Control of nodule number by the phytohormone abscisic Acid in the roots of two leguminous species.
The effects of the phytohormone abscisic acid (ABA) on plant growth and root nodule formation were analyzed in Trifolium repense (white clover) and Lotus japonicus, which form indeterminate and determinate nodules, respectively. In T. repense, although the number of nodules formed after inoculation with Rhizobium leguminosarum bv. trifolii strain 4S (wild type) was slightly affected by exogenous ABA, those formed by strain H1(pC4S8), which forms ineffective nodules, were dramatically reduced 28 days after inoculation (DAI). At 14 and 21 DAI, the number of nodules formed with the wild-type strain was decreased by exogenous ABA. In L. japonicus, the number of nodules was also reduced by ABA treatment. Thus, exogenous ABA inhibits root nodule formation after inoculation with rhizobia. Observation of root hair deformation revealed that ABA blocked the step between root hair swelling and curling. When the ABA concentration in plants was decreased by using abamine, a specific inhibitor of 9-cis-epoxycarotenoid dioxygenase, the number of nodules on lateral roots of abamine-treated L. japonicus increased dramatically, indicating that lower-than-normal concentrations of endogenous ABA enhance nodule formation. We hypothesize that the ABA concentration controls the number of root nodules.
Department of Chemistry and Bioscience, Faculty of Science, Kagoshima University, Kagoshima, 890-0065 Japan. azuki@sci.kagoshima-u.ac.jp
Akihiro
A
Suzuki
Mitsumi
M
Akune
Mari
M
Kogiso
Yoshihiro
Y
Imagama
Ken-Ichi
K
Osuki
Toshiki
T
Uchiumi
Shiro
S
Higashi
Sun-Young
SY
Han
Shigeo
S
Yoshida
Tadao
T
Asami
Mikiko
M
Abe
D000040:Abscisic Acid / Q000378:metabolism* / Q000494:pharmacology; D049308:Dioxygenases; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D000070116:Lotus / Q000187:drug effects / Q000254:growth & development* / Q000378:metabolism; D010105:Oxygenases / Q000037:antagonists & inhibitors / Q000378:metabolism; D010940:Plant Proteins; D018517:Plant Roots / Q000187:drug effects / Q000254:growth & development* / Q000378:metabolism; D011930:Reaction Time / Q000187:drug effects / Q000502:physiology; D016961:Rhizobium leguminosarum / Q000502:physiology; D013559:Symbiosis / Q000187:drug effects / Q000502:physiology; D029921:Trifolium / Q000187:drug effects / Q000254:growth & development* / Q000378:metabolism
D004791:Enzyme Inhibitors; D010940:Plant Proteins; D000040:Abscisic Acid; D010105:Oxygenases; D049308:Dioxygenases; C109043:9-cis-epoxy-carotenoid dioxygenase