Da. Phillips et al., Identification of lumichrome as a Sinorhizobium enhancer of alfalfa root respiration and shoot growth, P NAS US, 96(22), 1999, pp. 12275-12280
Citations number
39
Categorie Soggetti
Multidisciplinary
Journal title
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Sinorhizobium meliloti bacteria produce a signal molecule that enhances roo
t respiration in alfalfa (Medicago sativa L.) and also triggers a compensat
ory increase in whole-plant net carbon assimilation. Nuclear magnetic reson
ance, mass spectrometry, and ultraviolet-visible absorption identify the en
hancer as lumichrome, a common breakdown product of riboflavin. Treating al
falfa roots with 3 nM lumichrome increased root respiration 21% (P < 0.05)
within 48 h. A closely linked increase in net carbon assimilation by the sh
oot compensated for the enhanced root respiration. For example, applying 5
nM lumichrome to young alfalfa roots increased plant growth by 8% (P < 0.05
) after 12 days. Soaking alfalfa seeds in 5 nM lumichrome before germinatio
n increased growth by 18% (P < 0.01) over the same period. In both cases. s
ignificant growth enhancement (P < 0.05) was evident only in the shoot. 5.
meliloti requires exogenous CO2 for growth and may benefit directly from th
e enhanced root respiration that is triggered by lumichrome. Thus Sinorhizo
bium-alfalfa associations. which ultimately form symbiotic: N-2-reducing ro
ot nodules, may be favored at an early developmental stage by lumichrome, a
previously unrecognized mutualistic signal. The rapid degradation of ribof
lavin to lumichrome under many physiological conditions and the prevalence
of riboflavin release by rhizosphere bacteria suggest that events demonstra
ted here in the 5. meliloti-alfalfa association may be widely important acr
oss many plant-microbe interactions.