Heterogeneous Photochemistry of Agrochemicals at the Leaf Surface: A Case Study of Plant Activator Acibenzolar-S-methyl

Abstract

The photoreactivity of plant activator benzo(1,2,3)thiadiazole-7-carbothioic acid S-methyl ester (BTH), commonly named acibenzolar-S-methyl, was studied on the surfaces of glass, paraffinic wax films, and apple leaves. Experiments were carried out in a solar simulator using pure and formulated BTH (BION). Surface photoproducts were identified using liquid chromatography coupled with electrospray ionization and high-resolution Orbitrap mass spectrometry, while volatile photoproducts were characterized using an online thermal desorption system coupled to a gas chromatography-mass spectrometry (GC-MS) system. Pure BTH degraded quickly on wax surfaces with a half-life of 5.0 ± 0.5 h, whereas photolysis of formulated BTH was 7 times slower (t = 36 ± 14 h). On the other hand, formulated BTH was found to photolyze quickly on detached apple leaves with a half-life of 2.8 h ± 0.4 h. This drastic difference in photoreactivity was attributed to the nature and spreading of the BTH deposit, as influenced by the surfactant and surface characteristics. Abiotic stress of irradiated apple leaf was also shown to produce OH radicals which might contribute to the enhanced photodegradability. Eight surface photoproducts were identified, whereas GC-MS analyses revealed the formation of gaseous dimethyl disulfide and methanethiol. The yield of dimethyl disulfide ranged between 1.5% and 12%, and a significant fraction of dimethyl disulfide produced was found to be absorbed by the leaf. This is the first study to report on the formation of volatile chemicals and OH radicals during agrochemical photolysis on plant surfaces. The developed experimental approach can provide valuable insights into the heterogeneous photoreactivity of sprayed agrochemicals and could help improve dissipation models.

Atmospheric Micro and Nanoplastics: An Enormous Microscopic Problem

“…For example, water microalgae are able to grow on MP particles, leading to an increase in the density and facilitating their sinking in sediments, with a transit from water bodies to soil [29]. On the other hand, the comb-out effect is responsible for the deposition of atmospheric MP on the canopy [30], probably facilitated by the wax layer on leaves, which is able to trap hydrophobic pollutants [31]. The study from Scheurer and Bigalke [32] shows that 90% of Swiss floodplain soils contain MP, and the main result is that the mesoplastic concentration is correlated with the presence of bigger plastic waste, while MP were found also in soil not affected by human activity.…”

Volatilomics: a non-invasive technique for screening plant phenotypic traits

“…Methanethiol signals, however, could also be caused by photo-dissociation of BTH at the surface of the plants [44]. To test for this possible additional methanthiol source, we installed plant mock-ups of stainless steel wool in the cuvettes and sprayed them with BTH solution similar as we did in the plant experiments (cf.…”

“…The whole experiment was performed twice using the same BTH solution in order to avoid concentration variations due to systematic errors. In the meanwhile, the solution was stored in the dark to prevent possible photo-dissociation [44].…”

Research on the Interaction Mechanism Between α Mino-Phosphonate Derivative Q-R and Harpin-Binding Protein 1 in Tobacco (Nicotiana tabacum) Plants

“…The chiral α-aminophosphonate derivative Q-R (99%) and dufulin (99%) was synthesized in our laboratory (Zhang et al, 2016). Benzo-1, 2, 3-thiadiazole-7-carbothioic acid S-methyl ester (BTH) (99%) was purchased from Aladdin Biochemical Technology Co. (Shanghai, China) (Sleiman et al, 2017). The structural formulae of these compounds are presented in Figure 1.…”