CHANGES OF ENDOGENOUS HORMONE LEVELS IN DEVELOPING SEEDS, ZYGOTIC EMBRYOS AND MEGAGAMETOPHYTES IN PICEA-GLAUCA

Endogenous free abscisic acid (ABA), indole-3-acetic acid (IAA) and gi bberellins (GAs) were identified and quantified in whole white spruce (Picea glauca [Moench] Voss) seeds, zygotic embryos and megagametophyt es by high performance liquid chromatography and gas chromatography-se lected ion monitoring-mass spectrometry. In seeds, the ABA content was high at the early embryo developmental stage and underwent a further rapid increase at the precotyledonary stage about 4 weeks after pollin ation (AFP), This latter increase in ABA corresponded with an increase in seed dry weight 4-6 weeks AFP. Increases of ABA continued until th e late maturation stage (8 weeks AFP). The endogenous ABA concentratio n on a dry weight basis was higher in embryos than in megagametophytes , but the total ABA content per structure was lower in embryos than in megagametophytes because the size and weight of these two structures were different. At the late maturation stage, ABA amounts decreased ea rlier in embryos (8 weeks AFP) than in megagametophytes (10 weeks AFP) . Low concentrations of ABA were observed in embryos and megagametophy tes of stored seeds. During development, the endogenous IAA amount in the megagametophytes declined after pollination. This was followed by an increase from 2 to 6 weeks AFP. During late maturation, the IAA con tent increased in megagametophytes but decreased in the embryos. Throu ghout seed development, GA(4) slightly decreased while GA(9) increased . Endogenous GA(7) remained very low throughout. In stored seeds, amou nts of both IAA and GAs were lower than in developing seeds. Concomita nt with a rapid increase in seed dry weight, seed moisture content (MC ) decreased sharply between precotyledonary stage and early cotyledona ry stage (4 and 6 weeks AFP). Seeds could absorb water and germinate a fter a significant decrease of MC and at a high endogenous ABA content (8 weeks AFP). These results suggest that endogenous ABA, IAA and GAs are involved in white spruce embryogenesis. There are relatively high ABA and IAA contents in the embryo environment but the GAs checked in this study are low.