INHIBITION OF MAIZE PRIMARY ROOT ELONGATION BY SPERMIDINE - EFFECT ONCELL-SHAPE AND MITOTIC INDEX

Spermidine applied for 18 h to intact maize seedlings through their ro ots reduces root growth 70%, and the effect is reversible. Histologica l observations of longitudinal sections of 0.4-cm root apical segments from 2-day-old maize seedlings grown for 18 h in 0.5 mM CaSO4 solutio n with or without 1 mM spermidine contribute to the explanation of spe rmidine-dependent slow root growth, In the meristematic zone a strong reduction of the mitotic index and in the elongation zone an inhibitio n of cell elongation occur simultaneously. Cell shape analysis along t he growth axis of the maize root apex expressed in terms of form facto r (FCircle) values substantiates the dual effect of spermidine on mito tic activity and cell elongation.