In the past several decades, the world’s population has been increased year by year. And cereal production similarly increased from 1.2 billion tons in 1969 to 2.8 billion tons in 2014 (FAOSTAT 1. data). Environmental factors play an essential role in crop plants development, such as temperature, light, drought, soil quality, nutrition, nanoparticles and so on. Environmental pollution, especially in soil, caused the crops production reduced due to affect root activity and impeded substance transport activity.
Many nanoparticles contribute to their promising suitability for solar cells, drug delivery, temperature sensors, indoor illumination, and field emission displays. Once nanoparticle is taken in through root pathway, it resulted in beneficial or opposite effect in plant development. Until now, several nanoparticles have been reported on the interactions with the plants, including carbonaceous nanomaterials (fullerenes and nanotubes), metal oxides, zero-valent metals, nanopolymers, QDs and other NPs (Ni(OH)2 and NaYF4) [1,2,3,4,5,6,7,8]. Actually, nanoparticles are different with nutrition, which are assimilated by root as anion or cation type. Base on the nanoparticle physical characteristic of composition, size, concentration and coating of nanoparticle, it plays different roles. To some degree, high concentrations or low concentrations of nanoparticles have opposite functions in plant development, as inhibited or promoted plants, respectively. Nevertheless, magnetic Fe3O4 even at the concentration of 2 mM does not cause serious injury in pumpkin (Cucurbita maxima) . These positive effects of nanomaterials on plants were mainly reported for Au or Ag nanoparticles, Cu nanoparticles, Al related nanoparticles, TiO2 nanoparticles, CeO2 nanoparticles, SiO2 nanoparticles and carbonnanotubes [10,11,12,13,14,15].
Always, most of high concentrations of the nanoparticles caused phytotoxicity by toxic ions, cell or tissue damage, production of excess ROS, catalytic reactions [16,17,18,19,20]. To detect nanoparticles in the plant tissues, there are several different detection mechanisms of nanoparticles, such as fluorescence signaling, QDs, in situ analysis, nanoparticles color and so on . Until now, little is known how nanoparticle affects crop plant development at metabolism level.
Wheat (Triticum aestivum L.) is one of the most important crop plants in the world, which supports the 1/3 of the food for human. Previously, it was reported that TiO2 nanoparticles with diameters ranging from 14 nm to 655 nm, were accumulated in wheat root. And TiO2 nanoparticles did not affect wheat seed germination, biomass and transpiration . As the nanoparticles enter into plant cell, there are several different pathways for transport, such as: vascular system, membrane system, plasmodesmata system and so on. Base on the size of pathway in vascular, membrane, plasmodesmata or other system, we found nanoparticle size from 50 to 100 nm only depended on membrane. Previously, we used NaBiF4 and BiF3 for analysis the roles in rice root development [23, 24]. We found that NaBiF4 inhibited rice root elongation, but promoted more crown root formation. We analyzed several ROS signaling genes, which displayed transcript level of OsOVP1, OsNIP2:1, and OsMT2 was reduced, but expression of OsMT2b increased . Exogenous application of nanoparticle of BiF3for treatment, which did not reduce rice root elongation, but not mediate OsOVP1, OsNIP2:1, OsMT2, and OsMT2b transcript level changed . Because the composition of these two nanoparticles, only one element (sodium) shows difference, which might interrupt the native balance system, for example, homeostasis of sodium-potassium balance.
Plants generally maintain a stable K+/Na+ ratio and a negative electrical membrane potential difference across the plasma membrane under a normal physiological state. Na+ enters into the roots through different channels and transporters . However, if the balance was broken, plant may start ROS response reactions. In this study, we found that wheat root was much more sensitive to NaBiF4 nanoparticles than BiF3 nanoparticles in root development, which caused the balance of sodium potassium pump affected.