Relationship between morphological traits and expression of HKT1;5 gene in genetically modified rice genotypes under salinity stress

Salinity is one of the most important post-drought abiotic stresses that limits rice cultivation and productivity in all regions of the world. The level of salinity tolerance depends largely on the genetic makeup of the cultivars. This study aimed to evaluate the response of four genetically modified rice genotypes to different salinity levels by examining some morphological traits and analyzing the gene expression of the HKT1;5 gene, which is associated with salt tolerance mechanisms. The results indicated a clear variability among genotypes in their responses to salt stress. Plant height and leaf area decreased significantly at high stress (S2), with genotype V2 recording the highest plant height (97.95 cm), while cultivar V1 achieved the largest leaf area (74.84 cm²). Different plant varieties reacted differently to salt. When salt was high, plants became shorter and had smaller leaves. Genotype V2 was the tallest (97.95 cm), and cultivar V1 had the largest leaves (74.84 cm²). V3 recorded the highest dry weight (115.23 g). Its weight increased slightly with the addition of a small amount of salt, then decreased with increasing salt. The 1000-grain weight remained roughly constant, but the total grain and plant yield decreased with increasing salt. The genotype V1 recorded the highest values (43.71 g/plant for grain and 136.92 g for biological yield in S1). In contrast, V4 performed poorly in all traits. Gene expression analysis revealed clear genetic variation in the induction of the HKT1;5 gene under salt stress. The expression level remained close to the control level (≈1) in S0, while it increased significantly in V1, V2, and V3, reaching (3.25-, 6.75-, and 8.16-fold, respectively) in S2. Genotype V4 also showed a limited response (1.73-fold), reflecting its poor adaptive capacity. Therefore, genotypes V3 and V1 appear to handle salt very efficiently by controlling sodium uptake. On the other hand, the genotype V4 seems to have the most sensitive to salt. Because V3 is the strongest, it could really help with breeding rice that can stand up to salty conditions.