title: Patterns of auxin and abscisic acid movement in the tips of gravistimulated primary roots of maize.
abstract: Because both abscisic acid (ABA) and auxin (IAA) have been suggested as possible chemical mediators of differential growth during root gravitropism, we compared with redistribution of label from applied 3H-IAA and 3H-ABA during maize root gravitropism and examined the relative basipetal movement of 3H-IAA and 3H-ABA applied to the caps of vertical roots. Lateral movement of 3H-ABA across the tips of vertical roots was non-polar and about 2-fold greater than lateral movement of 3H-IAA (also non-polar). The greater movement of ABA was not due to enhanced uptake since the uptake of 3H-IAA was greater than that of 3H-ABA. Basipetal movement of label from 3H-IAA or 3H-ABA applied to the root cap was determined by measuring radioactivity in successive 1 mm sections behind the tip 90 minutes after application. ABA remained largely in the first mm (point of application) whereas IAA was concentrated in the region 2-4 mm from the tip with substantial levels found 7-8 mm from the tip. Pretreatment with inhibitors of polar auxin transport decreased both gravicurvature and the basipetal movement of IAA. When roots were placed horizontally, the movement of 3H-IAA from top to bottom across the cap was enhanced relative to movement from bottom to top whereas the pattern of movement of label from 3H-ABA was unaffected. These results are consistent with the hypothesis that IAA plays a role in root gravitropism but contrary to the idea that gravi-induced asymmetric distribution of ABA contributes to the response.
authors.affiliation: Department of Biological Sciences, Ohio Northern University, Ada 45810, USA.
authors.forename: L M
authors.initials: LM
authors.lastname: Young
authors.forename: M L
authors.initials: ML
authors.lastname: Evans
mesh_terms: D000040:Abscisic Acid / Q000493:pharmacokinetics*; D018522:Gravitropism / Q000502:physiology*; D006540:Herbicides / Q000493:pharmacokinetics; D007210:Indoleacetic Acids / Q000037:antagonists & inhibitors / Q000493:pharmacokinetics*; D010797:Phthalimides / Q000493:pharmacokinetics; D010937:Plant Growth Regulators / Q000493:pharmacokinetics*; D018518:Plant Root Cap / Q000254:growth & development / Q000378:metabolism*; D018517:Plant Roots / Q000254:growth & development / Q000378:metabolism; D003313:Zea mays / Q000254:growth & development / Q000378:metabolism*
chemical_list: D006540:Herbicides; D007210:Indoleacetic Acids; D010797:Phthalimides; D010937:Plant Growth Regulators; C002687:alpha-naphthylphthalamic acid; C030737:indoleacetic acid; D000040:Abscisic Acid