Spatial and temporal distribution of free and bound ABA in wheat and dandelion ovaries in the period of egg-cell activity

We quantified endogenous free and bound ABA in ovaries of the apomictic Taraxacum officinale Web. (dandelion) and amphimictic Triticum aestivum L. (wheat) species. ABA distribution was assessed in four ovary sections and during three developmental stages: from the quiescence release of the egg-cell until its first division (the period of egg-cell activity). ABA content was determined by the novel modification of the ELISA technique. The ovaries of both species contained approximately similar amounts of free ABA; whereas wheat ovaries contained 1.5 to 2-fold more bound ABA. A possible involvement of the hormonal system in the control of the chronology of the basic events of plant reproduction (egg-cell activation, the onset of endosperm development, the start of embryogenesis) is discussed.