-TiO2 precipitation was used to reproduce the environmental conditions of actual fields. Nano-TiO2 did not have any effect on seed germination or on most of the plant species tested. Nano-TiO2 had positive effects on root elongation in some species. No physiological differences in enzyme activities or chlorophyll content were detected, even though the plants absorbed nano-TiO2. Physical chemistry data showed that nano-TiO2 agglomerated rapidly and formed particles with much bigger hydrodynamic diameters, even in distilled water and especially in a hydroponic system. Furthermore, agglomerated nano-TiO2 formed precipitates; this would be more severe in an actual field. Consequently, nano-TiO2 would not be also readily available to plants and would not cause any significant effects on plants. Our results and other reports suggest that titanium itself is not phytotoxic, even though plants absorb titanium. In conclusion, nano-TiO2 is not toxic to the three plant species, in vitro or in situ.

Predicting the accumulation of organic contaminants from soil by plants

Analytic expressions for maximum chemical concentration attained in plants, and time this takes for uptake from surrounding soil were derived from a simple two-compartment soil/water-plant model. To illustrate, for the antibiotic norflxacin undergoing first order loss in the soil/water phase with a rate constant of 0.544 days⁻¹, maximum concentration in soybean P(MAX) is predicted to occur after 2.79 days exposure and be independent of initial soil/water concentration SW₀ of 52.5 mg kg⁻¹ dry weight. For soybean, the relationship between P(MAX) and SW₀ is P(MAX) = 0.047SW₀, resulting in predicted maximum levels of 2.20 mg kg⁻¹ dry weight. Modelled plant concentrations agreed well with experimental data (R² = 0.91).

Understanding the physiological and molecular mechanism of persistent organic pollutant uptake and detoxification in cucurbit species (zucchini and squash)

Cucurbita pepo ssp pepo (zucchini) roots phytoextract significant amounts of persistent organic pollutants (POPs) from soil, followed by effective translocation to aboveground tissues. The closely related C. pepo ssp ovifera (squash) does not have this ability. In a DDE-contaminated field soil, zucchini roots and stems contained 3.6 and 6.6-fold greater contaminant than did squash tissues, respectively, and zucchini phytoextracted 12-times more DDE from soil than squash. In batch hydroponics, squash was significantly more sensitive to DDE (2-20 mg/L) exposure; 4 mg/L DDE significantly reduced squash biomass (14%) whereas for zucchini, biomass reductions were observed at 20 mg/L (20%). PCR select Suppression Subtraction Hybridization was used to identify differentially expressed genes in DDE treated zucchini relative to DDE treated squash or non-treated zucchini. After differential screening to eliminate false positives, unique cDNA clones were sequenced. Out of 40 shoot cDNA sequences, 34 cDNAs have homology to parts of phloem filament protein 1 (PP1). Out of 6 cDNAs from the root tissue, two cDNAs are similar to cytochrome P450 like proteins, and one cDNA matches a putative senescence associated protein. From the DDE exposed zucchini seedlings cDNA library, out of 22 differentially expressed genes, 14 cDNAs were found to have homology with genes involved in abiotic stresses, signaling, lipid metabolism, and photosynthesis. A large number of cDNA sequences were found to encode novel unknown proteins that may be involved in uncharacterized pathways of DDE metabolism in plants. A semiquantitative RT-PCR analysis of isolated genes confirmed up-regulation in response to DDE exposure.

Dieldrin uptake and translocation in plants growing in hydroponic medium

It has been known that the Cucurbitaceae family takes up a large amount of persistent organic pollutants from soils and that the translocation of those compounds in cucurbits is higher than those in non-cucurbits. To understand the persistent organic pollutant uptake mechanisms of plant species, we compared the dieldrin absorption and transportation potentials of several plants in hydroponic medium. Sorghum (Sorghum vulgare Moench), sunflower (Helianthus annuus L.), soybean (Glycine max), komatsuna (Brassica rapa var. peruviridis), white-flowered gourd (Lagenaria siceraria var. hispida), cucumber (Cucumis sativus L.), and zucchini (Cucurbita pepo L.) were grown in a dieldrin-added hydroponic medium for 10 d, and then the amount of dieldrin in their shoots and roots was measured. All of the roots contained dieldrin, whereas only the cucurbits (white-flowered gourd, cucumber, and zucchini) contained considerable amounts of dieldrin in their shoots. The dieldrin uptake to the roots depended on the concentration of the n-hexane soluble components in the roots, regardless of whether the dieldrin in the roots was translocated to shoots or not. The dieldrin uptake from the solution to the roots was thought to be due to a passive response, such as adsorption on the roots. The translocation of dieldrin from the roots to the shoots was probably through the xylems. The amounts of dieldrin in the shoots per transpiration rates were higher for cucurbits than for non-cucurbits. It seems likely that cucurbits have uptake mechanisms for hydrophobic organic chemicals.