Researchers at the University of Cambridge have revealed in a new study that
the plant hormone gibberellin (GA) is essential for the formation and
maturation of nitrogen-fixing root nodules in legumes and can also increase
nodule size.



In the research results published in The Plant Cell, Dr. Alexander Jones'
research group at the Sainsbury Laboratory Cambridge University (SLCU) and
Professor Giles Oldroyd's group at the Crop Science Centre have made a major
step by revealing the GA dynamics that govern the development, morphology
and function of nitrogen-fixing root nodules. Dr. Jones said that their
experiments showed that adding GA reduces nodulation and removing GA
increases nodulation in legumes such as Medicago truncatula. This suggests
that GA is antagonistic towards nodulation, but there is also a legume
mutant in peas that produces less GA and has fewer nodules, which suggests
that GA is somehow required for nodulation. "These conflicting results
suggest there is probably something going on with spatial-temporal GA
patterning," Dr. Jones added.



Using the highly sensitive next-generation biosensor nlsGIBBERELLIN
PERCEPTION SENSOR 2 (GPS2) developed in the Jones Group, Dr. Colleen Drapek
was able to visualize exactly where and when GA was present and in what
relative concentrations it occurred. She found that GA accumulated in the
nodule primordium (the zone in the root cortex where cells start dividing in
the early stages of nodule formation) in Medicago infected with rhizobium
bacteria. Dr. Drapek used GA and symbiotic Medicago mutants to further test
what GA was doing by targeting the overexpression of enzymes that break GA
down or synthesize GA. The result for the former was that no nodules were
formed and the latter was with larger nodules.



[www.slcu.cam.ac.uk]
ns-critical-role-legume-nitrogen-fixation