Distribution of Indole-3-Acetic Acid in the Apoplast and Symplast of Squash {Cucurbita maxima) Hypocotyls

The concentration of endogenous IAA was higher in an apoplastic solution (2.3xlO~7M) than in a symplas-tic solution (0.5 x 10~7 M) obtained from segments of etio-lated squash (Cucurbita maxima Duch.) hypocotyls. Ex-ogenously applied IAA (10~5 M) increased the level of IAA in both the apoplastic and the symplastic solution. The con-centration of IAA in the apoplastic solution increased to 75 % of the concentration of exogenous IAA in 4 h, but that in the symplastic solution increased only to 23 % of the concentration of exogenous IAA. These results demon-strate that the concentration of endogenous IAA is higher in the apoplast than in the symplast of squash hypocotyls, and they suggest that IAA exerts its physiological effects, at least to some extent, from the outside of cells. Key words: Apoplast — Cucurbita maxima — Hypocotyl