Sarquis J I, Morgan P W, Jordan W R
Department of Soil and Crop Sciences, Texas A & M University, College Station, Texas 77840.
Plant Physiol. 1992 Apr;98(4):1342-8. doi: 10.1104/pp.98.4.1342.
We investigated the metabolism of 1-aminocyclopropane-1-carboxylic acid (ACC) in etiolated maize (Zea mays L.) seedlings subjected to mechanical impedance by applying pressure to the growing medium. Total concentrations of ACC varied little in unimpeded seedlings, but impeded organs accumulated ACC. Roots had consistently higher concentrations of ACC than shoots or seeds, regardless of treatment. The concentration of ACC in the roots increased more than 100% during the first hour of treatment irrespective of the pressure applied; in shoots, total ACC concentration increased 46% at either low or high pressure during the first hour of treatment. The bulk of ACC synthesized under impeded and unimpeded conditions was present in a conjugated form, presumably, 1-(malonylamino)-cyclopropane-1-carboxylic acid. However, 1-(malonylamino)-cyclopropane-1-carboxylic acid increased 73% over controls after 10 hours at 25 kilopascals of pressure. Unimpeded tissue had about 77% ACC as the conjugate and 17% as free ACC, and less than 6% was used in ethylene production. Increased amounts of ACC were converted into ethylene under stress. In vivo ACC synthase activity in roots became six and seven times higher only 1 hour after initiation of treatment at 25 and 100 kilopascals of pressure, respectively, and remained high for at least 6 hours. However, the immediate and massive conjugation of mechanically induced ACC suggests that ACC N-malonyltransferase may play an important role in the regulation of mechanically induced ethylene production. After 8 hours, in vivo activity of the ethylene-forming enzyme complex increased 100 and 50% above normal level at 100 and 25 kilopascals, respectively. Furthermore, ethylene-forming enzyme complex activity was significantly greater at 100 kilopascals than in controls as early as 1 hour after treatment initiation. These data suggest that regulation of ethylene production under mechanical impedance involves the concerted action of ACC synthase, the ethylene-forming enzyme complex, and ACC N-malonyltransferase.
我们通过对生长培养基施加压力，研究了遭受机械阻抗的黄化玉米（Zea mays L.）幼苗中1-氨基环丙烷-1-羧酸（ACC）的代谢情况。在未受阻碍的幼苗中，ACC的总浓度变化不大，但受阻碍的器官会积累ACC。无论处理如何，根部的ACC浓度始终高于地上部分或种子。在处理的第一个小时内，无论施加何种压力，根部的ACC浓度都会增加超过100%；在地上部分，在处理的第一个小时内，无论低压还是高压，总ACC浓度都会增加46%。在受阻碍和未受阻碍条件下合成的大部分ACC以共轭形式存在，推测为1-（丙二酰氨基）-环丙烷-1-羧酸。然而，在25千帕的压力下处理10小时后，1-（丙二酰氨基）-环丙烷-1-羧酸比对照增加了73%。未受阻碍的组织中约77%的ACC为共轭形式，17%为游离ACC，用于乙烯生成的不到6%。在胁迫条件下，更多的ACC转化为乙烯。在25和100千帕的压力下处理仅1小时后，根部的体内ACC合酶活性分别比初始时高出6倍和7倍，并至少保持6小时的高水平。然而，机械诱导的ACC立即大量共轭表明，ACC N-丙二酰转移酶可能在调节机械诱导的乙烯生成中起重要作用。8小时后，在100和25千帕的压力下，乙烯形成酶复合物的体内活性分别比正常水平高出100%和50%。此外，早在处理开始1小时后，100千帕压力下的乙烯形成酶复合物活性就明显高于对照。这些数据表明，在机械阻抗下乙烯生成的调节涉及ACC合酶、乙烯形成酶复合物和ACC N-丙二酰转移酶的协同作用。
