RELATIONSHIP BETWEEN WATERCORE AND MEMBRANE-PERMEABILITY IN THE JAPANESE PEAR (PYRUS-PYRIFOLIA NAKAI CV HOSUI)

The development of watercore in fruits of potted trees of the Japanese pear (Pyrus pyrifolia Nakai cv. Hosui) in relation to a change in the membrane permeability as influenced by diurnal temperatures was investigated. The levels of K+ efflux through the membranes of fruits with watercore were compared with fruits without the watercore symptoms. 1. The optimal condition for measuring the K+ efflux through the membrane of flesh samples was to shake the tissues in 0.3 M or 0.5 M glycerin solution at 25-degrees-C. The concentration of Ca2+ in the shaking solutions had no relation to K efflux. 2. Tissue samples from fruits with watercore leaked K+ faster than did those without watercore. 3. When the ground color at the calyx end of fruits reached level 2 or 4, the membranes of fruits exposed to 23-degrees/15-degrees-C (day/night) in July were found to be more permeable than were those from fruits on trees which had been exposed to 33-degrees/25-degrees-C or were continuously field-grown (control trees) . Furthermore, the membrane permeability of fruits, exposed to relatively low summer diurnal temperatures, began at an earlier stage of fruit development than did that from the control fruits. 4. In those years during which there were more cool summer days, the membrane was more permeable in 'Hosui' fruits than it was in fruits which matured in warmer summer temperatures. 5. When fruits were treated with ethephon and GA, K+ efflux was accelerated and occurred earlier than they did in control fruits.