Goldental-Cohen S, Burstein C, Biton I, Ben Sasson S, Sadeh A, Many Y, Doron-Faigenboim A, Zemach H, Mugira Y, Schneider D, Birger R, Meir S, Philosoph-Hadas S, Irihomovitch V, Lavee S, Avidan B, Ben-Ari G
Institute of Plant Sciences, ARO, The Volcani Center, 7528809, Rishon LeZion, Israel.
The Robert H. Smith Institute of Plant Sciences and Genetics in Agriculture, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, 76100, Rehovot, Israel.
BMC Plant Biol. 2017 May 16;17(1):87. doi: 10.1186/s12870-017-1035-1.
Table olives (Olea europaea L.), despite their widespread production, are still harvested manually. The low efficiency of manual harvesting and the rising costs of labor have reduced the profitability of this crop. A selective abscission treatment, inducing abscission of fruits but not leaves, is crucial for the adoption of mechanical harvesting of table olives. In the present work we studied the anatomical and molecular differences between the three abscission zones (AZs) of olive fruits and leaves.
The fruit abscission zone 3 (FAZ3), located between the fruit and the pedicel, was found to be the active AZ in mature fruits and is sensitive to ethephon, whereas FAZ2, between the pedicel and the rachis, is the flower active AZ as well as functioning as the most ethephon induced fruit AZ. We found anatomical differences between the leaf AZ (LAZ) and the two FAZs. Unlike the FAZs, the LAZ is characterized by small cells with less pectin compared to neighboring cells. In an attempt to differentiate between the fruit and leaf AZs, we examined the effect of treating olive-bearing trees with ethephon, an ethylene-releasing compound, with or without antioxidants, on the detachment force (DF) of fruits and leaves 5 days after the treatment. Ethephon treatment enhanced pectinase activity and reduced DF in all the three olive AZs. A transcriptomic analysis of the three olive AZs after ethephon treatment revealed induction of several genes encoding for hormones (ethylene, auxin and ABA), as well as for several cell wall degrading enzymes. However, up-regulation of cellulase genes was found only in the LAZ. Many genes involved in oxidative stress were induced by the ethephon treatment in the LAZ alone. In addition, we found that reactive oxygen species (ROS) mediated abscission in response to ethephon only in leaves. Thus, adding antioxidants such as ascorbic acid or butyric acid to the ethephon inhibited leaf abscission but enhanced fruit abscission.
Our findings suggest that treating olive-bearing trees with a combination of ethephon and antioxidants reduces the detachment force (DF) of fruit without weakening that of the leaves. Hence, this selective abscission treatment may be used in turn to promote mechanized harvest of olives.
油橄榄（油橄榄属）尽管产量广泛，但仍采用人工采摘。人工采摘效率低下以及劳动力成本不断上升，降低了这种作物的盈利能力。一种诱导果实而非叶片脱落的选择性脱落处理，对于采用油橄榄机械采摘至关重要。在本研究中，我们研究了油橄榄果实和叶片的三个脱落区（AZs）之间的解剖学和分子差异。
位于果实和果梗之间的果实脱落区3（FAZ3），被发现是成熟果实中的活跃脱落区，且对乙烯利敏感，而位于果梗和叶轴之间的FAZ2，既是花的活跃脱落区，也是乙烯利诱导果实脱落最有效的区域。我们发现叶片脱落区（LAZ）与两个FAZ之间存在解剖学差异。与FAZ不同，LAZ的特点是细胞小，与相邻细胞相比果胶含量少。为了区分果实和叶片的脱落区，我们研究了用乙烯利（一种释放乙烯的化合物）处理油橄榄树，无论有无抗氧化剂，对处理后5天果实和叶片的脱离力（DF）的影响。乙烯利处理增强了所有三个油橄榄脱落区的果胶酶活性并降低了脱离力。对乙烯利处理后的三个油橄榄脱落区进行转录组分析，发现诱导了几个编码激素（乙烯、生长素和脱落酸）以及几种细胞壁降解酶的基因。然而，纤维素酶基因的上调仅在LAZ中发现。许多参与氧化应激的基因仅在LAZ中被乙烯利处理诱导。此外，我们发现活性氧（ROS）仅在叶片中介导对乙烯利的脱落反应。因此，在乙烯利中添加抗氧化剂如抗坏血酸或丁酸可抑制叶片脱落，但增强果实脱落。
我们的研究结果表明，用乙烯利和抗氧化剂组合处理油橄榄树可降低果实的脱离力（DF），而不削弱叶片的脱离力。因此，这种选择性脱落处理可反过来用于促进油橄榄的机械化收获。
