Morphological and Anatomical Effects of Pyrazon on Bean

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Abstract
Bean (Phaseolus vulgarisL., var. Tendercrop) plants treated during germination with 100 ppm 5-amino-4-chloro-2-phenyl-3(2H)-pyridazinone (pyrazon) were indistinguishable from untreated plants until 5 days after seedling emergence. Chlorosis began at the leaf margins, progressed inward, and became more severe until the leaves became necrotic and died. Similar symptoms were observed on leaves of plants treated with 25 and 50 ppm, but they appeared 4 to 10 days later. The light-microscope study of leaf tissue revealed that chloroplast form and arrangement were altered by pyrazon treatment. Chloroplasts in leaves of treated plants became round and swollen rather than discoid, contained no starch, aggregated in clumps, and developed an affinity for safranin stain.