Growth inhibition of sourgrass as a function of period of darkness after diquat application

Abstract

Photosystem-inhibiting herbicides, such as diquat, act by inducing oxidative stress. However, oxidative damage impairs translocation, resulting in regrowth of the plants. The aim was to evaluate the effectiveness of diquat in controlling the growth of sourgrass exposed to different periods of darkness after application of the herbicide, as well as to evaluate the photosynthetic activity and the production of reactive oxygen species. Two experiments (field and greenhouse) were conducted by applying diquat (200 g a.i. ha-1) on sourgrass plants at the 3 to 4 tiller stage. The treated plants were subjected to different periods of darkness after diquat application (0, 1, 2, 3, 4, 5, and 6 h), in addition to the control treatment without any application. Growth inhibition and mass evaluations of the sourgrass plants were performed in both experiments, whereas photosynthetic activity and H2O2 accumulation in the leaves were evaluated in the greenhouse experiment. The results showed an increase in the sourgrass growth inhibition with an increase in the period of darkness after application. There was a need for a minimum of 6 h of darkness after diquat application to fully inhibit growth (100%) of the sourgrass, whereas plants that remained in the sun since application exhibited less than 50% inhibition. The increase in the period of darkness after diquat application resulted in a reduction in photosynthetic activity and, consequently, lower accumulation of H2O2. Thus, the maintenance of sourgrass in the dark for at least 6 h enables total control of the growth of the plants, preventing regrowth.

Chemical Desiccation in the Preharvest of Cowpea: A Study of How the Time of Application Interferes in the Enzymatic and Physiological Aspects of Seedlings from Desiccated Plants

“…After the leaf uptake process, both diquat and paraquat capture all cellular free electrons generated by the metabolic pathways of respiration and photosynthesis, rapidly triggering the formation of free radicals responsible for membrane peroxidation. 36 Consequently, symptoms of chlorosis, followed by necrosis, are observed hours after the application of these herbicides to sensitive plants. 37 The herbicides saflufenacil and glyphosate also anticipated cowpea harvest, but 3 days less compared to treatments with diquat.…”

“…•− ), hydroxyl radical (OH • ) and hydrogen peroxide (H 2 O 2 ). 36 The cell death caused by diquat is due to the accumulation of EROS, thus generating oxidative stress that drives lipid peroxidation. 66 In contrast, flumioxazin and carfentrazone act by inhibiting the enzyme protoporphyrinogen oxidase (PROTOX), which is involved in chlorophyll biosynthesis by catalyzing the oxidation of protoporphyrinogen IX to protoporphyrin IX.…”

“…The higher efficacy of herbicides that inhibit photosystem I to anticipate harvest may be related to the rapid action of these herbicides. After the leaf uptake process, both diquat and paraquat capture all cellular free electrons generated by the metabolic pathways of respiration and photosynthesis, rapidly triggering the formation of free radicals responsible for membrane peroxidation . Consequently, symptoms of chlorosis, followed by necrosis, are observed hours after the application of these herbicides to sensitive plants …”

“…Diquat is an herbicide of the bipyridyl group that acts by diverting the flow of electrons from photosystem I (PSI) and competes with ferredoxin to bind to PSI . From this, a reaction of these electrons with molecular oxygen occurs and the formation of reactive oxygen species (ROS) such as superoxide anion (O 2 •– ), hydroxyl radical (OH • ) and hydrogen peroxide (H 2 O 2 ) . The cell death caused by diquat is due to the accumulation of EROS, thus generating oxidative stress that drives lipid peroxidation .…”