Mechanisms of fruit cell expansion with intact water potential measurements

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Water potential measurements are usually conducted with the psychrometry by using excised tissues. When tissues are growing, and then, if excision is made in the zone of elongation for sampling, it is known that wall relaxation will take place. If wall relaxation due to excision takes place in the zone of elongation, water potential measurements with the psychrometer may not be accurately conducted because wall relaxation will make the measured value of water potential shift lower. However, the psychrometry is only a method which allows to measure the water potential in intact plants. Thus, improvement of the psychrometry is helpful for measuring water potential in intact plants. In order to improve the psychrometry, the output of a psychrometer was attempted to multiply by 3 times by malting a thermopile for the sensor of the psychrometer. The thermopile was made by combining 3 thermocouple junctions. Output of one thermocouple yields 480 nV per 0.1 MPa. Although the thermopile made in the present study should yield 3 times of 480 nV per 0.1 MPa, the output of the thermopile yielded only 2.0 to 2.4 times of that of one thermocouple. This failure might be due to connection between the thermocouples by using solder. The process of soldering between the thermocouples may yield the extra noise to reduce the thermocouple output. The water status of intact tomato fruit and endosperm cells of rice plants was measured with the pressure probe and psychrometers. Cell expansion in both plants was associated with the gradient of the growth-induced water potential High night temperature reduced the water potential gradient in endosperm cells of rice, resulting in yield decrease of rice at high temperature.