DHAKA MARCH 9, 2014. IN AN ARTICLE TITLED, “LIGNIN MODIFICATION LEADS TO INCREASED NODULE NUMBERS IN ALFALFA,” PUBLISHED IN THE MARCH 2014 ISSUE OF PLANT PHYSIOLOGY, VOL. 164(3): 1139-1150, RICHARD A. DIXON, THE LEAD INVESTIGATOR AND EIGHT OF HIS ASSOCIATES HAVE SHOWN THAT REDUCTION OF LIGNIN LEVELS IN ALFALFA (MEDICAGO SATIVA) BY DOWN-REGULATION OF THE MONOLIGNOLBIOSYNTHETIC ENZYME HYDROXYCINNAMOYL COENZYME A:SHIKIMATEHYDROXYCINNAMOYL TRANSFERASE (HCT) RESULTS IN INCREASED DIGESTIBILITY AND PROCESSING ABILITY OF LIGNOCELLULOSES. THE AUTHORS HAVE ALSO NOTED THAT INCREASED DIGESTIBILITY IS OFTEN ASSOCIATED WITH DWARFING AND OTHER CHANGES IN PLANT GROWTH.
THE AUTHORS HAVE FURTHER OBSERVED THE IMPACT OF LIGNIN MODIFICATION ON THE UNDERGROUND ORGANS SUCH AS ROOTS AND NODULES OF ALFALFA PLANTS. WHETHER GROWN IN THE FIELD OR IN THE GREENHOUSE THE AFFECTED ALFALFA PLANTS SHOW A STRIKING REDUCTION IN ROOT GROWTH CONCOMITANT WITH AN INCREASE IN NODULE NUMBERS. THIS PHENOTYPE IS ASSOCIATED WITH INCREASED LEVELS OF GIBBERELLINS AND CERTAIN FLAVONOID COMPOUNDS IN ROOTS. THE RESEARCH RESULTS REPORTED HERE INDICATE THAT IT IS UNLIKELY THAT THE ALTERED GROWTH PHENOTYPE OF REDUCED-LIGNIN ALFALFA IS A DIRECT RESULT OF CHANGES IN NODULATION OR NITROGEN FIXATION EFFICIENCY.