The development of novel biopolymers based on chemical modification of naturally occurring polymers can be a highly cost-effective alternative with diverse opportunities for engineering novel delivery systems. Lignin is a byproduct of the pulping industry; 50–60 million tons of lignin are produced every year . Given its origin and properties, LN can be sustainably used for agricultural purposes given that its degradation products are humic acids that will enhance soil fertility. Lignin is a highly complex and heterogeneous polyphenolic polyether with a wide range of molecular weights. The complexity and abundance of the functional hydroxyl groups of lignin provides significant potential for chemical modification. For example, we previously successfully grafted LN with poly acid to form a novel LN-g-PLGA amphiphilic polymer which was further assembled into core-shell nanoparticles. The hypothesis of this study was that LN-g-PLGA nanoparticles would facilitate targeting and controlled release of a nonsystemic agrochemical. Methoxyfenozide , a commonly used non-systemic pesticide, was used as a model to determine release and translocation from soybean roots to shoots. MFZ is a diacylhydrazines insecticide used for the control of lepidopteran larvae; the pesticide is most effective when ingested by the larvae. MFZ has a low solubility in water and given its non-systemic nature, quantifying its presence in plants would be an ideal indicator for the effectiveness of this platform. To test this hypothesis, 28 days old soybean plants were treated with MFZ-loaded LNPs at three concentrations in a hydroponic system. After 6, 12, and 24 h, treated plants were harvested and MFZ content in the roots, stems and leaves was determined by liquid chromatography-mass spectrometry.

If the hypothesis is proven correct, this will allow for creating a bio-inspired platform to enable targeted and precise in planta delivery of non-systemic analytes. The development of a bio-inspired platform to enhance the efficient of non-systemic pesticides can be a novel and powerful approach in sustainable nano-enabled agriculture. The plants were exposed to free MFZ at three concentrations 0.27, 2.7, and 27.03 μg/ml for the low, fodder system for sale medium and high doses; and to the equivalent concentration of nanodeliverd MFZ, corresponding to 0.01, 0.1, and 1 mg/ml LNPs. Statistical analysis demonstrated that the time and the LNPs had a significant influence on the translocation of MFZ in all tissues .The concentration of MFZ in the roots increased over time when applied with a nanodelivery system, whereas the MFZ concentration in tissues of plants treated with free MFZ was consistent over the three time points tested. Similarly, MFZ concentration in the stems was higher for nanodelivered MFZ, especially at the longer times, 12 and 24 h, in the low and medium concentrations . The effect of time was most significant in the leaves, however.This is to be expected given that it will take time for the LNPs entering the roots to translocate the agrochemical, either still associated with the LNP or as free released analyte, from the roots to the leaves.

The MFZ concentrations in the leaves at the low, medium, and high LNP exposures increased over time; they measured 0.05, 0.15, and 0.22 μg/g at 6 h; 0.06, 0.48, and 0.44 μg/g at 12 h, and 0.08, 0.96, and 1.72 μg/g at 24 h of exposure and they were in most cases significantly different from the controls . To assess the ability of the LNPs to shuttle MFZ from the roots to the leaves, translocation efficiency was calculated as the percentage of MFZ translocated to the plant upper section as a function of the total amount taken up by a plant. TE has been used by others to demonstrate the efficiency of a delivery system to translocate a molecule from the roots to the shoots of plants. The TE achieved with LNPs was 0.065 at 24 h at a concentration of 0.01 mg/ml LNPs while at the higher concentration tested the TE decreased to 0.006 after 24 h, which is similar to results obtained by others.The decrease in the TE with increasing LNPs concentration can be attributed to the higher accumulation of MFZ in the root tissue at these high concentrations. The same reasoning explains the higher TE of the controls relative to the treatment. Even though the TE was higher for the controls, the total amounts translocated were significantly lower than the treatment and did not change significantly over time . The total amount of nanodelivered MFZ to roots, stems and leaves indicated that LNPs delivered ~7-fold more MFZ than the free form, and as high as ~17-fold with the low LNP concentration treatment after 24 h . Even though the size of the LNPs suggested lower to no translocation to the upper section of the plant, LNPs still showed a noticeable TE compared to other delivery systems with similar sizes. This can be attributed to the highly negative charge of the particles , which may have facilitated the translocation of the LNPs within the vascular system.

The specific mechanisms for NP translocation in plants are still not well understood and different species of plants posses distinct interactions with NPs as NPs must traverse different plant systems in order to be translocated to the leaves and shoots of the plant. There are two well known pathways for the internalization of analytes from the root epidermis to the xylem located in the endodermis; nanoparticle properties will determine which of these uptake pathways is followed. Apoplastic transport makes use of the capillary network located in the epidermis and cortex and requires osmotic pressure and a concentration gradient to transport certain minerals, whereas other compounds are more selectively accumulated. This mechanism is known as passive transport because it does not require energy from the plant. Symplastic or transcellular is an energy requiring active-transport mechanism for the uptake of nutrients; molecules are bound to carrier proteins to be introduced in the cell via endocytosis. Particle size, hydrophobicity, surface charge, and aggregation are all known to alter NP- cell wall/membrane interactions. Particle size in particular is a determining factor in the uptake of NPs; smaller particles have a greater tendency for long distance transport whereas larger particles, either from original size or through aggregation, more often accumulate in tissues. Cell walls are semipermeable and limit the passage of different molecules, but because pores in plant cell walls have an average size of 3–8 nm, nanoparticles exceeding this size are most likely to be transported by the symplastic pathway. Interaction of the cell wall with particles through endocytosis can lead to formation of pore cavities that facilitate the access of even more particles increasing the uptake of NPs to the plant. A number of studies have demonstrated that nanoparticles of specific chemistries and exceeding a certain size do not translocate at all. For example, most AgNPs with a size up to 40 nm remained adhered to the root caps of seedlings treated for four weeks and did not translocate. Given the ~100 nm size of the LNPs tested herein, we expect translocation to have occurred through the symplastic transport mechanism, with improved translocation due to the negative charge of the particles.

