198 research outputs found

    Leaf curl syndrome of pigeonpea (Cajanus cajan (L.) Millsp.) is a systemic response to effective nodulation by the Rhizobium strain IC3342

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    Rhizobium str. IC3342 is an unusual bacterium that causes a leaf curl syndrome in pigeonpea. Growth characteristics, plasmid profile, conserved nif and nod gene sequences and nodulation host range of this strain resemble that of the fast-growing Rhizobium str. ANU240 (NGR234). Leaf curl occurred only in hosts effectively nodulated. A plasmid-cured, non-nodulating derivative failed to induce leaf curl symptoms. The str. IC3342 competed poorly with fast- and slow-growing root-nodule bacteria, but the observed nodule occupancy of 10% was enough to produce leaf curl symptoms. Suppression of nodule development by added inorganic nitrogen also prevented symptom expression. Approach grafting of a healthy pigonpea plant with leaf curl symptoms resulted in the development of leaf curl symptoms on the growing shoots of the healthy plant within 8 days of graft union. Further symptom expression ceased after graft separation. Feeding xylem sap from the leaf curled plant to a healthy plant induced the initial symptom of the syndrome, bending of the growing leaf tip. It is concluded that leaf curl induction is a systemic response for which effective nodulation is an apparent prerequisit

    Translocation of zeatin riboside and zeatin in soybean explants

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    Soybean explants consisting of a leaf, one or more young pods, and a subtending piece of stem were given a 1-h pulse of 3 H (ring-labeled)-zeatin riboside (ZR) or -zeatin (Z), via the base of the stem, followed by a 24-h incubation. At the end of the pulse, about 55% of the soluble 3 H was in the leaf blades, 11% in the petiole, 30% in the stem, 2% in the carpels, 0.1% in the seed coats, and 0.08% in the embryos. After 24 h, the percentages were 58, 7, 26, 6, 2, and 0.3, respectively. During this period, the total soluble 3 H decreased by 84%, the remainder being bound to “insoluble” material. The 3 H-cytokinin was rapidly converted to diverse metabolites including adenosine and adenine. At the end of the 1-h pulse, appreciable percentages (1–16%) of the total soluble 3 H in the seed coats chromatographed with ZR (or dihydro ZR) and with the 5′-phosphate of ZR, but these percentages declined markedly at 24 h. No distinct peaks of 3 H corresponded to known metabolites in the soluble extracts of embryos, and at 24 h, the 3 H equivalent to ZR must have been less than 0.0006% of the 3 H-ZR supplied. The bound 3 H corresponded to adenine and guanine in DNA and RNA. In contrast to cytokinin, 3 H-adenosine given as a pulse was readily translocated into the seed coats and embryos. Thus, cytokinin (ZR and Z) flowing up through the xylem from the root system does not readily enter the embryo (though metabolites such as adenosine could), and the seeds clearly do not compete with the leaves for this supply of cytokinin.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/45929/1/344_2005_Article_BF02042255.pd

    Metabolic control of embryonic dormancy in apple seed: seven decades of research

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