Amino Acids Translocated from Turgid and Water-stressed Barley Leaves

Abstract

Movement of labeled amino acids from leaf blades to sheaths was followed after supplying (13)NH(3) gas, (14)CO(2), or (14)C-amino-acids to attached blades of barley plants.Blades of turgid and wilted plants fed (13)NH(3) (at about 120 to 700 microliters per liter) had incorporated (13)N mainly into free glutamine and glutamate after 30 minutes, and turgid blades had exported 1 to 3% of the assimilated (13)N to the sheaths, mostly as glutamine and glutamate. Wilted blades exported less of the assimilated (13)N than turgid blades even though they exported (14)CO(2) assimilates as actively as turgid blades.When substrate amounts (about 0.28 micromole) of [(14)C]glutamate and [(14)C]proline were applied to turgid and wilted blades, these amino acids entered the phloem and were translocated at velocities similar to those for (14)CO(2) assimilates (about 0.2 centimeter per minute). Wilted blades metabolized tracer amounts of [(14)C]glutamate to glutamine and proline, and exported (14)C in the form of these three amino acids. Approximate calculations of mass transfer rates of glutamate, glutamine, and proline made for wilted blades indicated that glutamine and glutamate together carried 76 micrograms of N per day, whereas proline carried only about 9 micrograms of N per day.