Assessing phytotoxicity of microplastics on aquatic plants using fluorescent microplastics.

Although studies on microplastics are increasing every year, still very little is known about their toxicity. Especially for plant species, even studies of uptake of microplastics are only few, not to mention phytotoxicity of microplastics. Therefore, we conducted a pilot study on the phytotoxicity of 1-µm-sized fluorescent microplastics (FMPs) on the free-floating aquatic plants Spirodela polyrhiza and Salvinia natans and the emergent aquatic plant Phragmites australis using 0.1% and 0.01% FMP treatment. Furthermore, uptake of FMPs by plants was verified by detecting fluorescence of FMPs by laser. A free-floating aquatic plant S. polyrhiza and emergent aquatic plant P. australis showed significantly decreased harvested biomass after 3 weeks indicating phytotoxicity of FMPs, but S. natans did not show any differences of harvested biomass or chlorophyll contents among treatments. Detection of fluorescence from plant leaves provided evidence of active FMPs uptake by plants. The emission spectra of plant leaves in 0.1% FMP treatment showed similar peaks to those of free fluorescent microplastics, providing a firm evidence of FMPs uptake by plants. This study is one of the pioneering studies to explore fluorescent microplastic uptake and toxicity in aquatic plants and therefore provides a baseline for further studies.

Development of a preliminary environmental risk assessment system by using text mining for introducing alien crops.

Changes in worldwide crop trends and climate change has increased the introduction of alien crops. However, there are always potential side effect issues related to introduced crops, such as the introduced crop becoming a nuisance at the new country or bringing insect pests or microorganisms with the introduced crops. In this study, we developed a crop introduction risk assessment system using text mining method to prevent this problem. First, we designed the "Preliminary Environmental Impact Assessment Index for Alien Crops" based on ecological researches to assess the risks of introduced crops to the natural environment. The questionaries evaluate the target alien crop with previous cases reporting the target crops' adverse effects on the environment, the potential of target crops' direct or indirect damage on the environment. The index has sixteen questions with allocated scores that are divided into 4 categories. The detailed rationales of the questionaries and the assessment index are discussed in main text. Second, we assessed 67 crop species that were introduced or scheduled to be introduced to South Korea with this Preliminary Assessment Index. The literature and data were collected with JabRef, search engines, and from the documents of six international institutions. Finally, based on the preliminary assessment results of selected species, we developed the protocols and a manual for the preliminary environmental risk assessment of introduced species. Final evaluation scores for risk evaluation for introducing crops are suggested (over 70 total score for 'danger' and over 50 points for 'caution required', and under 50 points for 'low expected impact'). Presented crop introduction risk assessment system is effective to identify potential problem making crop species. The protocols and a manual that we provide in this study could be applied to other countries which have similar climate and environmental conditions, or after being adequately modified to their environmental factors such as climate, neighboring countries, major crops according to eating habits, and major vegetation.

Evidence that ERF transcriptional regulators serve as possible key molecules for natural variation in defense against herbivores in tall goldenrod.

We collected Solidago altissima clones to explore their leaf damage resistance, and as a result identified five accessions that exhibited variable defense abilities against the generalist herbivore Spodoptera litura. In order to characterize molecules involved in such natural variation, we focused on ethylene response factors (ERFs) that exhibited distinct transcription patterns in the leaves of the five accessions (e.g., S1 and S2) after wounding: the transcript of SaERF1 and SaERF2 was induced in wounded S1 and S2 leaves, respectively. Although transcription levels of SaERFs in leaves of the five accessions did not correlate with the accessions' phytohormone levels, these transcription levels accorded with the possibility that ethylene and jasmonate signaling play crucial roles in wound-induced transcription of SaERF1 in S1 leaves, and SaERF2 in S2 leaves, respectively. SaERF1 was found to be a positive regulator of the GCC box and DRE element in the upstream regions of promoters of defense genes, whereas SaERF2 served as a negative regulator of genes controlled through the GCC box. Transgenic Arabidopsis plants expressing SaERF1 or SaERF2 showed enhanced and suppressed transcript levels, respectively, of a defensin gene, indicating that ERFs may be partly responsible for herbivore resistance properties of S. altissima accessions.

