Young L M, Evans M L
Department of Biological Sciences, Ohio Northern University, Ada 45810, USA.
Plant Growth Regul. 1996;20:253-8. doi: 10.1007/BF00043315.
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.
由于脱落酸（ABA）和生长素（IAA）都被认为可能是根向地性过程中差异生长的化学介质，我们比较了玉米根向地性过程中施用的³H-IAA和³H-ABA的标记再分布情况，并研究了施用于垂直根根尖的³H-IAA和³H-ABA的相对向基运动。³H-ABA在垂直根根尖的横向移动是非极性的，比³H-IAA的横向移动（也是非极性的）大约大2倍。ABA的移动性更强并非由于吸收增强，因为³H-IAA的吸收大于³H-ABA。通过测量施用90分钟后根尖后方连续1毫米切片中的放射性，确定了施用于根冠的³H-IAA或³H-ABA的标记向基运动。ABA主要保留在第一毫米（施用点），而IAA集中在距根尖2 - 4毫米的区域，在距根尖7 - 8毫米处也发现有大量IAA。用极性生长素运输抑制剂预处理会降低重力弯曲和IAA的向基运动。当根水平放置时，相对于从下往上的移动，³H-IAA从上到下穿过根冠的移动增强，而³H-ABA标记的移动模式不受影响。这些结果与IAA在根向地性中起作用的假设一致，但与重力诱导的ABA不对称分布有助于该反应的观点相反。
