SALT TOLERANCE OF RICE CULTIVARS IN GREENHOUSE

Abstract: The response of 10 rice cultivars, including the salt-tolerant variety (Pokkali) and salt-susceptible variety (IR29) as controls at five salinity levels (i.e., 0, 4, 6, 8, and 10 dS·m–1) under hydroponic conditions was studied at the seedling stage in the greenhouse. The heading stage was evaluated at the salinity level of 8 dS·m–1 in a completely randomized block with 3 replications per each cultivar under non-saline and saline conditions. The results show that the growth of cultivars is retarded severely at the external salinity levels. Almost all leaves dried and died completely (score 7 and 9) at the level of 8 to 10 dS·m–1. Cultivars IR29 and OM7347 died (score 9) at 10 dS·m–1; whereas, Pokkali and IR93350 were evaluated at score 5. Salinity induces the reduction of overall agronomic parameters of cultivars, especially in dry weight relative-to-reduction over control (ROC%), salt tolerance index (STI%), pollen germination, and grain yield. Salinity-sensitive cultivars decreased their pollen viability by more than 50%, leading to a poor grain yield at a salt level of 8 dS·m–1. Tested cultivars as an initial response to salinity stress were ranked as follows: OM7347, IR87832-303-1-B, and IR29 – susceptible; OM8104, IR93340, and IR93343 – moderately tolerant, and IR86385-8D-1-2-B, IR5040, IR93350, and Pokkali – tolerant.Keywords: heading stage, pollen germination, susceptible, seedling stage, salinity-toleran

Identification and Characterization of Rice OsHKT1;3 Variants

In rice, the high-affinity K+ transporter, OsHKT1;3, functions as a Na+-selective transporter. mRNA variants of OsHKT1;3 have been reported previously, but their functions remain unknown. In this study, five OsHKT1;3 variants (V1-V5) were identified from japonica rice (Nipponbare) in addition to OsHKT1;3_FL. Absolute quantification qPCR analyses revealed that the transcript level of OsHKT1;3_FL was significantly higher than other variants in both the roots and shoots. Expression levels of OsHKT1;3_FL, and some variants, increased after 24 h of salt stress. Two electrode voltage clamp experiments in a heterologous expression system using Xenopus laevis oocytes revealed that oocytes expressing OsHKT1;3_FL and all of its variants exhibited smaller Na+ currents. The presented data, together with previous data, provide insights to understanding how OsHKT family members are involved in the mechanisms of ion homeostasis and salt tolerance in rice.</p

A Survey of Barley PIP Aquaporin Ionic Conductance Reveals Ca2+-Sensitive HvPIP2;8 Na+ and K+ Conductance

Some plasma membrane intrinsic protein (PIP) aquaporins can facilitate ion transport. Here we report that one of the 12 barley PIPs (PIP1 and PIP2) tested, HvPIP2;8, facilitated cation transport when expressed in Xenopus laevis oocytes. HvPIP2;8-associated ion currents were detected with Na+ and K+, but not Cs+, Rb+, or Li+, and was inhibited by Ba2+, Ca2+, and Cd2+ and to a lesser extent Mg2+, which also interacted with Ca2+. Currents were reduced in the presence of K+, Cs+, Rb+, or Li+ relative to Na+ alone. Five HvPIP1 isoforms co-expressed with HvPIP2;8 inhibited the ion conductance relative to HvPIP2;8 alone but HvPIP1;3 and HvPIP1;4 with HvPIP2;8 maintained the ion conductance at a lower level. HvPIP2;8 water permeability was similar to that of a C-terminal phosphorylation mimic mutant HvPIP2;8 S285D, but HvPIP2;8 S285D showed a negative linear correlation between water permeability and ion conductance that was modified by a kinase inhibitor treatment. HvPIP2;8 transcript abundance increased in barley shoot tissues following salt treatments in a salt-tolerant cultivar Haruna-Nijo, but not in salt-sensitive I743. There is potential for HvPIP2;8 to be involved in barley salt-stress responses, and HvPIP2;8 could facilitate both water and Na+/K+ transport activity, depending on the phosphorylation status