In general, a positive charge is associated with higher NP adsorption on root surfaces and greater NP content in roots, whereas negatively charged NPs are associated with higher internalization rates and translocation efficiency. As noted above, the goal of this study was to improve translocation of a non-systemic agrochemical and as such, the negative charge of the LNPs was desired as a contributing factor to reach this goal. Nanoparticle delivery systems have the potential to be used as tools to improve the effectiveness of agrochemical delivery by facilitating translocation from roots to leaves or vice versa as shown here in a hydroponic system. The interaction of the LNPs with the soil is expected to be different from what was seen in a hydroponic solution due to possible aggregation, degradation and interaction of NPs with soil constituents. These interactions are affected by their particle size, shape, and surface charge, as well as the presence of organic matter, pH, and microorganisms which can affect how particles behave. Because the LNPs have a highly negative charge and no tendency to aggregate under a wide pH range, they are expected to remain in suspension unless they encounter positively charged soil constituents to which they will electrostatically be attracted to. Further studies are required to completely understand their interactions with soil and support the hypothesis that LNPs can shuttle agrochemicals to plants grown in soil. Cadmium is a class-I carcinogen and extremely toxic metal to human being; exposure to Cd primarily damage kidneys and can cause other very serious health problems for the cardiovascular, pulmonary and musculoskeletal systems . Bioaccumulation of Cd in rice grain is a serious concern, particularly in Asian countries where people ingest rice two to three times each day. It is a critical issue for rice because nearly half of the population worldwide is dependent on rice as a dominant staple food . The world noticed its first evidence of Cd poisoning in the 1950s in Japan through the occurrence of the “Itai-Itai disease” caused due to consumption of Cd contaminated rice .

Rice plant has the tendency to amass Cd more efficiently as compared to other cereals and also constitutes the major source of dietary intake of Cd in some countries like China and countries located in the sub-continent including Sri Lanka, India and Bangladesh . Cd is a trace metal without any notable function in the growth and development of animals and plants . Agricultural soils have been contaminated by Cd as a result of anthropogenic activities, for instance metal smelting, fossil fuel incineration, sewage sludge and phosphatic fertilizer application . Cd is readily acquired through roots of crop plants and transferred to the upper parts of the plant, including the grain, and this procedure relies on how much Cd is available in soils as well as the inherent capacity of the plants . Crops that are grown in Cd-polluted soils may have ahigh amount of Cd in their edible portions, and this could be a precursor to consumers risking chronic toxicity if the intake is large enough . Aquatic plants such as the rice plant ,fodder growing system common cattail and common reed release oxygen from root aerenchyma by radial oxygen loss that oxidizes Fe2+ in submerged soils to Fe3+ oxides that precipitate on the surface of the roots in the form of Fe plaque . The presence of Fe plaques on surfaces of wetland plant roots may offer a means of exclusion and attenuation of metals . A study showed that rice varieties with greater radial oxygen loss capacities tended to form higher rates of Fe plaque on the surfaces of roots and hence limiting the transfer of Cd from root to above-ground parts including grain . Dong et al. discovered that Fe plaque formation led to the deposition of heavy metals onto the external surfaces of roots, subsequently restricting Cd in rice tissues being taken up and transferred. A study showed rice tissues Cd content as well as the citrate-bicarbonate-dithionite -Cd of roots were greatly influenced by Fe and Cd supplementation into growth solution . Exogenous Cd addition in the culture solution remarkedly enhanced the concentration of Cd in rice tissue and CBD extracts, and these concentrations were undetectable in the absence of exogenous Cd additions. It was observed that Fe application displayed a significant role in the Cd accumulation and transportation in rice plants and root cells, rather than in the Fe plaque existing around the roots . Another research study revealed that Fe plaque deposited around the root decreased Cd absorption and that Fe addition reduced the harmfulness of Cd to the rice seedlings grown hydroponically . The study confirmed that application of 0.2 mM Fe to the solution of 10 µM Cd did not suppress the root growth of the rice plant and the root and shoot Cd content and translocation of Cd from the nutrient solution to the shoots with a combined treatment of Fe and Cd, were diminished by 34.1%, 36.0% and 20.1%, respectively, compared to only Cd addition. Understanding the root plaque formation and its impact on Cd accumulation for various rice varieties is crucial as this will generate key information on Cd accumulation by rice genotypes to assist in minimizing the human health risks associated with rice consumption.