Study on the mechanism of quality deterioration of agricultural products through cell membrane permeability and surface nature of cell wall

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As indices of water permeability of spinach leaf cells, 2 kinds of water permeability coefficient, diffusional permeability Pd and osmotic permeability Lp were measured and the change in expression of aquaporin PM28A that regulates water movement across membrane with time was also examined.Through the measurement of Pd by NMR method, the water exchange time and diffusional water permeability were determined at the end of 1d and 6d storage under 2℃, The results showed that the water exchange time and the diffusional water permeability varied from 71.3 ms to 55.4 ms and from 5.1x10^<-5> to 6.6x10^<-5> ms^<-1> respectively. This indicated the increase in water permeability of cell membrane as storage time quantitatively.The osmotic water permeability Lp was also measured by newly developed method that makes a protoplast expose to solutions with different osmotic pressure. Lp was determined for the spinach leaf cells stored at 2℃ and 20℃. While Lp increased after at least 72h storage at 20℃, it was kept almost same as the initial value. The increase in Lp is caused by the increase in the expression of aquaporin that accelerates the water transport and/or the change in membrane properties due to loose packing of phospholipid bilayer. As the expression of PM28A, one of aquaporins, measured in this study decreased to nearly half in 2d storage, the deterioration of phospholipid bilayer is considered to be a major cause of the increase in Lp after 72h storage.With the information above, this study gives the clue to suppress water loss in 1 to 2 d after harvest by applying an appropriate stress to agricultural products to decrease the expression of aquaporin.