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

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 nonsalinised 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 (AFLPbands) 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.

A new screening technique for salinity resistance in rice (Oryza sativa L.) seedlings using bypass flow

“…Of the cereals, rice is the most salt‐sensitive crop as it is ineffective in controlling the influx of Na + across the roots, leading to the rapid accumulation of toxic concentrations in the shoots (Yeo et al . 1990; Roshandel & Flowers 2009; Singh & Flowers 2011). The effects of salinity on rice have been reported to reduce seed germination (Lutts, Kinet & Bouharmont 1995; Hakim et al .…”

Effect of salinity and radiation on proline accumulation in seeds of canola (Brassica napus L.)

“…This reason for such stress may be soil salinity. For some stress proteins rich proline content is typical (Jofre andBecker 2009, Roshandel andFlowers 2009). These compounds are known as proline-rich glycoproEffect of salinity and radiation on proline accumulation in seeds of canola (Brassica napus L.)…”

Screening for salinity tolerance of Oryza glaberrima Steud. seedlings

“…Beside restriction of Na + absorption and translocation, tolerance of photosynthetic tissues to the accumulated toxic ions is an important component of salinity resistance in plants (Roshandel and Flowers, 2009). It implies that biochemical protecting compounds have to be synthesized and/or that compartmentation processes leading to Na + accumulation in apoplasm or vacuoles must be operating to limit the deleterious impact of toxic ion on cytoplasm where the major steps of cell metabolism occur.…”