Department of Agricultural Sciences, Saga University, Saga, Japan.
Plant Signal Behav. 2010 Apr;5(4):440-3. doi: 10.4161/psb.5.4.10849. Epub 2010 Apr 4.
The phytohormone abscisic acid (ABA) is known to be a negative regulator of legume root nodule formation. By screening Lotus japonicus seedlings for survival on an agar medium containing 70 μM ABA, we obtained mutants that not only showed increased root nodule number, but also enhanced nitrogen fixation. The mutant was designated enf1 (enhanced nitrogen fixation 1) and was confirmed to be monogenic and incompletely dominant. In long-term growth experiments with M. loti, although some yield parameters were the same for both enf1 and wild-type plants, both the dry weight and N content of 100 seeds and entire enf1 plants were significantly larger compared than those traits in wild-type seeds and plants. The augmentation of the weight and N content of the enf1 plants most likely reflects the increased N supplied by the additional enf1 nodules and the concomitant increase in N fixation activity. We determined that the endogenous ABA concentration and the sensitivity to ABA of enf1 were lower than that of wild-type seedlings. When wild-type plants were treated with abamine, a specific inhibitor of 9-cis-epoxycarotenoid dioxygenase (NCED), which results in reduced ABA content, the N fixation activity of abamine-treated plants was elevated to the same levels as enf1. We also determined that production of nitric oxide (NO) in enf1 nodules was decreased. We conclude that endogenous ABA concentration not only regulates nodulation, but also nitrogen fixation activity by decreasing NO production in nodules.
植物激素脱落酸（ABA）是众所周知的豆科植物根瘤形成的负调节剂。通过筛选在含有 70 μM ABA 的琼脂培养基上存活的百脉根幼苗，我们获得了不仅表现出增加的根瘤数，而且增强了固氮的突变体。该突变体被命名为 enf1（增强固氮 1），并被确认为单基因且不完全显性。在与 M. loti 的长期生长实验中，尽管 enf1 和野生型植物的一些产量参数相同，但 100 粒种子和整个 enf1 植物的干重和 N 含量均明显大于野生型种子和植物的这些性状。 enf1 植物的重量和 N 含量的增加很可能反映了额外的 enf1 根瘤提供的更多 N，以及随之而来的固氮活性的增加。我们确定 enf1 的内源 ABA 浓度和对 ABA 的敏感性低于野生型幼苗。当用 abamine（一种 9-顺式-环氧类胡萝卜素双加氧酶（NCED）的特异性抑制剂，导致 ABA 含量降低）处理野生型植物时，abamine 处理的植物的固氮活性升高到与 enf1 相同的水平。我们还确定 enf1 根瘤中一氧化氮（NO）的产生减少。我们得出结论，内源 ABA 浓度不仅通过降低根瘤中 NO 的产生来调节结瘤，还调节固氮活性。
