Hormones in Pear Seeds I. Levels of Gibberellins, Abscisic Acid, Phaseic Acid, Dihydrophaseic Acid, and Two Metabolites of Dihydrophaseic Acid in Immature Seeds of Pyrus communis L.1

Abstract

Abstract Seeds from ‘Bartlett’ and ‘Winter Nelis’ and ovules from seedless ‘Bartlett’ pears were collected periodically between 25 days after full bloom and harvest. Extracts were analyzed for hormones by combined gas chromatography-mass spectrometry, using the technique of selected ion current monitoring. Levels of 6 gibberellins were low in all samples prior to appreciable embryo growth (25 days after full bloom). Content of gibberellins A17, A25, A45 and a presumed 3β-hydroxy gibberellin A45 rose dramatically during rapid embryo growth between 65 and 85 days after full bloom, while the gibberellin content of embryoless ovules of ‘Bartlett’ did not change during this period. Two unidentified gibberellin-like compounds, one isomeric with gibberellin A25 and the other corresponding to a hydroxy gibberellin A45, were detected 85 days after full bloom. Abscisic acid content was also maximal between 65 and 106 days, ovules of seedless ‘Bartlett’ exhibiting considerably higher concentration than seeds of either cultivar. Levels of 5 abscisic acid metabolites varied with seed type and sampling period. Phaseic acid levels remained low in ‘Bartlett’ seeds and ovules during all developmental stages but increased in ‘Winter Nelis’ seeds at 122 days. Concentration of cis, Trans-dihydrophaseic acid, although low, rose as ‘Winter Nelis’ seeds matured while ovules of seedless ‘Bartlett’ showed no such increase. Levels of 2 metabolites, tentatively identified as trans, trans-dihydrophaseic acid and a hydroxylated derivative of dihydrophaseic acid, varied only slightly with development. A third metabolite, characterized as a keto derivative of dihydrophaseic acid or a hydroxy-derivative of phaseic acid, was present in large quantities in unfertilized ovules during the early period of fruit growth, but increased in seeds only after 65 days. The possible roles of these compounds are discussed in relation to seed, fruit, and flower development.