Seed Halopriming Improves Salinity Tolerance of Some Rice Cultivars During Seedling Stage

Abstract

Background: Saline land in coastal areas has great potential for crop cultivation. Improving salt tolerance in rice is a key to expanding the available area for its growth and thus improving global food security. Seed priming with salt (halopriming) can enhance plant growth and decrease saline intolerance under salt stress conditions during the subsequent seedling stage. However, there is little known about rice defense mechanisms against salinity at seedling stages after seed halopriming treatment. This study focused on the effect of seed halopriming treatment on salinity tolerance in a susceptible cultivar, IR 64, a resistant cultivar, Pokkali, and two pigmented rice cultivars, Merah Kalimantan Selatan (Merah Kalsel) and Cempo Ireng Pendek (CI Pendek). We grew these cultivars in hydroponic culture, with and without halopriming at the seed stage, under either non-salt or salt stress conditions during the seedling stage.

Results: The SES scoring assessment showed that the level of salinity tolerance in susceptible cultivar, IR 64, and moderate cultivar, Merah Kalsel, improved after seed halopriming treatment. Furthermore, seed halopriming improved the growth performance of IR 64 and Merah Kalsel rice seedlings. Quantitative PCR revealed that seed halopriming induced expression of the OsNHX1 and OsHKT1 genes in susceptible rice cultivar, IR 64 and Merah Kalsel thereby increasing the level of resistance to salinity. The expression levels of OsSOS1 and OsHKT1 genes in resistant cultivar, Pokkali, also increased but there was no affect on the level of salinity tolerance. On the contrary, seed halopriming decreased the expression level of OsSOS1 genes in pigmented rice cultivar, CI Pendek, but did not affect the level of salinity tolerance. The transporter gene expression induction significantly improved salinity tolerance in salinity-susceptible rice, IR 64, and moderately tolerant rice cultivar, Merah Kalsel. Induction of expression of the OsNHX1 and OsHKT1 genes in susceptible rice, IR 64, after halopriming seed treatment balances the osmotic pressure and prevents the accumulation of toxic concentrations of Na⁺, resulting in tolerance to salinity stress.

Conclusion: These results suggest that seed halopriming can improve salinity tolerance of salinity-susceptible and moderately tolerant rice cultivars.

Keywords: Salinity tolerance; Seed halopriming; Seedling stage; Standard Evaluation System for Rice (SES); Transporter genes.

Fig. 1

Most of the tested cultivars were less affected by salinity stress after priming. For each cultivar, an example of the following treatment groups is shown: (from left to right) a unprimed and non-stressed, b unprimed and stressed with 200 mM NaCl solution, c primed and non-stressed, and d primed and stressed with 200 mM NaCl solution

Fig. 2

Effect of salinity stress on agronomic parameters of rice plants. a Chlorophyll content, b relative water content (RWC). Chlorophyll contents were measured for 7 days after salinity treatment; relative water content in the whole plant with and without priming was measured 7 days after salinity stress. Values are means of three replicates ± SE. *p < 0.05, **p < 0.01, LSD test

Fig. 3

Effect of salinity stress on agronomic parameters of rice plants. a Plant height and root length and b dry weight of whole plant with and without priming were measured 7 days after salinity stress. Values are means of three replicates ± SE

Fig. 4

Concentration of Na⁺ and K⁺ ions of rice plants after 7 days exposed to salinity stress. a, c Na⁺ and K⁺ ion concentration in roots. b, d Na⁺ and K⁺ ion concentration in leaves were measured at 0, 4, and 7 days of salinity treatment (200 mM NaCl). Values are means of three replicates ± SE. *p < 0.05, **p < 0.01, LSD test. DW: dry weight

Fig. 5

Relative expression of transporter genes in roots and leaves as compared with UBIQUITIN. Expression was measured at 0, 6, and 24 h after salinity treatment (200 mM NaCl). Values are means of three replicates ± SE