Abstract
This study was conducted to determine the responses to saline-alkaline (SA) stress with regard to nutrient accumulation in two rice varieties having different tolerances to salt-stress. A salinity-tolerant landrace, Pokkali, and a salinity-sensitive variety, PTT1, were exposed to three levels of SA conditions, pH 7.0 (mild), pH 8.0 (moderate), and pH 9.0 (severe), under 50 mM Na stress. The results indicated that Pokkali had comparably greater SA tolerance than PTT1 owing to its higher biomass production. The maintenance of the lower Na/K ratio in Pokkali shoots was achieved by the higher expression of OsHKT1;5 encoding a Na+ transporter in the shoots, OsNHX1 encoding a tonoplast-localized Na+/H+ antiporter in the roots, and OsHAK16 encoding a K+ transporter in the roots under SA conditions. We propose that the high expression of Fe deficiency-responsive genes, OsIRT1, OsIRO2, OsYSL15, OsNAS1, and OsNAS2, in both rice varieties under all SA conditions should contribute to Fe homeostasis in the shoots. In addition, SA treatment increased the concentrations of Ca, Mn, Zn, and Cu in the roots but decreased their concentrations in the shoots of both varieties. Overall, the results indicated that high rhizospheric pH influenced nutrient uptake and translocation from the roots to the shoots in rice.
Highlights
Salt-affected soils, including those affected by a large quantity of Na, are harmful to agricultural crops, such as rice
A Na+/H+ antiporter, SOS1, which is located on the plasma membrane of the roots, eliminates Na flowing into the roots, whose activity is increased under high Na conditions [4,5]
To protect cytoplasmic enzymes from Na damage, Na in the cytoplasm of the roots and shoots is sequestered in vacuoles through the action of a K+/Na+ transporter of the NHX family located on the tonoplast to maintain K/Na homeostasis in the cytoplasm [11,12,13,14]
Summary
Salt-affected soils, including those affected by a large quantity of Na, are harmful to agricultural crops, such as rice. The presence of these minerals leads to the classification of soil as either saline or sodic. These sequential salinity-tolerance mechanisms prevent Na from flowing into the leaf blade where photosynthesis and metabolism occur. Aside from the regulation of Na transport, several genetic loci controlling salinity-tolerance in rice have been identified such as saltol QTL [15,16]
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