Mint companion plants enhance the attraction of the generalist predator Nesidiocoris tenuis according to its experiences of conspecific mint volatiles.

Mint plants enable improvement of pest management by attracting herbivore enemies to constitutively released mint volatiles. The generalist predator Nesidiocoris tenuis is used worldwide to control agricultural pests, but little is known about whether mint can serve as a companion plant that attracts this predator. To examine this, olfactory responses of N. tenuis were assessed using apple mint, candy mint, and spearmint as odor sources. Of the volatiles released by these mint species, candy mint volatiles alone were more attractive than those from undamaged eggplant, and were as attractive as volatiles from eggplant damaged with Spodoptera litura larvae. However, no prominent preference for particular volatile(s) among the mint volatiles was shown by O. strigicollis. When N. tenuis had been previously exposed to candy mint, the predator showed a stronger preference for candy mint volatiles than damaged eggplant volatiles. It was, however, irrelevant whether the predator received benefit or not by predating animal prey during the mint-experience period. In contrast, spearmint-experience increased the preference for spearmint volatiles only when the predator acquired prey during the mint-experience period. These findings suggest that previous exposure of N. tenuis to some particular mint species can increase its preference for volatiles from the conspecific mints.

Mint companion plants attract the predatory mite Phytoseiulus persimilis.

Mint plants could theoretically serve as companion plants (CPs) that attract enemies of herbivores in tritrophic interactions. In order to explore the traits of mint volatiles as attractant cues for enemies of two-spotted spider mites, we performed Y-tube olfactometer assays of predatory mites, Phytoseiulus persimilis and Neoseiulus californicus, towards three mint species, apple mint, candy mint, and spearmint, as odor source. Clean candy mint and spearmint were attractive to P. persimilis, when compared with clean air and undamaged Phaseolus vulgaris plants serving as the target crop. Moreover, clean candy mint plants were even more attractive than volatiles from P. vulgaris plants damaged by spider mites. These predator responses were induced additively by candy mint volatiles plus volatiles from damaged P. vulgaris plants, as shown using both Y-tube olfactometer and open-space assay systems. However, the number of spider mite eggs consumed by P. persimilis on P. vulgaris plants did not differ in the presence compared to the absence of mint volatiles, indicating that mint volatiles affect the attraction but not the appetite of P. persimilis. Together, these findings suggest that the use of candy mint and spearmint as CPs is an ideal platform for spider mite pest management via the attraction of predatory mites.

Overexpression of geraniol synthase induces heat stress susceptibility in Nicotiana tabacum.

MAIN CONCLUSION: Transgenic tobacco plants overexpressing the monoterpene alcohol geraniol synthase exhibit hypersensitivity to thermal stress, possibly due to suppressed sugar metabolism and transcriptional regulation of genes involved in thermal stress tolerance. Monoterpene alcohols function in plant survival strategies, but they may cause self-toxicity to plants due to their hydrophobic and highly reactive properties. To explore the role of these compounds in plant stress responses, we assessed transgenic tobacco plants overexpressing the monoterpene alcohol geraniol synthase (GES plants). Growth, morphology and photosynthetic efficiency of GES plants were not significantly different from those of control plants (wild-type and GUS-transformed plants). While GES plants' direct defenses against herbivores or pathogens were similar to those of control plants, their indirect defense (i.e., attracting herbivore enemy Nesidiocoris tenuis) was stronger compared to that of control plants. However, GES plants were susceptible to cold stress and even more susceptible to extreme heat stress (50 °C), as shown by decreased levels of sugar metabolites, invertase activity and its products (Glc and Fru), and leaf starch granules. Moreover, GES plants showed decreased transcription levels of the WRKY33 transcription factor gene and an aquaporin gene (PIP2). The results of this study show that GES plants exhibit enhanced indirect defense ability against herbivores, but conversely, GES plants exhibit hypersensitivity to heat stress due to suppressed sugar metabolism and gene regulation for thermal stress tolerance.