Changes in Free and Bound Auxin with Development of Squares and Bolls in Relation to Shedding

Abstract

Hormone analyses were conducted to determine why large squares seldom shed while young bolls do. Large squares contained five times as much free auxin as flowers, and they contained 16 times as much bound auxin. The high auxin content of large squares is probably a major reason that they almost never shed unless injured (for example, by insects). Free and bound auxin both decreased to very low levels at flowering and remained low for four days thereafter. This low concentration of auxin at, and just after, flowering is probably a major reason that bolls are likely to shed during the week after flowering. Both free and bound auxin increased rapidly between 7 and 9 days after flowering, possibly accounting for the decrease in boll shedding rate at this stage of development. Amide-linked IAA was the major form of auxin in squares, whereas ester IAA (presumably bound to sugars) was the major form of auxin in bolls.