Changes of endogenous hormone levels in developing seeds, zygotic embryos and megagametophytes in Picea glauca

Abstract

Endogenous free abscisic acid (ABA), indole‐3‐acetic acid (IAA) and gibberellins (GAs) were identified and quantified in whole white spruce (Picea glauca [Moench] Voss) seeds, zygotic embryos and megagametophytes by high performance liquid chromatography and gas chromatography‐selected 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 pollination (AFP). This latter increase in ABA corresponded with an increase in seed dry weight 4–6 weeks AFP. Increases of ABA continued until the late maturation stage (8 weeks AFP). The endogenous ABA concentration 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 earlier in embryos (8 weeks AFP) than in megagametophytes (10 weeks AFP). Low concentrations of ABA were observed in embryos and megagametophytes 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 content increased in megagametophytes but decreased in the embryos. Throughout seed development, GA4 slightly decreased while GA9 increased. Endogenous GA7 remained very low throughout. In stored seeds, amounts of both IAA and GAs were lower than in developing seeds. Concomitant with a rapid increase in seed dry weight, seed moisture content (MC) decreased sharply between precotyledonary stage and early cotyledonary stage (4 and 6 weeks AFP). Seeds could absorb water and germinate after 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.