Author
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Harper, James |
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Submitted to: United States Japan Seminar Series
Publication Type: Abstract Only Publication Acceptance Date: 10/30/1995 Publication Date: N/A Citation: N/A Interpretive Summary: Technical Abstract: Grafting studies confirmed root control of nonnodulation expression. Nonnodulation in the NN5 mutant is blocked very early in that root hair curling does not occur, even though attachment of bacteria to root hairs appears normal. Grafting studies also confirmed that a translocatable shoot signal was responsible for hypernodulation, which appears to be involved in release of autoregulatory control of nodule development. Using rooted leaf cuttings, it was definitively shown that the leaf, as opposed to a meristematic apex, was the site of signal generation controlling hypernodulation expression. It is not clear whether autoregulation in normally nodulating cultivars is due to a leaf derived inhibitor which is absent in hypernodulated lines, or whether the hypernodulated lines produce a promoter signal. Effort is currently concentrating on determining if an inhibitor or promoter signal is involved. The identification of a translocatable signal molecule(s) has not yet been successful. It is intriguing that hypernodulation can be induced on Vigna radiata and Lablab purpureus by grafting shoots of a hypernodulated soybean to roots of these two species, suggesting some commonality of signal among legumes. In contrast, Hamaguchi et al (Crop Sci, 33:794, 1993) concluded that the mechanism controlling nodulation or substances involved in autoregulation are different between soybean and Phaseolus vulgaris, again based on interspecie grafts. Additional work is necessary to elucidate the nodulation control mechanism(s) in legumes. |
