The feedback mechanism of nitrate inhibition of nitrogenase activity in soybean may involve asparagine and/or products of its metabolism
The feedback mechanism of nitrate inhibition of nitrogenase activity in soybean may involve asparagine and/or products of its metabolism
复制标题
DOI：
10.1034/j.1399-3054.1997.1000220.x
复制
发表时间：
1997-06-01
影响因子：
6.4
通讯作者：
Harper, JE
中科院分区：
文献类型：
--
作者：
Bacanamwo, M;Harper, JE
有人提出了一种反馈机制，它涉及到韧皮部N浓度的变化的传感器，以控制在外部结合N存在下的固氮和固氮。这种控制是响应于总氮的变化还是响应于某些特定信号化合物的变化尚不清楚。在本研究中，我们重新评估了假设，即控制植物生长和固氮涉及到组织氮成分变化的传感，并试图确定潜在的信号分子参与。两种大豆（Glycine max [L.]梅尔）根瘤数和耐硝性不同的基因型（威廉姆斯82和NOD 1 -3）在砂盘中萌发。用大豆慢生根瘤菌的溶液接种7天龄的幼苗，并在生长室中生长28天，使用具有有限N供应的水培系统来促进生长。一半的28天龄的植物用15 mM NO3-处理，然后在固氮酶抑制开始时（NO3-处理后24小时）对对照和处理过的植物进行取样，以评价固氮酶活性和组织中总氮和每种游离氨基酸的浓度。异硫氰酸苯酯-（PITC）氨基酸衍生物使用HPLC分离和定量。短期硝酸盐处理后的固氮酶活性的下降与一个显着的天冬酰胺浓度的增加，在拍摄和结节天冬氨酸和谷氨酸在两种基因型的增加。在威廉姆斯82中，芽中的天冬酰胺浓度从几乎检测不到的95 nmol g（-1）鲜重增加到3327 nmol g（-1）鲜重，增加了35倍，在NOD 1 -3中从509 nmol g（-1）鲜重增加到1753 nmol g（-1）鲜重，增加了两倍多。在短期的硝酸盐处理后，在地上部中的游离Asn和总游离氨基酸的水平的增加在威廉姆斯82中比在其部分耐硝酸盐的突变体NOD 1 -3中更明显。这些结果表明，反馈控制的根瘤活动可能涉及感测的变化，在芽天冬酰胺水平和/或其代谢产物（天冬氨酸和谷氨酸）的结节。这些结果也表明，部分硝酸盐耐受hyperoxidulated NOD 1 -3突变体中的oxidulation与硝酸盐处理后组织N的变化较小有关。
A feedback mechanism which involves sensing of change in phloem N concentration has been proposed to control nodulation and dinitrogen fixation in the presence of external combined N. Whether this control is in response to a change in total N or in some specific signal compound(s) is not known. In the present study we reevaluated the hypothesis that control of nodulation and N,fixation involves sensing of change in tissue N composition and attempted to identify potential signal molecule(s) involved. Two soybean (Glycine max [L.] Merr.) genotypes (Williams 82 and NOD1-3) differing in nodule number and tolerance to nitrate were germinated in sand trays. Seven-day-old seedlings were inoculated with a solution of Bradyrhizobium japonicum and grown for 28 days in growth chambers, using a hydroponic system with limited N supply to promote nodulation. Half of 28-day-old plants were treated with 15 mM NO3-, then control and treated plants were sampled at the onset of nitrogenase inhibition (24 h following NO3- treatment) for evaluation of nitrogenase activity and tissue concentration of total N and of each individual free amino acid. Phenylisothiocyanate- (PITC) amino acid derivatives were separated and quantified using HPLC. The decline in nitrogenase activity following the short-term nitrate treatment was associated with a dramatic asparagine concentration increase in the shoot and an increase in nodule aspartate and glutamate in both genotypes. Asparagine concentration in the shoot increased 35 times from a barely detectable level of 95 to 3327 nmol g(-1) fresh weight in Williams 82, and more than tripled from 509 to 1753 nmol g(-1) fresh weight in NOD1-3. Increase in levels of free Asn and in total free amino acids in the shoot following the short-term nitrate treatment was more pronounced in Williams 82 than in its partially nitrate-tolerant mutant NOD1-3. These results indicate that the feedback control of nodule activity may involve sensing changes in shoot asparagine levels and/or products of its metabolism (aspartate and glutamate) in the nodule. These results also indicate that partial-nitrate tolerance of nodulation in the hypernodulated NOD1-3 mutant is associated with a lesser change in tissue N following nitrate treatment.