SEED COAT CELL TURGOR RESPONDS RAPIDLY TO AIR HUMIDITY IN CHICKPEA AND FABA-BEAN

The turgor pressure in cells of chickpea (Cicer arietinum L.) and faba bean (Vicia faba L.) seed coats was measured with a pressure probe. M easurements were made under in situ conditions by removing a section o f wall from a pod, which remained attached to the plant, and exposing the intact seed. If the pod wall was removed and the turgor measuremen ts made under ambient laboratory conditions of 50% to 70% relative hum idity (RH), cell turgor pressure declined over time, typically reachin g 0 MPa. If the pod wail was removed and the turgor measurements made under conditions of 100% RH, however, cell turgor pressure was stable over time, relatively uniform within the seed coat tissue, and was fou nd to be 0.1-0.3 MPa for chickpea, and 0.1-0.2 MPa for faba bean. In b oth species there was a marked decline in cell turgor, beginning withi n about 60 s, when humidification was discontinued. The decline in cel l turgor occurred regardless of the depth of the cell within the seed coat tissue, and this decline could be stopped, but not entirely rever sed, when humidification was restored. An increase in cell turgor coul d also be caused by wetting of the seed. These responses indicate that a very rapid water exchange can occur within the seed coat tissue in situ. The rapid and, in some cases, relatively permanent loss of seed coat cell turgor in the absence of humidification raises serious conce rns regarding desiccation artefacts which may be involved in the empty seed coat technique, often used to study seed carbon and water relati ons in grain legumes.