MATRIC POTENTIAL EVALUATIONS AND MEASUREMENTS FOR GELLED SUBSTRATES

A new method for evaluating the matric potential of gelled media has b een developed. The method allows the derivation of the matric potentia l as a limit of a series of measurements of water potential values fro m gelled media prepared without added components, from agar powders pr ogressively cleaned of mineral impurities. Three commercial agar brand s were tested, and for these the matric potential was found to contrib ute only between 1 and 2% of their total water potential. Thermodynami c features relating matric and osmotic potentials are described. New h ypotheses for understanding the water flux mechanism from gel to tissu e cultured explants are discussed. Movement of water along polymeric c hains is postulated to be a facilitated step in comparison with bulk m ovement.