The Herbicide Atrazine Potentiates Angiotensin II-Induced Aldosterone Synthesis and Release From Adrenal Cells

Atrazine is one of the most commonly used pre-emergence and early post-emergence herbicides in the world. We have shown previously that atrazine does not directly stimulate the pituitary or adrenal to trigger hormone release but acts centrally to activate a stress-like activation of the hypothalamic-pituitary-adrenal axis. In doing so, atrazine treatment has been shown to cause adrenal morphology changes characteristic of repeated stress. In this study, adrenals from atrazine treated and stressed animals were directly compared after 4 days of atrazine treatment or restraint stress. Both atrazine and stressed animals displayed reduced adrenocortical zona glomerulosa thickness and aldosterone synthase (CYP11B2) expression, indicative of repeated adrenal stimulation by adrenocorticotropic hormone. To determine if reduced CYP11B2 expression resulted in attenuated aldosterone synthesis, stressed and atrazine treated animals were challenged with angiotensin II (Ang II). As predicted, stressed animals produced less aldosterone compared to control animals when stimulated. However, atrazine treated animals had higher circulating aldosterone concentrations compared to both stressed and control groups. Ang II-induced aldosterone release was also potentiated in atrazine pretreated human adrenocortical carcinoma cells (H295R). Atrazine pretreated did not alter the expression of the rate limiting steroidogenic StAR protein or angiotensin II receptor 1. Atrazine treated animals also presented with higher basal blood pressure than vehicle treated control animals suggesting sustained elevations in circulating aldosterone levels. Our results demonstrate that treatment with the widely used herbicide, atrazine, directly increases stimulated production of aldosterone in adrenocortical cells independent of expression changes to rate limiting steroidogenic enzymes.

EFFECTS OF SELECTIVE HERBICIDE, ATRAZINE ON THE RHIZOBIUM POPULATION AND NODULATION OF GROUNDNUT (ARACHIS HYPOGEAE)

Atrazine is a selective herbicide used to control weeds in farm operations. The effect of different concentrations of atrazine on Rhizobium population and nodulation in groundnut (Arachis hypogeae) was investigated using Yeast Extract Mannitol Agar (YEMA). The test crop was planted for 90 days after the soil was treated with the various concentration of atrazine. The following parameters; Rhizobium count, nodule count, plant height and germination percentage were observed. The total Rhizobium count obtained at 0% atrazine treatment has 3.0 x 108, 0.1% has 2.9 x 108, 0.5% has 2.5 x 108, 1% has 2.0 x 108, and 3% has 1.4 x 108 all in cfu/ml while the number of root nodules formed was also counted after uproot which was; 0% atrazine treated has 50 nodules, 0.1% has 50 nodules, 0.5% has 30 nodules, 1% has 23 nodules and 3% has 19 nodules. The study revealed that the higher the atrazine concentration the lower the population of Rhizobium, the numbers of root nodules increased with decrease in atrazine concentration and Plant height, root length and germination percentage was also affected adversely by increased in atrazine concentrations.

Effects of Sub-Lethal Atrazine Concentrations on Embryogenesis, Larval Survival and Growth of African Catfish, Clarias gariepinus (Burchell, 1822)

The toxicity of environmentally relevant concentrations of atrazine on exposed fertilized eggs of Clarias gariepinus was evaluated in a 96hour static non-renewal bioassay. After exposure to atrazine concentrations of 0 (control), 4, 8, 12, and 16 μgL1 in water, first mitotic cleavage in the control occurred at 40 minutes after fertilization. The first cleavage did not occur in the 8 μgL-1 treatment group until 60 minutes after fertilization. Similar dose depended delayed cleavage was observed across atrazine exposed eggs. The first larvae emerged 22 hours from the time of fertilization at 27.00C in both control and atrazine treatment groups. However, hatching rates significantly differed between the control and atrazine exposed eggs (P<0.05) with 73.3% hatching rate in the control and 3.3% among the exposed eggs treated with 16μgL-1 of atrazine. Among the morphological deformities observed in the larvae of atrazine exposed eggs, kyphosis occurred more frequently with 60% of emerged larvae in the 16 μgL-1 atrazine treated group exhibiting the deformity. Morphometry showed significantly reduced head length, body length, body weight, and yolk diameter in 16 μgL-1 atrazine exposed eggs compared to the control. These results indicate that atrazine disrupted embryonic process and delayed hatching with severe larvae deformities.

