MICROSPECTROPHOTOMETRIC INVESTIGATIONS OF FREE SPACE IN PLANT CELL WALLS

Two equations were proposed for the determination of free space in plant cell walls. Solution of the equations required microspectrophotometric measurements of cell walls after introduction of a chromophore. A periodic acid-Schiff test was developed for this purpose and a statistical analysis of the error terms was used to evaluate the discriminatory capacity of the system. Bouguer's law was tested directly and found to hold for the tissue thicknesses and wavelengths used. Because concentration was unknown, Beer's law could not be tested directly, but a new method based on the logarithmic transformation of the optical densities and statistical correlation of curve shape was used to predict the wavelength interval in which Beer's law held. Calculations by a newly derived extinction-ratio equation (AE/E) were essentially invariant over the predicted range and variable outside of this wavelength interval. Free space in hydrated S₂ layers of tracheid cell walls of Pinus resinosa Ait. was calculated to be about 25%. The magnitude of free space at various stages of hydration was also tabulated. Considerable free space was found to exist in plant cell walls after prolonged exposure to anhydrous ethyl alcohol; however, after complete dehydration there was little evidence of residual free space.