The Time‐course of Polar Movement of Gibberellin Through Zea Roots

Abstract

The polarity of movement of gibberellin through sections cut from near the root tips of Zea mays L. was studied, using methods like those we previously used in roots for auxin and in petioles for auxins, cytokinins, and gibberellic acid (GA‐3). One μg GA‐3 was added in a donor agar block and gibberellin activity in the receiver agar at the opposite end of the section was measured directly with a modified barley endosperm bioassay. The movement of gibberellin was away from the root tip (basipetal) and thus opposite in direction to the polarity of auxin through such root sections. The time‐course of basipetal movement was dissimilar to that for gibberellin or auxin movement through petiole sections. It took 14‐18 hr for gibberellin activity equivalent to 6 ng GA‐3 to collect in the basal receivers on roots. Apical receivers showed activity equivalent to 1.6 ng GA‐3 at 14‐18 hr. Less than 0.01 ng equivalent GA‐3 was collected from sections to which GA‐3 was not added, so the 6 and 1.6 ng were almost entirely due to the added GA‐3. These general conclusions were confirmed with an experiment using 14C‐GA‐3. A decline in activity in receivers was found in some experiments at 18 hr, paralleling earlier results with GA‐3, IAA, and adenine in petioles and IAA in roots.

Role of Auxin and Gibberellin in Differentiation of Primary Phloem Fibers

“…Recently, plant hormones other than auxins have been demonstrated to move in a polar fashion through the plant tissues (18,20,21,26). Gibberellic acid which has been shown to move with basipetal polarity through sections cut from young petioles of the Princeton clone of Coleus blumei (18,20) is known to affect primary phloem fiber differentiation (9,34,36,37).…”

Polarity of Thiamine Movement through Tomato Petioles

“…After it was shown (7,8,11,16) that even the synthetic auxin-type herbicide 2, 4-D moved through excised shoot tissues with a polarity like that of the endogenous auxin IAA, other classes of hormones were tested. Just recently, GA. was found to move with a polarity very similar to IAA through Coleus petioles and with opposite polarity to IAA through corn root sections (12)(13)(14). Although early reports claimed polar movement of abscisic acid and a cytokinin (1, 4), the more quantitative later studies found sizeable movement in both directions, with no clear sign of polarity of these two classes of hormone (5,9,18 considered as confirmation of the hypothesis that in the intact plant thiamine was synthesized in the leaves and moved from there to the roots, which were unable to synthesize it but needed it for development.…”