Cultivars of Hexaploid Wheat of Contrasting Stature and Chlorophyll Retention Differ in Cytokinin Content and Responsiveness

Abstract

Abstract The work reported here compared cytokinin content and sensitivity in a selection of hexaploid wheat ( Triticum aestivum L.) cultivars using the following measurements: leaf cytokinins at three time points during light-growth and at four 24 h intervals after light-grown plants were transferred to darkness; sensitivity of root growth to direct applications of isopentenyl adenosine ([9R]iP); and, sensitivity of germination and subsequent root and shoot growth to 18 h imbibition of seeds in benzyladenine (BA). Accumulation of zeatin riboside-type cultivars was greatest during light-growth in Tibet Dwarf, a wheat with an extreme dwarf phenotype, intermediate in Omar standard and dwarf cultivars, and lowest in the standard and dwarf versions of Itana. Cytokinin levels were otherwise not directly correlated to plant stature in these wheats. There were no cultivar-associated qualitative differences in the types of cytokinins detected in this study. During the 16 h light period, the content of zeatin riboside-type cytokinins increased up to tenfold and then declined to basal levels during dark growth. Chlorophyll retention during dark-growth was correlated with leaf cytokinin content. Data collected at a restricted number of sampling points during dark-growth suggested a cyclic accumulation of [9R]iP-type cytokinins and the apparent cycle in Tibet Dwarf was offset by 24 h. Tibet Dwarf showed the greatest root growth inhibition after exposure of seedling roots to [9R]iP or imbibition of seeds in BA. Neither of these treatments affected shoot growth in any of the cultivars.