Understanding plant interactions with nanoparticles is of increasing importance for assessing their toxicity and trophic transport. The primary objective of this study was to assess uptake, biodistribution and toxicity associated with exposure of tobacco plants (Nicotiana xanthi) to gold nanoparticles (AuNPs). We employed synchrotron-based X-ray microanalysis with X-ray absorption near-edge microspectroscopy and high resolution electron microscopy to localize AuNPs within plants. Results from these experiments reveal that AuNPs entered plants through the roots and moved into the vasculature. Aggregate bodies were also detected within root cell cytoplasm. Furthermore, AuNP uptake was size selective as 3.5 nm AuNP spheres were detected in plants but 18 nm AuNPs remained agglomerated on the root outer surfaces. Finally, leaf necrosis was observed after 14 days of exposure to 3.5 nm AuNPs. Overall, results of this work show the potential for AuNPs to enter plants through size-dependent mechanisms, translocate to cells and tissues and cause biotoxicity.

Shell@core-nanostructured TiO(2)@ZnO n-p-n heterojunction nanorods with diameter of 30 nm were successfully fabricated via a hydrothermal method. The photodegradation rate of the TiO(2)@ZnO n-p-n nanorods evaluated by photodegrading methyl orange has been demonstrated to increase three times compared to that of wurtzite hexagonal ZnO. Anatase TiO(2) and Ti(2)O(3) grow along ZnO crystal lattices, which forms p-type Zn(2+) doped Ti(2)O(3) in the interface of TiO(2)/ZnO and therefore numerous n-p-n heterojunctions owing to the substitution of Ti(3+) by Zn(2+). Under the drive of inner electric field, the photogenerated electrons are both injected to the conduction band of Zn(2+) doped Ti(2)O(3) from conduction bands of ZnO and TiO(2), which efficiently enhances the separation of photogenerated electron-hole pairs and accelerates the transport of charges. The results suggest that TiO(2)@ZnO n-p-n heterojunction nanorods are very promising for enhancing the photocatalytic activity of photocatalysts.

Despite a potentially key role in cell-to-cell communication, plant intercellular connections-the plasmodesmata-have long been a biological "black box." Little is known about their protein composition, regulatory mechanisms, or transport pathways. However, recent studies have shed some light on plasmodesmal function. These connections have been shown to actively traffic proteins and protein-nucleic acid complexes between plant cells. This review describes these transport processes-specifically, cell-to-cell movement of plant viruses as well as endogenous cellular proteins-and discusses their possible mechanism(s). For comparison and to provide a broader perspective on the plasmodesmal transport process, the current model for nuclear import, the only other known example of transport of large proteins and protein-nucleic acid complexes through a membrane pore, is summarized. Finally, the function of plasmodesmata as communication boundaries within plant tissue is discussed.

SummaryHeavy metals, such as cadmium, have a significant impact on plant physiology. However, their potential effect on plant-pathogen interaction, an important biological process, has not been examined. This study shows that exposure of tobacco plants to non-toxic concentrations of cadmium completely blocked viral disease caused by turnip vein clearing virus. Cadmium-mediated viral protection was due to inhibition of the systemic movement of the virus, i.e. its spread from the inoculated into uninoculated leaves. Exposure of plants to cadmium had no effect on viral replication, assembly and local movement within the inoculated leaf. Analysis of the viral presence in different tissues suggested that cadmium treatment inhibited virus exit from the vascular tissue into uninoculated leaves rather than its entry into the host plant vasculature. Higher, toxic levels of cadmium did not produce this inhibitory effect on viral movement, allowing the systemic spread of the virus and development of the viral disease. These observations suggest that cadmium-induced viral protection requires a relatively healthy, unpoisoned plant in which non-toxic levels of cadmium may trigger the production of cellular factors which interfere with the viral systemic movement.