The free space of sugars in plant tissues6

Abstract

The total volume of the free space (FS) and the external film (EF) outside the cell wall of living plant materials was determined as partition volumes of sugars and dextran, respectively. Sugar uptake and kinetics of FS and EF saturation were recorded polarimetrically. The FS equilibrates within 20 s in suspension culture of Chenopodium album L. Here, the free apoplastic volume (FAV), i.e. the difference between sugar and dextran partition volumes, was determined by shortterm partitioning of fructose and dextran in samples containing the plant material and an optically compensated (non-rotating) solution of both components. The selective partitioning of the sugar with the FAV causes an increase in optical activity, which is dependent on the FAV. The FAV of a suspension cultured biomass was found to be correlated with the percentage volume of dead cells. The volume originating by plasmolysis between 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 equilibrating within 1 min consisted of the EF and a portion of the FAV (probably dead cells at the surface). Saturation of the apoplast of the infiltrated root cortex with α-methylglucoside, a sugar not taken up by the cells, showed slow equilibration kinetics and was not complete within 30 min.