Effects of Auxins on Membrane Permeability and Pectic Substances in Bean Endocarp

Abstract

IT has been shown^1,2 that auxins delay the onset of senescence in bean endocarp and various leaf tissues (Rhoeo, Mesembryanthemum) maintained in vitro. In the absence of auxin, liquid-logging of intercellular spaces is followed by cellular dissociation and rounding off of cells. Similar changes have been observed in the abscission zones of Coleus, Cestrum and Fuchsia. When de-seeded bean pod segments are maintained in Petri dishes on wet filter paper, liquid-logging is evident in 2½–3 days and an exudate appears on the upper tissue surfaces. Cellular dissociation is usually complete by the fifth day. These changes are essentially prevented by the addition of an auxin (3-indoleacetic acid or α-naphtha-leneacetic acid) to the culture medium. There are no significant differences in increase in fresh weight or respiratory activity between water- and auxin-treated endocarp segments over a ten-day period. The cells of liquid-logged segments are still capable of plasmolysis and deplasmolysis. The results indicate that the liquid-logging and exudation are manifestations of changes in permeability. A second process involves changes in the composition of the cell-wall cementing substances which take place in the absence of auxin and give rise to cellular dissociation and rounding off of cells.