DEVELOPMENT OF H+ EXTRUSION BY BARLEY ROOTS AFTER THEIR EXCISION

Net H+ transport by barley (H. vulgare) roots was measured with a pH-stat system. In absence of antibiotics the apparent H+ efflux quickly decreased after excision of the roots and gave place to an apparent H+ influx. This alcalinization, which was prevented by adding antibiotics to the medium, probably resulted from microbial decarboxylation of carboxylates transported into the medium via the xylem. Apart from allowing carboxylates to be released into the medium, excision had 2 main effects on H+ transport. The 1st was inhibition due to the injury shock which did not extend far from the wounded tissues. The 2nd was a decrease of the pumping rate, which could be delayed by adding glucose to the medium, which prevented a decline in tissue glucose. These results are relevant to the classical protocols for studying the H+ pump in roots.