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ARS Home » Midwest Area » Urbana, Illinois » Soybean/maize Germplasm, Pathology, and Genetics Research » Research » Publications at this Location » Publication #57873
Title: TRANSLOCATABLE LEAF SIGNAL AUTOREGULATES SOYBEAN NODULATION

Author
item FRANCISCO, PERIGIO - 3611-05-00 (RESIGNED)
item Harper, James

Submitted to: Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/31/1995
Publication Date: N/A
Citation: N/A

Interpretive Summary: Legume plants have the ability to utilize atmospheric nitrogen by converting it to ammonia in specialized root structures termed nodules. Ability to alter nodulation of legumes requires an understanding of the factors which control nodule initiation and development. It has been established that a signal molecule is translocated from the shoot to the root of a legume plant which determines the number of nodules. This study pinpointed the site of this signal to be in the leaf itself, as opposed to the other possibility that it arose from the bud or growing point of the shoot. This finding allows one to concentrate on the leaf to identify the molecule involved in this control of nodule number. Since the signal is common among legume species, identification of this signal potentially has major impact in terms of enhancing nitrogen availability to legume plants without using nitrogenous fertilizers.

Technical Abstract: In soybean [Glycine max (L.) Merr.], expression of hypernodulation phenotype appears to be controlled by the shoot. The current study attempted to localize the source of the nodulation inhibitor in soybean cv. Williams 82 and its hypernodulating mutant NOD1-3. Wedge grafts (replacement of entire shoot) and approach grafts (addition of a shoot) were utilized and the shoot scion treatments ranged from complete shoots to various combinations of leaf, cotyledon, and apex removal from the grafted scion. Leaf-bearing wedge- or approach-grafted scion types dictated the nodulation phenotype of the host plant. Scions with more leaves clearly were more effective in altering nodulation. Scions without apices were as effective in altering nodulation as were scions with both apices and leaves. Leaf and shoot cuttings which were stimulated to form roots were also examined for expression of nodulation. Leaf cuttings, which were devoid of any meristematic apices, exhibited nodulation phenotypes similar to that of the shoot cuttings, i.e., leaf and shoot cuttings of Williams 82 being normally nodulated while those of NOD1-3 were hypernodulated. These observations definitively proved that the leaf, and not the apex, was the synthesis site of a translocatable signal controlling autoregulation of nodule number.