2,4-Dichlorophenoxyacetic acid functionalized gold nanoparticles: synthesis, characterization and biological effects.

Understanding and visualizing the biodistribution of agricultural chemicals inside cells and living plants is very important for enhancing targeting and changing the application approaches of chemicals. Here, a novel material was synthesized through 2,4-dichlorophenoxyacetic acid functionalized small gold nanoparticles (2,4-D-MP-Au NPs). The successful modification of Au NPs (4.46 ± 0.70 nm) was ascertained by UV-vis, TEM, FTIR and XPS. TGA data revealed about 1197 molecules of 2,4-D were coupled to the surface of one Au nanoparticle, which was sufficient for bioapplications. The optical imaging of 2,4-D-MP-Au NPs inside BY-2 cells was directly examined, revealing that 2,4-D-MP-Au NPs could be internalized in BY-2 cells by the two-photo microscopy and endocytosis, as the internalization mechanism was energy dependent for 2,4-D-MP-Au NPs. Furthermore, the biodistribution of 2,4-D-MP-Au NPs in Ricinus cotyledons was measured, revealing that 2,4-D-MP-Au NPs could enter into mesophyll cells of Ricinus cotyledons; the cell recognition was enhanced after 2,4-D conjugated Au NPs. These results indicate that the conjugates have great potential for applications on bioimaging and biolabeling for agricultural chemicals in plant physiology.

Synthesis of a series of monosaccharide-fipronil conjugates and their phloem mobility.

To test the effect of adding different monosaccharide groups to a non-phloem-mobile insecticide on the phloem mobility of the insecticide, a series of conjugates of different monosaccharides and fipronil were synthesized using the trichloroacetimidate method. Phloem mobility tests in castor bean ( Ricinus communis L.) seedlings indicated that the phloem mobility of these conjugates varied markedly. L-Rhamnose-fipronil and D-fucose-fipronil displayed the highest phloem mobility among all of the tested conjugates. Conjugating hexose, pentose, or deoxysugar to fipronil through an O-glycosidic linkage can confer phloem mobility to fipronil in R. communis L. effectively, while the -OH orientation of the monosaccharide substantially affected the phloem mobility of the conjugates.

Uptake and phloem transport of glucose-fipronil conjugate in Ricinus communis involve a carrier-mediated mechanism.

Some compounds containing glucose are absorbed via the monosaccharide transporters of the plasma membrane. A glucose-fipronil conjugate, N-[3-cyano-1-[2,6-dichloro-4-(trifluoromethyl)phenyl]-4-[(trifluoromethyl)sulfinyl]-1H-pyrazol-5-yl]-1-(ß-d-glucopyranosyl)-1H-1,2,3-triazole-4-methanamine (GTF), has been synthesized in our previous work. GTF exhibits moderate phloem mobility in Ricinus communis. In the current paper, we demonstrate that the uptake of GTF by Ricinus seedling cotyledon discs is partly mediated by an active carrier system (K(m)1 = 0.17 mM; V(max)1 = 2.2 nmol cm(-2) h(-1)). Four compounds [d-glucose, sucrose, phloridzin, and carbonyl cyanide m-chlorophenylhydrazone (CCCP)] were examined for their effect on GTF uptake. Phloridzin as well as CCCP markedly inhibit GTF uptake, and d-glucose weakly competes with it. The phloem transport of GTF in Ricinus seedlings is found to involve an active carrier-mediated mechanism that effectively contributes to the GTF phloem loading. The results prove that adding a glucose core is a reasonable and feasible approach to confer phloem mobility to fipronil by utilizing plant monosaccharide transporters.

Synthesis of glucose-fipronil conjugate and its phloem mobility.

Phloem-mobile insecticides are preferred to achieve economically useful activity. However, only a few phloem-mobile synthetic insecticides are available. One approach to converting nonmobile insecticides into phloem-mobile types is introducing sugar to the parent compound. To test whether the addition of a glucose group to a non-phloem-mobile insecticide enables conversion into phloem-mobile, N-[3-cyano-1-[2,6-dichloro-4-(trifluoromethyl)phenyl]-4-[(trifluoromethyl)sulfinyl]-1H-pyrazol-5-yl]-1-(ß-D-glucopyranosyl)-1H-1,2,3-triazole-4-methanamine (GTF) was prepared through click chemistry. A phloem-mobility test in Ricinus communis L. seedlings confirmed that GTF was mobile in the sieve tubes. Although GTF exhibited lower insecticidal activity against the third-instar larvae of Pzlutella xylostella than fipronil did, it can be reconverted into fipronil in adult plants of castor bean, thereby offsetting the decrease of insecticidal activity. Therefore, the presence of a glucose core confers phloem mobility to fipronil.