Dobert R C, Rood S B, Zanewich K, Blevins D G
Interdisciplinary Plant Group, Agronomy Department, University of Missouri, Columbia, Missouri 65211.
Plant Physiol. 1992 Dec;100(4):1994-2001. doi: 10.1104/pp.100.4.1994.
Lima bean (Phaseolus lunatus L.) plants inoculated with Bradyrhizobium sp. strain 127E14 displayed a period of marked internode elongation that was not observed in plants inoculated with other compatible bradyrhizobia, including strain 127E15. When strain 127E14 nodulated an alternate host, cowpea (Vigna unguiculata L. Walp), a similar, although less dramatic growth response induced by the bacteria was observed. It has been speculated that the elongative growth promotion brought about by inoculation with strain 127E14 is mediated by gibberellins (GAs). Using deuterated internal standards and gas chromatography-mass spectroscopy analysis, we have quantified the levels of GA(1), GA(20), GA(19), and GA(44) in nodules and stems of two varieties of lima bean (bush and pole) and one variety of cowpea that were inoculated with either strain 127E14 or 127E15. In nodules formed by strain 127E14 on lima bean, endogenous levels of GA(20) and GA(19) were 10 to 40 times higher (35-88 ng/g dry weight) than amounts found in nodules formed by strain 127E15 (2.2-3.9 ng/g dry weight). Relative amounts of GA(44) were also higher (4- to 11-fold) in 127E14 nodules, but this increase was less pronounced. The rhizobial-induced increase of these GAs in the nodule occurred in both pole and bush varieties and seemed to be independent of host morphology. Regardless of rhizobial inoculum, levels of the "bioactive" GA(1) in the nodule (0.3-1.1 ng/g dry weight) were similar. In cowpea nodules, a similar, although smaller, difference in GA content due to rhizobial strain was observed. The concentration of GA(1) in lima bean stems was generally higher than that observed in the nodule, whereas concentrations of the other GAs measured were lower. In contrast with the nodule, GA concentrations in lima bean stems were not greater in plants inoculated with strain 127E14, and in some cases the slower growing plants inoculated with strain 127E15 actually had higher levels of GA(20), GA(19), and GA(44). Thus, there were major differences in concentrations of the precursors to GA(1) in nodules formed by the two bacterial strains, which were positively correlated with the observed elongation growth. These results support the hypothesis that the rhizobial strain modifies the endogenous GA status of the symbiotic system. This alteration in GA balance within the plant, presumably, underlies the observed growth response.
接种慢生根瘤菌属菌株127E14的利马豆（菜豆）植株出现了一段明显的节间伸长时期，而接种其他兼容慢生根瘤菌（包括菌株127E15）的植株则未观察到这种现象。当菌株127E14在替代宿主豇豆（豇豆）上结瘤时，观察到细菌诱导了类似但不太显著的生长反应。据推测，接种菌株127E14带来的伸长生长促进作用是由赤霉素（GAs）介导的。我们使用氘代内标和气相色谱 - 质谱分析，对两种利马豆品种（矮生和蔓生）以及一种豇豆品种的根瘤和茎中GA(1)、GA(20)、GA(19)和GA(44)的水平进行了定量，这些植株分别接种了菌株127E14或127E15。在利马豆上由菌株127E14形成的根瘤中，GA(20)和GA(19)的内源水平比菌株127E15形成的根瘤中高10至40倍（35 - 88 ng/g干重）（2.2 - 3.9 ng/g干重）。GA(44)在127E14根瘤中的相对含量也更高（4至11倍），但这种增加不太明显。根瘤菌诱导的这些赤霉素在根瘤中的增加在蔓生和矮生品种中均出现，并且似乎与宿主形态无关。无论接种何种根瘤菌，根瘤中“生物活性”GA(1)的水平（0.3 - 1.1 ng/g干重）相似。在豇豆根瘤中，也观察到由于根瘤菌菌株导致的GA含量有类似但较小的差异。利马豆茎中GA(1)的浓度通常高于根瘤中观察到的浓度，而测量的其他赤霉素浓度则较低。与根瘤不同，接种菌株127E14的利马豆茎中的GA浓度并不更高，在某些情况下，接种菌株127E15生长较慢的植株实际上GA(20)、GA(19)和GA(44)的水平更高。因此，两种细菌菌株形成的根瘤中GA(1)前体的浓度存在重大差异，这与观察到的伸长生长呈正相关。这些结果支持了根瘤菌菌株改变共生系统内源GA状态的假设。植物体内GA平衡的这种改变大概是观察到的生长反应的基础。
