THE FREE-SPACE OF SUGARS IN PLANT-TISSUES - EXTERNAL FILM AND APOPLASTIC VOLUME

The total volume of the free space (FS) and the external film (EF) out side the cell wall of living plant materials was determined as partiti on volumes of sugars and dextran, respectively. Sugar uptake and kinet ics of FS and EF saturation were recorded polarimetrically. The FS equ ilibrates within 20 s in suspension culture of Chenopodium album L. He re, the free apoplastic volume (FAV), i.e. the difference between suga r and dextran partition volumes, was determined by shortterm partition ing of fructose and dextran in samples containing the plant material a nd an optically compensated (non-rotating) solution of both components . The selective partitioning of the sugar with the FAV causes an incre ase in optical activity, which is dependent on the FAV. The FAV of a s uspension cultured biomass was found to be correlated with the percent age volume of dead cells. The volume originating by plasmolysis betwee n cell wall and plasma membrane was measured as an increase of the FAV . In seedling root segments of Zea mays L., the component of FS equili brating within 1 min consisted of the EF and a portion of the FAV (pro bably dead cells at the surface). Saturation of the apoplast of the in filtrated root cortex with alpha-methylglucoside, a sugar not taken up by the cells, showed slow equilibration kinetics and was not complete within 30 min.