Embryo Water Status and Development of the Recalcitrant SpeciesQuercus roburL: Determination of Water Relations Parameters by Pressure-Volume Analysis

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Abstract
The water status and water content of embryos of Quercus robur have been determined during development. Using psychrometers, changes in osmotic potential at full imbibition and the proportion of water at zero reciprocal water potential, R0, were estimated from curves of embryo relative water content and reciprocal water potential. The specific moisture content of embryos decreased during development, with a concomitant increase in the osmotic potential. However, R0 also increased such that, during the last four weeks of development, there was little net change in the content of osmoticum per dry weight. Evidence is presented that starch stored in the cotyledon may be the major site of matrix-bound water, R0. Isolated embryonic axes had a slightly higher osmotic potential than the whole embryo but the R0 was much lower. The differences between whole embryo and axis water relations parameters emphasize the need to take account of R0 when discussing seed water status and survival. The results are considered in relation to current models of seed water status and recalcitrant behaviour.

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