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THE EFFECT OF LACL₃ ON ROOT GROWTH AND MICROTUBULE ORGANIZATION IN PRIMARY ROOTS OF ZEA MAYS L.  M. Liu and K.H. Hasenstein, Biology Dept. UL Lafayette, Lafayette, Louisiana 70504-2451

   The calcium antagonist LaCl₃ was used to study the effect on primary root elongation and the organization of microtubules in maize roots.  The tested concentrations varied from 1 µM to 10mM LaCl₃. Growth was promoted ca. 45% at 1 µM La³⁺ but reduced by 40% at 1 mM or higher. Compared with controls (Mes/Tris buffer, pH 6.2), 100 µM and higher La³⁺ concentrations inhibited root elongation. Although growth inhibition was strongest in the first hour after application, it further increased over time. Immunostaining of microtubules (MT) showed that 1µM LaCl₃ (5 hr) stabilized MT orientation perpendicular to the root axis. However, LaCl₃ greater than100 µM caused disruption of MT in cortical and epidermal cells of the elongation zone and reduced mitotic activity and density of MT in the apical region. After 24 hrs, cortical MT in the elongation zone were severely depolymerized. Our results indicate that La³⁺‑induced growth inhibition is concentration and time dependent. The MT reorganization after La-treatment suggests that La-mediated growth may interfere with calcium fluxes across the plasma membrane and affect calcium-dependent signal transduction and growth.

(Supported by NASA grant NAG10-0190.)