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Articles

Relationship Between Metabolism and the Lateral Transport of IAA in Corn Coleoptiles ¹

School of Biological Sciences, University of East Anglia, Norwich, NOR 77H, U.K.

The lateral movement of IAA in coleoptiles of Zea mays has been investigated under aerobic and anaerobic conditions. The IAA-1-¹⁴C was supplied asymmetrically to the apical end of the segment. The results were as follows: A) In air more ¹⁴C was found in the lower half of horizontal segments supplied with an upper donor than in the half opposite the donor in vertical segments. The enhanced lateral movement of ¹⁴C in geotropically stimulated segments of corn coleoptiles under aerobic conditions has thus been confirmed. B) This increased lateral movement of ¹⁴C in geotropically stimulated segments is greatly reduced, but is not completely abolished, under anaerobic conditions. C) The lateral movement of ¹⁴C in vertical segments is significantly less under anaerobic conditions than in air. D) Under anaerobic conditions, the lateral movement of ¹⁴C in horizontal segments can be reduced to the level found in vertical segments by pre-soaking the tissue in a 1 mM solution of the metabolic inhibitor sodium fluoride for 2 hours. The inhibitor has no effect on lateral movement of ¹⁴C in vertical anaerobic segments. E) In air, sodium fluoride has no effect on the lateral movement of ¹⁴C in either vertical or horizontal segments.

On the assumption that the movement of ¹⁴C reflects the movement of IAA, these results show that the enhanced polarized lateral movement of IAA observed in horizontal corn coleoptile segments is totally abolished only when both aerobic and anaerobic metabolism are arrested. In addition, there appears to be a small metabolically dependent component in the lateral movement of IAA in vertical segments supplied with an asymmetric donor in air.

³ Present address: 17 Lloyd Road, Taverham, Norwich, Norfolk, U.K.

¹ This research was supported by grant No. 83/6 of the U.K. Agricultural Research Council.