Diselenide derivatives as photosystem II inhibitors

Selenium is an essential micronutrient to the metabolism of some plants and toxic to others. The relation between nutrition and toxicity is determined by the metabolism of each plant species and the concentration and oxidation state of selenium.[1] The high concentration of selenium in plants affords growth inhibition, chlorosis, withering and leaf drying, as well as decreased the synthesis of proteins leading to plant death.[2] In this context, we set out to evaluate the organoselenium compounds A1 (diphenyl diselenide) and A2 (1,2-bis(4-chlorophenyl)diselane) as photosystem II (PSII) inhibitors through chlorophyll a (Chl a) fluorescence assay. Based on the experimental data, the OJIP transient polyphasic curve was obtained, which correlates the main events of the photosynthetic apparatus: absorption (ABS), energy trapping (TR), electron transport (ET) and heat dissipation (DI), which occur by reaction center (RC) and cross section (CS), producing the performance index (PI(abs)) and quantum (PH) parameters.[3] Compound A1 reduced PI(abs) parameter by 75%, indicating a damage to photosynthetic process, which decreases the plant development and vitality. Additionally, the reduction of PHI(P0) and PHI(E0) parameters by 37 and 41%, respectively, indicating the electron transport chain was inhibited. The ABS, TR and ET by RC parameters were decreased by 20, 49, 52%, respectively, corroborating the same behaviour of TR0 and ET0 by cross-section parameters that reduced by 35 and 42%, respectively. These results suggest that the absorbed energy in these sections was reduced by the action of A1, indicating the blockage in electron transport.[3] Compound A2 does not show significantly variation on the photosynthetic parameters. Thus, the organoselenium compound A1 have shown to be promising photosynthesis inhibiting agent and may be important probe in the development of new materials with herbicidal activity.