Ionic selectivity and coordinated transport of Na+ and K+ in flag leaves render differential salt tolerance in rice at the reproductive stage
The present study shows that salt tolerance in the reproductive stage of rice is primarily governed by the selective Na+ and K+ transport from the root to upper plant parts. Ionic discrimination at the flag leaf, governed by differential expression of Na+- and K+-specific transporters/ion pumps, is associated with reduced spikelet sterility and reproductive stage salt tolerance.
Reproductive stage salt tolerance is crucial in rice to guarantee yield under saline condition. In the present study, differential ionic selectivity and the coordinated transport (from root to flag leaf) of Na+ and K+ were investigated to assess their impact on reproductive stage salt tolerance. Four rice genotypes having differential salt sensitivity were subjected to reproductive stage salinity stress in pots. The selective Na+ and K+ transport from the root to upper plant parts was observed in tolerant genotypes. We noticed that prolonged salt exposure did not alter flag leaf greenness even up to 6 weeks; however, it had a detrimental effect on panicle development especially in the salt-susceptible genotype Sabita. But more precise chlorophyll fluorescence imaging analysis revealed salinity-induced damages in Sabita. The salt-tolerant genotype Pokkali (AC41585), a potential Na+ excluder, managed to sequester higher Na+ load in the roots with little upward transport as evident from greater expression of HKT1 and HKT2 transporters. In contrast, the moderately salt-tolerant Lunidhan was less selective in Na+ transport, but possessed a higher capacity to Na+ sequestration in leaves. Higher K+ uptake and tissue-specific redistribution mediated by HAK and AKT transporters showed robust control in selective K+ movement from the root to flag leaf and developing panicles. On the contrary, expressions of Na+-specific transporters in developing panicles were either down-regulated or unaffected in tolerant and moderately tolerant genotypes. Yet, in the panicles of the susceptible genotype Sabita, some of the Na+-specific transporter genes (SOS1, HKT1;5, HKT2;4) were upregulated. Apart from the ionic regulation strategy, cellular energy balance mediated by different plasma-membrane and tonoplastic H+-pumps were also associated with the reproductive stage salt tolerance in rice.
KeywordsChlorophyll fluorescence imaging Flowering stage Ion channels Ion pumps Salinity Transporter
High-affinity potassium transporter
Salt overly sensitive
Stress stability index
Vacuolar type H+ ATPase
Yield stability index
We thank ICAR-National Rice Research Institute, Cuttack, Odisha, India, and National Innovations on Climate Resilient Agriculture (NICRA, EAP-245), Indian Council of Agricultural Research, New Delhi, for providing necessary facilities and funding to carry out the research.
Compliance with ethical standards
Conflict of interest
The authors declare no competing interests.
- Bonilla P, Dvorak J, Mackill D et al (2002) RLFP and SSLP mapping of salinity tolerance genes in chromosome 1 of rice (Oryza sativa L.) using recombinant inbred lines. Philipp Agric Sci 85:68–76Google Scholar
- Chakraborty K, Basak N, Bhaduri D et al (2018) Ionic basis of salt tolerance in plants: nutrient homeostasis and oxidative stress tolerance. In: Hasanuzzaman M, Fujita M, Oku H, Nahar K, Hawrylak-Nowak B (eds) Plant nutrients and abiotic stress tolerance. Springer, New York, pp 325–362CrossRefGoogle Scholar
- Gregorio GB, Senadhira D, Mendoza RD (1997) Screening rice for salinity tolerance. IRRI discussion paper series no. 22. Manila (Philippines), IRRI, pp 1–3Google Scholar
- Strasser RJ, Srivastava A, Tsimilli-Michael M (2000) The fluorescence transient as a tool to characterize and screen photosynthetic samples. In: Yunus M, Pathre U, Mohanty P (eds) Probing photosynthesis: mechanisms, regulation and adaptation. Taylor and Francis, London, pp 445–483Google Scholar
- Yamauchi S, Takemiya A, Sachenkamoto T et al (2016) The plasma membrane H+-ATPase AHA1 plays a major role in stomatal opening in response to blue light. Plant Physiol 171:2731–2743Google Scholar