Arbuscular mycorrhizal symbioses alleviating salt stress in maize is associated with a decline in root-to-leaf gradient of Na(+)/K(+) ratio.

Inoculation of arbuscular mycorrhizal (AM) fungi has the potential to alleviate salt stress in host plants through the mitigation of ionic imbalance. However, inoculation effects vary, and the underlying mechanisms remain unclear. Two maize genotypes (JD52, salt-tolerant with large root system, and FSY1, salt-sensitive with small root system) inoculated with or without AM fungus Funneliformis mosseae were grown in pots containing soil amended with 0 or 100 mM NaCl (incrementally added 32 days after sowing, DAS) in a greenhouse. Plants were assessed 59 DAS for plant growth, tissue Na+ and K+ contents, the expression of plant transporter genes responsible for Na+ and/or K+ uptake, translocation or compartmentation, and chloroplast ultrastructure alterations. Under 100 mM NaCl, AM plants of both genotypes grew better with denser root systems than non-AM plants. Relative to non-AM plants, the accumulation of Na+ and K+ was decreased in AM plant shoots but increased in AM roots with a decrease in the shoot: root Na+ ratio particularly in FSY1, accompanied by differential regulation of ion transporter genes (i.e., ZmSOS1, ZmHKT1, and ZmNHX). This induced a relatively higher Na+ efflux (recirculating) rate than K+ in AM shoots while the converse outcoming (higher Na+ influx rate than K+) in AM roots. The higher K+: Na+ ratio in AM shoots contributed to the maintenance of structural and functional integrity of chloroplasts in mesophyll cells. AM symbiosis improved maize salt tolerance by accelerating Na+ shoot-to-root translocation rate and mediating Na+/K+ distribution between shoots and roots.

Wang H ，An T ，Huang D ，Liu R ，Xu B ，Zhang S ，Deng X ，Siddique KHM ，Chen Y ... -  《BMC PLANT BIOLOGY》

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 ... -  《-》

Effect of arbuscular mycorrhizal symbiosis on ion homeostasis and salt tolerance-related gene expression in halophyte Suaeda salsa under salt treatments.

Halophytes can remove large quantities of salts from saline soils, so their importance in ecology has received increasing attention. Preliminary studies have shown that arbuscular mycorrhizal (AM) fungi can improve the salt tolerance of halophytes. However, few studies have focused on the molecular mechanisms and effects of AM fungi in halophytes under different salt conditions. A pot experiment was carried out to investigate the effects of Funneliformis mosseae inoculation on growth, nutrient uptake, ion homeostasis and the expression of salt tolerance-related genes in Suaeda salsa under 0, 100, 200 and 400 mM NaCl. The results showed that F. mosseae promoted the growth of S. salsa and increased the shoot Ca2+ and Mg2+ concentrations under no-salt condition and high-salt condition. In addition, AM fungi increased the K+ concentration and maintained a high K+/Na+ ratio at 400 mM NaCl, while AM fungi decreased the K+ concentration and reduced the K+/Na+ ratio at 0 mM NaCl. AM fungi downregulated the expression of SsNHX1 in shoots and the expression of SsSOS1 in roots at 400 mM NaCl. These effects may decrease the compartmentation of Na+ into leaf vacuoles and restrict Na+ transport from roots to shoots, leading to an increase in root Na+ concentration. AM symbiosis upregulated the expression of SsSOS1 in shoots and downregulated the expression of SsSOS1 and SsNHX1 in roots at 100 mM NaCl. However, regulation of the genes (SsNHX1, SsSOS, SsVHA-B and SsPIP) was not significantly different with AM symbiosis at 0 mM or 200 mM NaCl. The results revealed that AM symbiosis might induce diverse modulation strategies in S. salsa, depending on external Na+ concentrations. These findings suggest that AM fungi may play significant ecological roles in the phytoremediation of salinized ecosystems.

Diao F ，Dang Z ，Xu J ，Ding S ，Hao B ，Zhang Z ，Zhang J ，Wang L ，Guo W ... -  《-》

Spore associated bacteria regulates maize root K(+)/Na(+) ion homeostasis to promote salinity tolerance during arbuscular mycorrhizal symbiosis.

Selvakumar G ，Shagol CC ，Kim K ，Han S ，Sa T ... -  《BMC PLANT BIOLOGY》

Arbuscular mycorrhizal fungi native from a Mediterranean saline area enhance maize tolerance to salinity through improved ion homeostasis.

Soil salinity restricts plant growth and productivity. Na(+) represents the major ion causing toxicity because it competes with K(+) for binding sites at the plasma membrane. Inoculation with arbuscular mycorrhizal fungi (AMF) can alleviate salt stress in the host plant through several mechanisms. These may include ion selection during the fungal uptake of nutrients from the soil or during transfer to the host plant. AM benefits could be enhanced when native AMF isolates are used. Thus, we investigated whether native AMF isolated from an area with problems of salinity and desertification can help maize plants to overcome the negative effects of salinity stress better than non-AM plants or plants inoculated with non-native AMF. Results showed that plants inoculated with two out the three native AMF had the highest shoot dry biomass at all salinity levels. Plants inoculated with the three native AMF showed significant increase of K(+) and reduced Na(+) accumulation as compared to non-mycorrhizal plants, concomitantly with higher K(+) /Na(+) ratios in their tissues. For the first time, these effects have been correlated with regulation of ZmAKT2, ZmSOS1 and ZmSKOR genes expression in the roots of maize, contributing to K(+) and Na(+) homeostasis in plants colonized by native AMF.

Estrada B ，Aroca R ，Maathuis FJ ，Barea JM ，Ruiz-Lozano JM ... -  《-》