K ⁺ and Na ⁺ fluxes in roots of two Chinese Iris populations

Abstract

Maintenance of ion homeostasis, particularly the regulation of K ⁺ and Na ⁺ uptake, is important for all plants to adapt to salinity. Observations on ionic response to salinity and net fluxes of K ⁺, Na ⁺ in the root exhibited by plants during salt stress have highlighted the need for further investigation. The objectives of this study were to compare salt adaptation of two Chinese Iris ( Iris lactea Pall. var. chinensis (Fisch.) Koidz.) populations, and to improve understanding of adaptation to salinity exhibited by plants. Plants used in this study were grown from seeds collected in the Xinjiang Uygur Autonomous Region (Xj) and Beijing Municipality (Bj), China. Hydroponically-grown seedlings of the two populations were supplied with nutrient solutions containing 0.1 (control) and 140 mmol·L ^-1 NaCl. After 12 days, plants were harvested for determination of relative growth rate and K ⁺, Na ⁺ concentrations. Net fluxes of K ⁺, Na ⁺ from the apex and along the root axis to 10.8 mm were measured using non-invasive micro-test technique. With 140 mmol·L ^-1 NaCl treatment, shoots for population Xj had larger relative growth rate and higher K ⁺ concentration than shoots for population Bj. However, the Na ⁺ concentrations in both shoots and roots were lower for Xj than those for Bj. There was a lower net efflux of K ⁺ found in population Xj than by Bj in the mature zone (approximately 2.4-10.8 mm from root tip). However, no difference in the efflux of Na ⁺ between the populations was obtained. Population Xj of I. lactea continued to grow normally under NaCl stress, and maintained a higher K ⁺/Na ⁺ ratio in the shoots. These traits, which were associated with lower K ⁺ leakage, help population Xj adapt to saline environments.