WATER PERMEABILITY CHANGES OF THE CELL MEMBRANE AS A FUNCTION OF TIME

Water loss and microscopic water migration inside tissues or cells are major causes of vegetable deterioration and wilting during the postharvest period.
Water loss and water migration caused by respiration and transpiration are influenced by the condition of the cell membrane or other biomembranes.
Therefore, for the studying on postharvest technology, it is essential to understand the changes in the properties of biomembranes of the agricultural products during the storage.
The change in cell membrane water permeability coefficient (L_p) and osmotic tolerance of barley cotyledon protoplast was measured and the change in dynamic state of water in the cotyledons was estimated by 1H-NMR during the storage.
The barley cotyledons were cut from the plants and stored in test tubes at 20°C in dark.
The storage periods were 0, 24, 48 and 72 hours.
After the storage, protoplasts were separated from the cotyledons and the L_p of the cell membranes were measured by Two Laminar Flow (TLF) Method.
In the TLF Method, the L_p was determined from volume change ratio of the protoplast under the osmotic stress.
The L_p decreased after the 24 hours storage, however, it increased afterward.
It was supposed that decline in functional activities or decrease in amount of the water channels in the cell membrane induced the initial decrease of the L_p. And deterioration of phospholipids bilayer composing the cell membrane caused the successive increase of the L_p.
The osmotic tolerance of the protoplasts continued to decrease throughout the storage period and existences of two processes in the decline were suggested from the time-dependent change in variance of the osmotic tolerance.
Because water leakage from vacuole to cytoplasm was detected by the NMR measurements, the osmotic tolerance decline was thought to be divided into two different processed; the first one was the process caused by the deterioration of the tonoplast and second one was the process caused by the deterioration of the cell membrane after the tonoplast deterioration.

V International Postharvest Symposium

I. Sotome, J. De Baerdemaeker, S. Oshita, Y. Kawagoe

aquaporins, barley, NMR, phospholipids bilayer, protoplast, Two Laminar Flow method, water channel

https://doi.org/10.17660/ActaHortic.2005.682.147