Abstract
The important role of auxin polar transport in the early growth stage of etiolated maize (Zea mays L. cv. Honey Bantam) seedlings was intensively studied. Rapid growth in the basal region of coleoptile and the apical region of mesocotyl was observed in etiolated maize seedlings in the dark. Indole-3-acetic acid (IAA) applied to the top of coleoptile substantially promoted the growth of coleoptile and mesocotyl dose-dependently, suggesting that endogenous IAA is responsible for the growth of coleoptile and mesocotyl in etiolated maize seedlings. Polar transport of radiolabeled IAA ([14C]IAA) in the coleoptile segment was significantly higher than that in the mesocotyl segment from etiolated maize seedlings. Auxin polar transport in the coleoptile and mesocotyl segments from etiolated maize seedlings increased with the growth of the seedlings from which the segments were excised. Maximum expression of the gene (ZmPIN1a) closely related to auxin polar transport was observed just prior to maximum levels of auxin polar transport in the coleoptile and mesocotyl segments. In addition, the growth rate was well correlated with the auxin polar transport and the expression of ZmPIN1a gene in coleoptile and mesocotyl of etiolated maize seedlings. These results strongly suggest that auxin polar transport regulated by ZmPIN1a protein is essentially required for the growth of coleoptile and mesocotyl in the early growth stage of etiolated maize seedlings.
