Nitrogenase activity of sugar cane propagated from stem cuttings in sterile vermiculite |
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| Authors: | DG Patriquin LA Gracioli AP Ruschel |
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| Institution: | Centro de Energia Nuclear na Agricultura, CX. Postal 96, Piracicaba 13400, São Paulo, Brazil |
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| Abstract: | About one-quarter of 6- to 15-day old sugar cane (cv NA56-79) propagated from surface sterile or untreated single node cuttings in sterile vermiculite exhibited acetylene-reducing activity (ARA). Most of this ARA was in the rhizosphere vermiculite. There was no ARA before sprouting of the cuttings. There were numerous nitrogen-fixing and other bacteria in macerated untreated and macerated surface sterile cuttings, and nitrogen-fixers were enriched when small sections taken from internal tissues of cuttings were incubated on sucrose agar slants under air. Possible sites of N2-fixers in the stem tissues, and possible routes of movement of these bacteria into the rhizosphere after germination were indicated by observations of distributions of tetrazolium-reducing bacteria. There was no evidence of progressive invasion of the stem from the surface inwards. It is suggested that the most likely origin of bacteria in the stem is in the root interior where tetrazolium-reducing bacteria were observed in the same types of sites as in the stems, viz. in intercellular spaces and in the xylem. Reestablishment of the stem bacteria in the roots and rhizosphere soil following germination appears to constitute an instance of cyclic infection. This phenomenon may be of significance historically, and potentially, to perpetuate and enhance N2 fixation by sugar cane. |
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