トマトにおける果実生長および光合成産物の転流の動態に対する環境作用 （第２報） 師管液および道管液フラックスと果実水収支の解析

Abstract

Water balance in a growing fruit of tomato (Lycopersicon esculentum Mill.) as affected by irradiance and air temperature was analyzed with special reference to phloem and xylem transport. Separate evaluations of phloem sap and xylem sap fluxes through the pedicel were enabled by the cooperative application of the multiple chamber system for measuring rates of expansive growth and gas exchange in the fruits and the heat-ring method for inhibiting phloem transport through the pedicel. A little more than 80% of sap flux through the pedicel contributed to fruit expansive growth, and the residual (i.e. a little less than 20%) was lost by transpiration from the fruit with calyx and pedicel. The most dominant component of fruit water balance was phloem sap flux, and about 70% of sap accumulated into the fruit was brought by phloem transport, which was significantly accelerated with leaf photosynthesis and fruit respiration activated by lighting and rise in air temperature after the start of the light period. Xylem sap flux found to be a minor component in fruit water balance and less sensitive to the temperature rise as compared with phloem sap flux. Thus, the separate evaluations of phloem sap and xylem sap fluxes through a pedicel can be considered to give useful information on mass accumulation into tomato fruits.