Atrazine affects craniofacial chondrogenesis and axial skeleton mineralization in zebrafish (Danio rerio)

Atrazine is a commonly used herbicide that has previously been implicated as an endocrine-disrupting compound. Previous studies have shown that estrogenic endocrine-disrupting compounds affect the development of the heart, cartilage, and bone in zebrafish ( Danio rerio). To determine whether atrazine has effects similar to other endocrine disruptors, zebrafish embryos were treated with a range of atrazine concentrations. Atrazine treatment at a low concentration of 0.1 µM resulted in significant differences in craniofacial cartilage elements, while concentrations ≥1 µM led to decreased survival and increased heart rates. Fish treated with ≥1 µM atrazine also developed with delayed vertebrae mineralization. Higher concentrations of atrazine caused gross craniofacial defects and decreased hatching rates. Further studies into the molecular pathways disrupted in these developmental processes could shed light on a link between endocrine-disrupting compounds and developmental abnormalities.

Tank Mixing Pendimethalin with Pyroxasulfone and Chloroacetamide Herbicides Enhances In-Season Residual Weed Control in Corn

Kochia, common lambsquarters, and wild buckwheat are major problem weeds in glyphosate-resistant corn production in the northern Great Plains of the United States. Field research was conducted in 2011 and 2012 near Huntley, MT to investigate effective PRE herbicides applied alone or in premixes with or without tank-mixed pendimethalin for extended in-season residual control of the selected broadleaf weeds in glyphosate-resistant corn. Control of kochia, common lambsquarters, and wild buckwheat with recently registered herbicide premixes, including saflufenacil + dimethenamid-P andS-metolachlor + mesotrione, was as high as 95 and 90% at 21 and 63 d after treatment (DAT), and mostly similar to the standard atrazine treatment. Residual control of common lambsquarters and wild buckwheat from pyroxasulfone was higher at 298 compared with 149 g ai ha−1rate. Pyroxasulfone and other chloroacetamide herbicides (acetochlor or dimethenamid-P) applied alone failed to provide greater than 79, 70, and 54% residual control at 21, 35, and 63 DAT, respectively, of the weed species investigated. Residual weed control throughout the growing season was significantly improved with the addition of pendimethalin to pyroxasulfone (149 g ha−1), acetochlor, or dimethenamid-P when compared with any of the three herbicides applied alone. Kochia control by pyroxasulfone, acetochlor, or dimethenamid-P tank mixed with pendimethalin was as high as 94, 92, and 81% at 21, 35, and 63 DAT, respectively. Control of common lambsquarters with the addition of pendimethalin to pyroxasulfone or acetochlor was improved to 94, 89, and 81% at 21, 35, and 63 DAT, respectively. Similarly, wild buckwheat control with acetochlor plus pendimethalin was improved to 87, 85, and 82% at 21, 35, and 63 DAT, respectively. Consistent with the extended in-season (up to 9 wk) residual weed control, pyroxasulfone, acetochlor, or dimethenamid-P treatments when tank mixed with pendimethalin had higher corn yields compared with the herbicides applied alone. The investigation on residual herbicides that provide extended in-season weed control should be continued as an important aspect of glyphosate stewardship and to mitigate the occurrence of glyphosate-resistant weed populations in grower fields.

Physiological and Molecular Characterization of Atrazine Resistance in a Wild Radish (Raphanus raphanistrum) Population

This study documents the physiology and genetics of evolved atrazine resistance in a wild radish population from Western Australia. Plant response to atrazine treatment confirmed a high level of resistance in population WARR5. At 0.25 kg atrazine/ha, all plants from a susceptible population were killed, whereas resistant WARR5 was unaffected at the highest dose tested (4 kg atrazine/ha). Leaf photosynthesis in susceptible plants was inhibited after 1 kg atrazine/ha treatment, whereas leaf photosynthesis in WARR5 plants was unaffected. Furthermore, atrazine resistance was maternally inherited. Sequencing of apsbAgene fragment in resistant WARR5 and susceptible plants revealed a single point mutation resulting in a coding change from Ser264to Gly of the D1 protein in resistant plants. We are confident that this mutation is the basis of resistance to the photosystem II inhibitors in this wild radish population.

Timing of atrazine application for control of quackgrass (Agropyron repens)

The use of foliar or soil applied atrazine to control quackgrass (Agropyron repens) in corn (Zea mays) was investigated. Atrazine treatments to control quackgrass significantly increased corn yield. Spring tillage without atrazine had little or no long term effect on quackgrass stand. A single application of 4.5 kg a.i. atrazine ha-1 applied in the fall or spring provided no better control of quackgrass than a split application of 2.25 kg a.i. atrazine ha-1 in either the foliage or bare soil experiments. Quackgrass recovery and soybean (Glycine max) yield were measured for 2 yr afterthe last atrazine application. Quackgrass did not recover to any significant extent within 2 yr after the cessation of the treatments on any of the atrazine treated plots. Atrazine residues from the previous fall applications significantly reduced soybean yield. Two years after the last atrazine treatment, soybean yields were similar, regardiess of former spring or fall atrazine application.