Abstract While the ethylene-auxin interactions are well documented in model dicots such as tomato (climacteric fruit) during mature fruit abscission, the process is not clearly understood in citrus (non-climacteric fruit). The mature fruit produces very little ethylene but is sensitive to ethylene treatments to induce abscission. By contrast, auxin treatments delay fruit abscission, but the particular role of auxin in the process is unknown. Since the IDA-HAE/HSL2 ethylene-independent pathway seem to regulate organ abscission in both model and crop species, we proposed that auxin treatment delays citrus fruit abscission by reactivating the basipetal auxin flux and reducing CitIDA3 expression, without modifying ethylene synthesis. Comparing orange (C. sinensis) genotypes which differ in their abscission rate, ‘Navelate’ vs. ‘Valencia Late’, we found that the force needed to detach the fruit from the tree (FDF) declines in parallel with 1) an increase of ethylene synthesis and CitIDA3 gene expression, and 2) a reduction of PIN1-like (auxin transporter) gene expresion. Further, auxin (2,4-D) treatment maintains a higher force in the abscission zone upregulating PIN1-like and AUX1-like (auxin transporter) gene expression, and downregulating CitIDA3 gene expression, but without modifying ethylene production. We conclude that the 2,4-D treatment delays citrus mature fruit abscission through an ethylene-independent pathway.

中文翻译：

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柑橘成熟脱落过程中生长素、乙烯和IDA-肽的关系

摘要 虽然在成熟果实脱落过程中，乙烯-生长素相互作用在模型双子叶植物（如番茄（跃变果实））中得到了充分记录，但在柑橘（非跃变果实）中，该过程尚不清楚。成熟的果实产生很少的乙烯，但对乙烯处理敏感以诱导脱落。相比之下，生长素处理延迟果实脱落，但生长素在该过程中的特殊作用尚不清楚。由于 IDA-HAE/HSL2 乙烯非依赖性途径似乎调节模型和作物物种的器官脱落，我们提出生长素处理通过重新激活基叶生长素通量和减少 CitIDA3 表达来延迟柑橘类水果的脱落，而不改变乙烯合成。比较脱落率不同的橙色 (C. sinensis) 基因型，“脐带”与“瓦伦西亚晚”，我们发现将果实从树上分离所需的力 (FDF) 与 1) 乙烯合成和 CitIDA3 基因表达的增加以及 2) PIN1 样（生长素转运蛋白）基因表达的减少同时下降。此外，生长素 (2,4-D) 处理在脱落区保持较高的力，上调 PIN1 样和 AUX1 样（生长素转运蛋白）基因表达，并下调 CitIDA3 基因表达，但不改变乙烯产量。我们得出结论，2,4-D 处理通过不依赖乙烯的途径延迟了柑橘成熟果实的脱落。4-D) 处理在脱落区保持较高的力，上调 PIN1 样和 AUX1 样（生长素转运蛋白）基因表达，并下调 CitIDA3 基因表达，但不改变乙烯产量。我们得出结论，2,4-D 处理通过不依赖乙烯的途径延迟了柑橘成熟果实的脱落。4-D) 处理在脱落区保持较高的力，上调 PIN1 样和 AUX1 样（生长素转运蛋白）基因表达，并下调 CitIDA3 基因表达，但不改变乙烯产量。我们得出结论，2,4-D 处理通过不依赖乙烯的途径延迟了柑橘成熟果实的脱落。