Instituto de Agroquímica y Tecnología de Alimentos (CSIC), Jaime Roig 11, E-46010, Valencia, Spain.
Planta. 1992 Sep;188(2):245-51. doi: 10.1007/BF00216820.
The effect of LAB 198 999 [3,5-dioxo-4-butyryl-cyclohexane carboxylic acid ethyl ester; a new plant growth retardant which competitively inhibits 2-oxoglutarate-dependent gibberellin (GA) dioxygenases] on elongation and in-vivo [(3)H]GA1 and [(3)H]GA20 metabolism in cowpea (Vigna sinensis L. cv Blackeye pea No. 5) epicotyls has been investigated. Gibberellins and LAB 198 999 were injected into the epicotyl at 25-30 mm from the apex. In intact seedlings, epicotyl elongation was inhibited by LAB 198 999 (25 μg · epicotyl(-1)), and the inhibition was counteracted by GA1 but not by GA20. In contrast to intact seedlings, the inhibitor enhanced epicotyl elongation in de-bladed seedlings and expiants, in the latter case proportionally to the amount of inhibitor applied (up to 50 μg · epicotyl(-1)), but not in explants made from paclobutrazol-treated seedlings. The inhibitor also enhanced dramatically the elongation induced in paclobutrazol-treated expiants by GA1, but not by GA20. The promotive effect of LAB 198 999 was associated with increased contents of GA1 and GA8 in the growing region of the epicotyl, indicating a dependence on endogenous GAs. The effect of LAB 198999 decreased progressively with the age of the seedlings, probably as a consequence of a decreased level of GAs in the epicotyl. Gibberellin substrates and metabolites in the growing region of the epicotyl (upper 20 mm) were fractionated and identified tentatively by high-performance liquid chromatography and radiocounting using a homogeneous on-line radioactivity detector. The metabolism of [(3)H]GA1(t) (tentative) to [(3)H]GA8(t), and that of [(3)H]GA20(t) to [(3)H]GA1(t) and [(3)H]GA29(t) in the epicotyl were blocked by LAB 198 999, that of the former more efficiently than the latter. The results presented support the hypothesis that GA1 is the active GA controlling elongation of cowpea epicotyls. They also show that both the promotion of epicotyl elongation in explants and the enhancement of the effect of exogenous GA1 by LAB 198 999 are the result of the inhibitor blocking the in-vivo 2β-hydroxylation of GA1.
LAB 198 999（3,5-二氧代-4-丁酰基环己烷羧酸乙酯；一种新型的植物生长延缓剂，竞争性抑制 2-氧代戊二酸依赖性赤霉素（GA）双加氧酶）对豇豆（Vigna sinensis L. cv. Blackeye pea No.5）下胚轴伸长和体内[3H]GA1和[3H]GA20代谢的影响进行了研究。赤霉素和 LAB 198 999 被注射到离顶端 25-30 毫米的下胚轴处。在完整的幼苗中，LAB 198 999（25μg·下胚轴-1）抑制下胚轴伸长，GA1 可拮抗抑制作用，但 GA20 则不行。与完整的幼苗不同，抑制剂在下胚轴去叶幼苗和外植体中增强了下胚轴伸长，在后一种情况下，与所施加的抑制剂的量成正比（高达 50μg·下胚轴-1），但在来自多效唑处理的幼苗的外植体中则不行。抑制剂还显著增强了多效唑处理的外植体中由 GA1 诱导的伸长，但不能由 GA20 诱导。LAB 198999 的促进作用与下胚轴伸长区 GA1 和 GA8 的含量增加有关，表明对内源性 GAs 的依赖性。LAB 198999 的作用随着幼苗年龄的增加而逐渐降低，可能是由于下胚轴中 GAs 水平降低所致。用高效液相色谱法和放射性计数法，用同种在线放射性检测器对下胚轴伸长区（上 20mm）的赤霉素底物和代谢物进行了分离和初步鉴定。在赤霉素处理的下胚轴中，[3H]GA1（暂定）向[3H]GA8（暂定）的代谢，以及[3H]GA20（暂定）向[3H]GA1（暂定）和[3H]GA29（暂定）的代谢被 LAB 198 999 阻断，前者比后者更有效。所提出的结果支持了 GA1 是控制豇豆下胚轴伸长的活性 GA 的假说。它们还表明，LAB 198 999 促进外植体中下胚轴的伸长以及增强外源性 GA1 的作用，都是由于抑制剂阻断了 GA1 的体内 2β-羟化作用。
