Auxin plays a central role in control of organ abscission, and it is thought that changes in the auxin gradient across the abscission zone are the primary determinant of the onset of abscission. The nature of this gradient, whether in concentration, flow, or perhaps in the response system has not conclusively been determined. We employed a DR5::GUS auxin response reporter system to examine the temporal and spatial distribution of the auxin response activity in response to developmental and environmental cues during pedicel abscission in tomato. In pedicels of young and fully open flowers, auxin response, as indicated by GUS activity, was predominantly detected in the vascular tissues and was almost entirely confined to the abscission zone (AZ) and to the distal portion of the pedicel, with a striking reduction in the proximal tissues below the AZ—a ‘step’, rather than a gradient. Following pollination and during early fruit development, auxin response increased substantially throughout the pedicel. Changes in GUS activity following treatments that caused pedicel abscission (flower removal, high temperature, darkness, ethylene, or N-1-naphthylphthalamic acid (NPA) treatment) were relatively minor, with reduced auxin response in the AZ and some reduction above and below it. Expression of genes encoding some auxin efflux carriers (PIN) and influx carriers (AUX⁄LAX) was substantially reduced in the abscission zone of NPA-treated pedicels, and in pedicels stimulated to abscise by flower removal. Our results suggest that changes in auxin flow distribution through the abscission zone are likely more important than the auxin response system in the regulation of abscission.

中文翻译：

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番茄花梗脱落诱导过程中生长素的反应和转运

生长素在器官脱落的控制中起核心作用，并且认为整个脱落区的生长素梯度的变化是脱落开始的主要决定因素。这种梯度的性质，无论是浓度、流量还是响应系统，都尚未最终确定。我们聘请了一位DR5::GUS生长素反应报告系统检查番茄花梗脱落过程中生长素反应活性对发育和环境线索的反应的时空分布。在年轻和完全开放的花的花梗中，生长素反应，如 GUS 活性所示，主要在维管组织中检测到，并且几乎完全局限于离区 (AZ) 和花梗的远端部分，显着减少在 AZ 下方的近端组织中——一个“台阶”，而不是一个梯度。授粉后和早期果实发育期间，整个花梗的生长素反应显着增加。导致花梗脱落的处理后 GUS 活性的变化（摘花、高温、黑暗、乙烯、或 N-1-萘基邻苯二甲酸 (NPA) 处理) 相对较小，AZ 中的生长素反应降低，并且在其上方和下方有所减少。编码一些生长素外流载体（PIN）和内流载体（AUX/LAX）的基因的表达在NPA处理的花梗的脱落区和通过去花刺激脱落的花梗中显着降低。我们的研究结果表明，通过脱落区的生长素流量分布的变化可能比生长素反应系统在调节脱落中更重要。