Role of proline accumulation in salinity tolerance of rice seedlings under NaCl stress

Abstract:

The trend toward expanding rice cultivation into salt-affected lowlands of East Africa has made salinity tolerance a priority breeding target. This research compared proline accumulation, growth responses, and ion homeostasis in a salt-tolerant rice genotype (Pokkali) and a salt-sensitive genotype (IR29) under seven NaCl concentrations (0, 25, 50, 75, 100, 125, 150 mM) in a hydroponic system at the Oromia Institute of Agricultural Sciences, Jimma, Ethiopia, during 2023. A completely randomised design with factorial arrangement and three replications was used. Proline content in Pokkali rose from 1.2 to 12.8 micromol/g FW across the salinity gradient, roughly double the accumulation in IR29 (1.1 to 6.4 micromol/g FW). Shoot length declined by 62% in IR29 at 150 mM but only by 38% in Pokkali. The tolerant genotype maintained a lower Na⁺/K⁺ ratio (1.8 vs 4.7 in IR29 at 150 mM). A strong negative correlation (r = -0.91) between proline content and Na⁺/K⁺ ratio in Pokkali supports the hypothesis that proline contributes to osmotic adjustment and ion exclusion. These results confirm proline accumulation as a reliable biochemical marker for screening salt tolerance in rice.