Changes in the chlorophyll contents of leaves and in levels of cytokinins in root exudates during ripening of rice [Oryza sativa] cultivars Nipponbare and Akenohoshi
1995
Soejima, H. (Tokyo Univ. of Agriculture and Technology, Fuchu (Japan). Faculty of Agriculture) | Sugiyama, T. | Ishihara, K.
Changes in fluxes of cytokinins in exudates transported via the xylem from roots of rice plants cvs. Nipponbare and Akenohoshi were measured by mass spectrometry with deuterium-labeled standards. The fluxes of zeatin (Z), trans-ribosylzeatin (trans-RZ), N6-isopentenyladenine (iP), and "conjugated Z" (Z in the hydrolyzates of highly polar fractions) decreased from heading to the late ripening stage in both cultivars. At the late ripening stage, iP and Z could no longer be detected, while the flux of N6-isopentenyladenosine (iPA) increased slightly. In Akenohoshi, conjugated Z was the predominant cytokinin from heading to the middle of the ripening stage. The flux of each of the cytokinins in Akenohoshi was higher than that in Nipponbare at every time point, with the exception of the flux of iPA just after heading. The total concentration of cytokinins in the xylem exudate of Akenohoshi was higher than that of Nipponbare after the middle or ripening stage. The chlorophyll content of the third leaves, which were senescing rapidly, was significantly correlated with the flux of total cytokinins per plant or per unit leaf area. These results suggest that the larger amounts of cytokinins, in particular conjugated Z, transported from the roots to the shoots caused the slow senescence of leaves in Akenohoshi during the ripening stage
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