Electronmicrographs of barnyardgrass (Echinochloa crusgalli (L.) Beauv.) grown under controlled conditions and treated with 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine) at the one to three-leaf stages show that degradation of the chloroplast starts as a swelling of the fret system followed by swelling and disruption of the granal discs. In advanced stages of breakdown, the membranes of the grana and chloroplast envelope were ruptured. These changes were initiated 2 hr after treatment with rates of 2, 5, 10, and 20 ppm atrazine. The incidence of starch grains greatly decreased as the duration of treatment exceeded 4 hr. The mitochondria appeared normal throughout, not being affected by concentration or duration of treatment. The stage of growth at which plants were treated was insignificant in determining changes at the ultrastructural level. The ultrastructural changes preceded any macroscopically discernable symptoms of tissue breakdown.

Reduction of 3-Amino-l,2,4-triazole Phytotoxicity in Tomato PlantsThe phytotoxicity of 3-amino-1,2,4-triazole was studied using tomato plants to determine the efficacy of selected compounds in reducing growth and chlorophyll toxicities. When the concentration of 3-AT was 1 X 10-4M, equimolar solutions of certain purine precursors simultaneously applied caused a reduction of 3-AT growth inhibition; but this did not occur when all concentrations were five times this amount. Adenine, hypoxanthine, and guanine and their ribosides acted like the purine precursors. Riboflavin, FMN, and FAD reduced not only 3-AT growth inhibition at 5 X 10-4M, but also the inhibition of chlorophyll formation. A hypothesis of the mechanism of 3-AT phytotoxicity is presented.