Seed Development in the Recalcitrant Species<i>Quercus robur</i>L: Water Status and Endogenous Abscisic Acid Levels

Abstract

Water status and endogenous ABA levels were measured during the development of the embryonic axis and cotyledons in fruits of Quercus robur L. As dry matter accumulated in the embryo during development, both moisture content and osmotic potential (ψ,) declined. Measured by combined gas chromatography-mass spectrometry, ABA concentration in the axis remained high until near shedding, when it declined. In the cotyledons there was a well-defined, transient peak in ABA concentration coinciding with the start of their rapid increase in starch content. At shedding, the cotyledons had a lower moisture content and lower ψ, than the axis. After shedding, axis dry weight increased and moisture content declined in storage, suggesting a late continuation of development. Prematurely harvested fruits, stored in the absence of water, also showed continued axis development, and subsequently germinated without prior desiccation. There was no evidence of post-maturation drying in the embryo, although there was a small net loss of water from the cotyledons before shedding. Embryo development in Q. robur, therefore, differed significantly from that in orthodox seeds of other dicotyledonous species.