Enhanced nodulation and nitrogen fixation in the abscisic acid low-sensitive mutant enhanced nitrogen fixation1 of Lotus japonicus.
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 microM ABA, we obtained mutants that not only showed increased root nodule number but also enhanced nitrogen fixation. The mutant was designated enhanced nitrogen fixation1 (enf1) and was confirmed to be monogenic and incompletely dominant. The low sensitivity to ABA phenotype was thought to result from either a decrease in the concentration of the plant's endogenous ABA or from a disruption in ABA signaling. We determined that the endogenous ABA concentration of enf1 was lower than that of wild-type seedlings, and furthermore, when wild-type plants were treated with abamine, a specific inhibitor of 9-cis-epoxycarotenoid dioxygenase, which results in reduced ABA content, the nitrogen fixation activity of abamine-treated plants was elevated to the same levels as enf1. We also determined that production of nitric oxide in enf1 nodules was decreased. We conclude that endogenous ABA concentration not only regulates nodulation but also nitrogen fixation activity by decreasing nitric oxide production in nodules.
Department of Agricultural Sciences, Faculty of Agriculture, Saga University, Saga 840-8502, Japan.
Akiyoshi
A
Tominaga
Maki
M
Nagata
Koichi
K
Futsuki
Hidetoshi
H
Abe
Toshiki
T
Uchiumi
Mikiko
M
Abe
Ken-ichi
K
Kucho
Masatsugu
M
Hashiguchi
Ryo
R
Akashi
Ann M
AM
Hirsch
Susumu
S
Arima
Akihiro
A
Suzuki
D000040:Abscisic Acid / Q000378:metabolism / Q000494:pharmacology*; D003433:Crosses, Genetic; D035264:Flowers / Q000187:drug effects / Q000502:physiology; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D005799:Genes, Dominant / Q000235:genetics; D017343:Genes, Plant / Q000235:genetics*; D000070116:Lotus / Q000187:drug effects* / Q000235:genetics* / Q000254:growth & development / Q000382:microbiology; D050505:Mutant Proteins / Q000302:isolation & purification / Q000378:metabolism; D009154:Mutation / Q000235:genetics*; D009569:Nitric Oxide / Q000378:metabolism; D009586:Nitrogen Fixation / Q000187:drug effects* / Q000235:genetics; D010641:Phenotype; D055170:Plant Root Nodulation / Q000187:drug effects* / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012231:Rhizobium / Q000187:drug effects / Q000502:physiology; D053204:Root Nodules, Plant / Q000187:drug effects / Q000378:metabolism; D013559:Symbiosis / Q000187:drug effects; D013997:Time Factors
D050505:Mutant Proteins; D012333:RNA, Messenger; D009569:Nitric Oxide; D000040:Abscisic Acid