IS WALL-BOUND CALCIUM REDISTRIBUTED DURING THE GRAVIREACTION OF STEMSAND COLEOPTILES

We have tested the hypothesis that wall-bound calcium is redistributed from the lower to the upper sides of horizontal stems and coleoptiles during the reaction phase of gravicurvature. We used atomic absorptio n spectrometry to measure wall-bound calcium in the epidermal and inte rnal layers of sunflower (Helianthus annuus L.) hypocotyls and pea (Pi sum sativum L.) epicotyls, and total calcium in maize (Zea mays L.) co leoptiles at the time of maximal gravireaction. In every case, we foun d that there was no measurable redistribution of wall-bound calcium ei ther from the lower to the upper sides, or between epidermal and inner tissues in response to the gravistimulus. These results indicate that a redistribution of wall-bound calcium does not play a role during th e gravireaction of stems and coleoptiles.