RATES AND PATHWAYS FOR WATER DIFFUSION AND BULK FLOW-THROUGH LEAF TISSUE - A NEW TECHNIQUE FOR AN OLD PROBLEM

Nuclear magnetic resonance was used to measure the relative content of [H-1] nuclei in Acer platanoides leaf discs floating on either sucros e/D2O or concentrated PEG/H2O solutions. Data show that water diffusio n and bulk flow follow different pathways through leaf tissue. Isotope exchange data fit accurately an equation derived for diffusion throug h a homogeneous medium with an average diffusion coefficient of 3.3 x 10(-10) m(2) s(-1). A diffusion model featuring cell wall barriers was shown to be unnecessary. The diffusion rate is too fast to be consist ent with transport solely through apoplastic channels and instead, wat er molecules appear to move directly through contiguous compartments. The discs lost water by osmosis into the PEG solution with an exponent ial decay function, which was shown to be consistent with a fractal mo del of bulk flow. (C) 1997 Elsevier Science Ireland Ltd.