Control of xylem Na(+) loading and transport to the shoot in rice and barley as a determinant of differential salinity stress tolerance.

Control of xylem Na+ loading has often been named as the essential component of salinity tolerance mechanism. However, it is less clear to what extent the difference in this trait may determine differential salinity tolerance between species. In this study, barley (Hordeum vulgare L. cv. CM72) and rice (Oryza sativa L. cv. Dongjin) plants were grown under two levels of salinity. Na+ and K+ concentrations in the xylem sap, and shoot and root tissues were measured at different time points after stress onset. Salt-exposed rice plants prevented xylem Na+ loading for several days, but failed to control this process in the longer term, ultimately resulting in a massive Na+ shoot loading. Barley plants quickly increased xylem Na+ concentration and its delivery to the shoot (most likely for the purpose of osmotic adjustment) but were able to reduce this process later on, keeping most of accumulated Na+ in the root, thus maintaining non-toxic shoot Na+ level. Rice plants increased shoot K+ concentration, while barley plants maintained higher root K+ concentration. Control of xylem Na+ loading is remarkably different between rice and barley; this difference may differentiate the extent of the salinity tolerance between species. This trait should be investigated in more detail to be used in the breeding programs aimed to improve salinity tolerance in crops.

Ishikawa T ，Shabala S 《-》

Kinetics of xylem loading, membrane potential maintenance, and sensitivity of K(+) -permeable channels to reactive oxygen species: physiological traits that differentiate salinity tolerance between pea and barley.

Salt sensitive (pea) and salt tolerant (barley) species were used to understand the physiological basis of differential salinity tolerance in crops. Pea plants were much more efficient in restoring otherwise depolarized membrane potential thereby effectively decreasing K(+) efflux through depolarization-activated outward rectifying potassium channels. At the same time, pea root apex was 10-fold more sensitive to physiologically relevant H2 O2 concentration and accumulated larger amounts of H2 O2 under saline conditions. This resulted in a rapid loss of cell viability in the pea root apex. Barley plants rapidly loaded Na(+) into the xylem; this increase was only transient, and xylem and leaf Na(+) concentration remained at a steady level for weeks. On the contrary, pea plants restricted xylem Na(+) loading during the first few days of treatment but failed to prevent shoot Na(+) elevation in the long term. It is concluded that superior salinity tolerance of barley plants compared with pea is conferred by at least three different mechanisms: (1) efficient control of xylem Na(+) loading; (2) efficient control of H2 O2 accumulation and reduced sensitivity of non-selective cation channels to H2 O2 in the root apex; and (3) higher energy saving efficiency, with less ATP spent to maintain membrane potential under saline conditions.

Bose J ，Shabala L ，Pottosin I ，Zeng F ，Velarde-Buendía AM ，Massart A ，Poschenrieder C ，Hariadi Y ，Shabala S ... -  《-》

Over-expression of an Na+-and K+-permeable HKT transporter in barley improves salt tolerance.

Soil salinity is an increasing menace that affects agriculture across the globe. Plant adaptation to high salt concentrations involves integrated functions, including control of Na+ uptake, translocation and compartmentalization. Na+ transporters belonging to the HKT family have been shown to be involved in tolerance to mild salt stress in glycophytes such as Arabidopsis, wheat and rice by contributing to Na+ exclusion from aerial tissues. Here, we have analysed the role of the HKT transporter HKT2;1, which is permeable to K+ and Na+, in barley, a relatively salt-tolerant crop that displays a salt-including behaviour. In Xenopus oocytes, HvHKT2;1 co-transports Na+ and K+ over a large range of concentrations, displaying low affinity for Na+, variable affinity for K+ depending on external Na+ concentration, and inhibition by K+ (K(i) approximately 5 mm). HvHKT2;1 is predominantly expressed in the root cortex. Transcript levels are up-regulated in both roots and shoots by low K+ growth conditions, and in shoots by high Na+ growth conditions. Over-expression of HvHKT2;1 led to enhanced Na+ uptake, higher Na+ concentrations in the xylem sap, and enhanced translocation of Na+ to leaves when plants were grown in the presence of 50 or 100 mm NaCl. Interestingly, these responses were correlated with increased barley salt tolerance. This suggests that one of the factors that limits barley salt tolerance is the capacity to translocate Na+ to the shoot rather than accumulation or compartmentalization of this cation in leaf tissues. Thus, over-expression of HvHKT2;1 leads to increased salt tolerance by reinforcing the salt-including behaviour of barley.

Mian A ，Oomen RJ ，Isayenkov S ，Sentenac H ，Maathuis FJ ，Véry AA ... -  《-》

Regulation of cation transporter genes by the arbuscular mycorrhizal symbiosis in rice plants subjected to salinity suggests improved salt tolerance due to reduced Na(+) root-to-shoot distribution.

Porcel R ，Aroca R ，Azcon R ，Ruiz-Lozano JM ... -  《-》

Changes in Expression Level of OsHKT1;5 Alters Activity of Membrane Transporters Involved in K(+) and Ca(2+) Acquisition and Homeostasis in Salinized Rice Roots.

Al Nayef M ，Solis C ，Shabala L ，Ogura T ，Chen Z ，Bose J ，Maathuis FJM ，Venkataraman G ，Tanoi K ，Yu M ，Zhou M ，Horie T ，Shabala S ... -  《INTERNATIONAL JOURNAL OF MOLECULAR SCIENCES》