Regulation of Amino Acid Uptake into Oat Mesophyll Cells: A Comparison between Protoplasts and Leaf Segments

The uptake of -aminoisobutyric acid (AIB) into protoplasts andinto 1 cm sections of leaves from 7 d old light-grown oats (Avenasativa L. cv. ‘Garry’) was studied. Both protoplastsand leaf sections with cuticle and epidermis removed accumulatedAIB against a concentration gradient although the rate of uptakeinto protoplasts was one-third to one-sixth that into leaf sections.AIB uptake into both protoplasts and leaf cells in situ wasstimulated by ‘aging,’ and low pH, and inhibitedby osmotic shock, respiratory poisons, and KCl concentrationsabove 1 mM. It was concluded that the rate of uptake of AIBand its accumulation ratio could be accounted for by the energyinherent in the proton-motive force, the proton-motive forcebeing the sum of the pH gradient and potential difference acrossthe plasma membrane. The similarities between oat mesophyllprotoplasts and leaf cells in situ suggest that these protoplastsare suitable material for the study of certain membrane-regulatedevents.     

Relationship between Electrical Resistance and Capacitance of Wood in Progressive Stages of Discoloration and Decay

Electrical resistance and capacitance measurements were madeon woody tissues of several tree species. Each tissue was abovethe fibre-saturation point. Values of capacitance were inverselyproportional to values of resistance in woody tissues in progressivestages of discoloration and decay. With the electrode separationused, clear woody tissues had resistances of 110 to 30 k andcapacitances of 0·002 to 0·110 µF. Resistanceand capacitance measure ments of discoloured tissues were 29to 8 k and 0·005 to 0·040 µF, respectively,and those of decayed tissues were 5 to 1 k and 0·60 to0·110 µF. Either electrical measurement could beused to measure the stages of deterioration in woody tissues.Ground woody tissues, cellulose suspensions, starch suspensions,and wood equivalent solutions of potassium chloride had resistanceand capacitance properties similar to those found in intactwoody tissues. Electrical resistance and capacitance propertiesof woody tissues above the fibre-saturation point appear tobe similar to those of dilute solutions of mobile ions.