Osmotic adjustment and ion balance traits of an alkali resistant halophyte Kochia sieversiana during adaptation to salt and alkali conditions

Abstract

Kochia sieversiana (Pall.) C. A. M., a naturally alkali-resistant halophyte, was chosen as the test organism for our research. The seedlings of K. sieversiana were treated with varying (0-400 mM) salt stress (1:1 molar ratio of NaCl to Na 2 SO 4 ) and alkali stress (1:1 molar ratio of NaHCO 3 to Na 2 CO 3 ). The concentrations of various solutes in fresh shoots, including Na + , K + , Ca 2+ , Mg 2+ , Cl À , SO 4 2À , NO 3 À , H 2 PO 3 À , betaine, proline, soluble sugar (SS), and organic acid (OA), were determined. The water content (WC) of the shoots was calculated and the OA components were analyzed. Finally, the osmotic adjustment and ion balance traits in the shoots of K. sieversiana were explored. The results showed that the WC of K. sieversiana remained higher than 6 [g g À1 Dry weight (DW)] even under the highest salt or alkali stress. At salinity levels >240 mM, proline concentrations increased dramatically, with rising salinity. We proposed that this was not a simple response to osmotic stress. The concentrations of Na + and K + all increased with increasing salinity, which implies that there was no competitive inhibition for absorption of either in K. sieversiana. Based on our results, the osmotic adjustment feature of salt stress was similar to that of alkali stress in the shoots of K. sieversiana. The shared essential features were that the shoots maintained a state of high WC, OA, Na + , K + and other inorganic ions, accumulated largely in the vacuoles, and betaine, accumulated in cytoplasm.On the other hand, the ionic balance mechanisms under both stresses were different. Under salt stress, K. sieversiana accumulated OA and inorganic ions to maintain the intracellular ionic equilibrium, with close to equal contributions of OA and inorganic ions to anion. However, under alkali stress, OA was the dominant factor in maintaining ionic equilibrium. The contribution of OA to anion was as high as 84.2%, and the contribution of inorganic anions to anion was only 15.8%. We found that the physiological responses of K. sieversiana to salt and alkali stresses were unique, and that mechanisms existed in it that were different from other naturally alkaliresistant gramineous plants, such as Aneurolepidium chinense, Puccinellia tenuiflora.

Effect of salinity and sodicity stresses on physiological response and productivity inHelianthus annuus

“…Previous studies have shown that the lower level of lipid peroxidation in roots of two rice genotypes may be a response for protection against oxidative damage under salt stress [5]. The application of higher concentration of NaCl or Na 2 CO 3 led to increase the EC rate in sunflower plant, this trend is consistent with previous study [37]. Moreover, supplement of NaCl or Na 2 CO 3 increased the leakage of UV metabolites from leaves.…”

Effect of increased alkalinity on Na⁺ and K⁺ contents, lipid peroxidation and antioxidative enzymes in two populations of Populus cathayana

“…To date, there are only a few reports about alkali stress, especially in trees. Based on previous studies, it is evident that the effects of alkali stress are more severe than those of salt stress (Hartung et al 2002, Shi and Sheng 2005, Yang et al 2007. As there are increasing areas of saline and alkaline soil in the world, it is necessary to do more research on salt-alkali stress and its effects on plants.…”

Effects of salt stress and nitrogen application on growth and ion accumulation of Suaeda salsa plants

“…However, in MS and HS treatments, although nitrogen treatment increased the biomass of leaf, shoot and root, there were no significant differences between LN and MN treatments. Generally, plants can reduce water content as a quick and economical approach to osmotic adjustment in response to osmotic stress [20,21] . Unexpectedly, the LWC in all salt treatments were higher than control (Fig.…”

“…Being a succulent plant, maintaining high LWC can make vacuoles enlarging, which cause the cell surface to increase and make the layer of protoplasm thinner. Cell surface area and the distance between plasmalemma and vacuole membranes are key factors in deciding the speed and power of consumption of inorganic ions and organic small molecules going in and out of each cell [21] . So this might be one of the main physiological characteristics of S. salsa that allow it to have strong resistance to salt stress.…”

“…This phenomenon could be explained that cations were more sensitive to high salt stress than nitrogen treatments. Under salt stress, plants accumulate cations such as Na + and K + [22] , and simultaneously accumulate inorganic anions such as Cl [21] , NO 3 and SO 4 2 [27] to keep ion balance. In this study, the content of Cl and NO 3 increased in salt treatments compared with control, and for the anions balance, SO 4 2 decreased as the increasing of salt stress.…”