Prolongation of Embryo Sac Viability in Pear (Pyrus communis) Following Pollination or Treatment with Gibberellic Acid

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Abstract
Embryo sac development has been investigated in unpollinated, cross pollinated and gibberellic acid (GA2) treated flowers of Pyrus communis L. While pollination and GA3 treatments do not alter embryo sac development, they prolong embryo sac viability. In untreated unpollinated flowers, ovules degenerate between 12 and 21 d after anthesis, while in cross pollinated and GA3 treated flowers this degeneration is postponed by about 10 d. Thus, in a cross pollinated flower this extends the period over which a successful fertilization can take place. This increased period of viability is accompanied by an elongation of the embryo sac itself. Elongation takes place two weeks prior to fertilization in cross pollinated flowers. The extension of life span of embryo sacs following pollination and treatment with gibberellic acid indicates that a stimulus induced by ‘pollination’ could be mediated by GA3 Whatever its mechanism of operation, the prolongation of embryo sac viability by pollination represents a selective advantage, in that the period at which the ovules are receptive to fertilization must be significantly extended.