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Auxin Transport in Secondary Tissues
by Rupert Sheldrake
Journal of Experimental Botany, Vol.24, No.78, pp. 87-96, February 1973

Abstract: Auxin transport was investigated in excised stem segments of Nicotiana tabacum L. by the agar block technique using (I-14C) indol-3yl-acetic acid (IAA). The ability of the stems to transport auxin basipetally increased as secondary development proceeded; by contrast the ability of the pith to transport auxin declined with age. By separation of the stem tissues it was shown that the great majority of auxin transport took place in cells associated with the internal phloem and in cells close to the cambium; in both cases similar velocities of transport were found (c 5.0 mm h-1 at 22°C). The effects of osmotic gradients on auxin transport through the internal phloem were investigated. IAA was found by chromatography to account for practically all the radioactivity in receiver blocks and ether extracts of stem segments. The significance of these results is discussed.