Effect of Salinity on Respiratory Pathways in Root Tips of Tamarix tetragyna

Oxygen uptake in the presence of exogenous glucose was lower in Tamarix root tips grown in saline media than in those grown in Hoagland solution. This effect was not overcome by raising the external glucose concentration.Glucose uptake and CO(2) evolution were depressed in the presence of NaCl. This effect was observed also when roots were exposed to salinity only during growth but not during uptake. Increasing the external concentration of glucose from 0.01 to 1 mm induced only a 10-fold increase in glucose uptake and CO(2) evolution. However, (14)C evolved in CO(2) as percent of (14)C absorbed, remained constant at all salinity treatments, and was similar at both glucose concentrations.Salinity above 120 mm NaCl increased the percentage of absorbed glucose oxidized via the pentose phosphate pathway, but did not affect the glycolytic pathway. At the same time, salinity depressed the glucose-6-P dehydrogenase, pyruvate kinase, and oxidative phosphorylation. These effects become most evident at a salinity level of about - 10 atm (240 mm), a concentration which is rarely exceeded in the root zone of the natural habitat of the plants.We concluded that Tamarix is reasonably well adapted to the conditions of its habitat, and that salinity affects its root metabolism differently than it does that of pea roots.