Pedicel abscission of soybean: cytological and ultrastructural changes induced by auxin and ethephon

Abstract

Indole-3-acetic acid delayed the onset of pedicel abscission of soybean, Glycine max (L.) Merrill, by 20 h, and in some experiments, significantly reduced abscission over a 7-day treatment period. Cytological and ultrastructural development of the abscission zone could be divided into two phases: the first associated with longer cells and fewer multigrained amyloplasts in the incipient separation layer; the second with shorter cells (indicative of secondary cell division), increased numbers of amyloplasts, and significant changes in the percent volume of cytoplasm, vacuoles, and wall tissue. Middle lamella dissolution preceded cell separation. Indole-3-acetic acid delayed but did not disrupt the sequence of events leading to abscission. Ethephon treatment hastened abscission but both delayed and disrupted typical abscission events, especially secondary cell division, which occured less frequently. In addition, cellular collapse and greater swelling of cells were observed in the separation layer of ethephon-treated tissue. Key words: abscission, ethylene, Glycine max, indole-3-acetic acid, pedicel, raceme.