EMBRYO WATER STATUS AND SURVIVAL IN THE RECALCITRANT SPECIES QUERCUS-ROBUR L - EVIDENCE FOR A CRITICAL MOISTURE-CONTENT

The responses of Q. robur L. fruits, seeds and embryonic axes to desiccation are characterized and discussed in relation to current knowledge of recalcitrant seed behaviour. A relationship between viability and seed moisture content is described. This relationship was unaffected by rate of drying, year of harvest or presence of the pericarp. Desiccation sensitivity did not increase with storage. Excised embryonic axes survived to lower moisture contents than intact seeds. However, in the intact seed, loss of viability appeared to be determined by a critical moisture content in the cotyledons. Consequently, the level of desiccation tolerance within the axis attached to cotyledons was not determined by axis drying rate. A link is drawn between the difference in the desiccation tolerance of embryonic axes and of cotyledons, and estimates of their different levels of matrix-bound water. The results presented are consistent with a critical moisture content for survival which is determined by the loss of all free cellular water. This hypothesis takes account of the differential desiccation sensitivity of seed tissues and differences in desiccation tolerance between species.