Beyer E M
Central Research Department, Experimental Station, E. I. du Pont de Nemours and Company, Wilmington, Delaware 19898.
Plant Physiol. 1975 Feb;55(2):322-7. doi: 10.1104/pp.55.2.322.
The leaf blade of cotton (Gossypium hirsutum L. cv. Stoneville 213) was investigated as the initial site of ethylene action in abscission. Ethylene applied at 14 mul/l to intact 3-week-old plants caused abscission of the third true leaf within 3 days. However, keeping only the leaf blade of this leaf in air during ethylene treatment of the rest of the plant completely prevented its abscission for up to 7 days. This inhibition of abscission was apparently the result of continued auxin production in the blade since (a) the application of an auxin transport inhibitor to the petiole of the air-treated leaf blade restored ethylene sensitivity to the leaf in terms of abscission; (b) repeated applications of naphthaleneacetic acid to the leaf blade of the third true leaf, when the entire plant was exposed to ethylene, had the same preventive effect on abscission of this leaf as keeping its leaf blade in air; and (c) the inhibitory effect of ethylene on auxin transport in the petiole, which is reduced by auxin treatment, was also reduced by placing the leaf blade in air.The reverse treatment of exposing only the leaf blade of the third true leaf to 14 mul/l of ethylene, while the rest of the plant was kept in air, also did not cause abscission for up to 5 days. Auxin transport in the petioles of these leaves, however, was inhibited over 80% within 2 days and this effect presumably accounted for their increased sensitivity to ethylene during the subsequent exposures of the whole leaf to the gas.These results suggest that an initial and essential function of applied ethylene in abscission is to reduce the amount of auxin transported out of the leaf blade. This reduction together with the inhibitory effect of ethylene on auxin transport in the petiole reduces the auxin level at the abscission zone to a point where the cells in this region become responsive to the more direct action of the gas (e.g., enzyme induction and secretion). This sequence of events accounts for the lack of abscission unless ethylene is applied to both the leaf blade and the abscission zone.
以棉花（陆地棉品种斯通维尔213）叶片作为脱落过程中乙烯作用的起始部位进行了研究。以14微升/升的浓度对3周龄完整植株施用乙烯，可在3天内导致第三片真叶脱落。然而，在对植株其余部分进行乙烯处理期间，仅将这片叶子的叶片置于空气中，可使其在长达7天的时间内完全不脱落。这种对脱落的抑制显然是由于叶片中持续产生生长素所致，因为：（a）对置于空气中处理的叶片叶柄施用生长素运输抑制剂，可恢复叶片对乙烯在脱落方面的敏感性；（b）当整株植物暴露于乙烯时，对第三片真叶的叶片重复施用萘乙酸，对这片叶子脱落的预防作用与将其叶片置于空气中相同；（c）将叶片置于空气中也可降低乙烯对叶柄中生长素运输的抑制作用，而生长素处理可减弱这种抑制作用。对第三片真叶仅将其叶片暴露于14微升/升乙烯，而植株其余部分置于空气中的反向处理，在长达5天的时间内也不会导致脱落。然而，这些叶片叶柄中的生长素运输在2天内被抑制了80%以上，这种效应可能解释了在随后整叶暴露于该气体时它们对乙烯的敏感性增加。这些结果表明，施用乙烯在脱落过程中的初始和基本功能是减少从叶片中输出的生长素量。这种减少以及乙烯对叶柄中生长素运输 的抑制作用，将脱落区的生长素水平降低到该区域细胞对该气体更直接作用（如酶诱导和分泌）产生反应的程度。除非乙烯同时施用于叶片和脱落区，否则这一系列事件可解释为何不会发生脱落。
