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The ionic effects of NaCl on physiology and gene expression in rice genotypes differing in salt tolerance

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Abstract

The effects of ionic stress on the physiology and gene expression of two rice genotypes (IR4630 and IR15324) that differ in salt tolerance, were investigated by evaluating changes in the biomass, Na+ and K+ concentrations and applying the cDNA-AFLP technique to highlight changes in gene expression. Over 8 days of salinisation, the effect of NaCl on the reduction of biomass (dry weight) was apparent from 24 h after salinisation (the first time point), indicating that the consequences of the build up of Na+ (and Cl-) in the leaves of both lines was rapid. Furthermore, root growth of IR15324 was much more sensitive to salt than that of IR4630 (the reduction in root dry weight compared to non-salinised plants was three times greater in IR15324 than IR4630). The two rice lines also differed in their Na+ accumulation in saline conditions, a difference that was more marked in the shoots, particularly at the final harvest, than in the roots. Under salt stress, the K+ content (µmol/shoot) increased over four successive harvests (24, 48, 96, 192 h) in both lines, but was always greater in IR4630 than in IR15324: differences in Na+/K+ ratio appear to be an important determinant of salt tolerance in rice. To separate osmotic from ionic effects of salt, mannitol was applied as a non-ionic osmoticum at an osmotic potential estimated to be equivalent to 50 mM NaCl. Messenger RNA was sampled at 0.5, 6, 24, 48 and 192 hours after salinisation. Several products (AFLP-bands) were detected, which were upregulated in the response to ionic effects of salt in the tolerant line (IR4630) and not expressed in the sensitive line (IR15324). Bioinformatic analysis indicated three of these AFLP-bands have a high-degree of sequence similarity with the genes encoding a proline rich protein, senescence associated protein and heat-shock protein. The data are novel in that they differentially highlight changes induced by the ionic rather than osmotic effects of salt and in a tolerant rather than a sensitive genotype. The possible roles of the products of these genes are discussed.

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Abbreviations

AFLP:

Amplified fragment length polymorphism

ATP:

adenosine tri-phosphate

cDNA:

complementary DNA

dNTP:

deoxynucleotide tri-phosphate

ds-cDNA:

double stranded cDNA

HSP:

heat shock protein

PAR:

photosynthetically active radiation

PEG:

polyethylene glycol

PRP:

proline-rich protein

RT-PCR:

reverse-transcription polymerase chain reaction

SAG:

senescence associated gene

X-GAL:

5-bromo-4-chloro-3-indolyl-B-d-galactoside

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Acknowledgment

The authors wish to thank Dr. Mike Malone for his help and encouragement. These experiments were conducted at the School of Life Science of the University of Sussex, Brighton, UK and supported by a scholarship from the Ministry of Sciences, Research and Biotechnology, Iran.

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Correspondence to Parto Roshandel.

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Responsible Editor: John McPherson Cheeseman.

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Roshandel, P., Flowers, T. The ionic effects of NaCl on physiology and gene expression in rice genotypes differing in salt tolerance. Plant Soil 315, 135–147 (2009). https://doi.org/10.1007/s11104-008-9738-6

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  • DOI: https://doi.org/10.1007/s11104-008-9738-6

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