Increase of cotton cotyledon resistance to the herbicide endothall by abscisic acid

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Abstract
The herbicide endothall (7‐oxabicyclo 2.2.1 heptane‐2, 3‐dicarboxylic acid) was applied to cotton (Gossypium hirsutum L. cv. Acala SJ‐1) cotyledon discs. Treatment with 10−4M endothall for 24 h resulted in injury which was expressed by increased leakage of electrolytes, development of necrotic areas, increased level of polyphenols and tissue browning. We examined whether treatments which decrease chilling injury would also decrease injury caused by the herbicide. Tissue from seedlings grown at 28°C was more sensitive to endothall than that from seedlings grown at 15°C. Pretreatment with 10−5M abscisic acid greatly decreased the leakage of electrolytes, necrotic areas, and tissue browning caused by endothall. Similar pretreatment did not prevent the increase of polyphenols caused by the herbicide. The treatment with abscisic acid was more effective in protection against the herbicide injury when applied several hours prior to the herbicidal treatment. This time requirement indicates that the mechanism by which abscisic acid induces resistance to the herbicide depends, at least partially, on active metabolism. We suggest that the increased resistance to herbicide stress by abscisic acid is another example of a common resistance mechanism to various stresses in which abscisic acid is involved.