Boron Uptake by Excised Barley Roots

Active uptake of boron (B) by excised barley roots is linear with time for at least 1.5 h. Although no evidence was found for accumulation of B against a concentration gradient. this component of B uptake does satisfy other criteria for an active transport process. Transport is inhibited by 0.05 m M 2,4‐dinitrophenol, 0.05 m M azide, 5 m M arsenate and 5 m M dicoumarol. Also, uptake is temperature‐sensitive, being nil at 2°C and maximal at 34 to 38°C. Boron uptake by barley roots increases with time when they are washed in aerated 0.5 m M CaSO 4 solution. A double reciprocal plot of the B uptake data manifests a series of phases separated by sharp transitions or “jumps”, and is compatible with the concept of multiphasic uptake mechanisms. Kinetic constants and transition points for the various phases were calculated accordingly. The fit of these data was compared statistically to three other relevant models, viz , the dual model, the “single + diffusion” model (a Michaelis–Menten term and a diffusion term), and the negative cooperativity model. In each case, the data were better represented by the multiphasic model.