Cajanus cajan (L.) Huth (Fabaceae) is a food legume of considerable nutritional and functional significance. This study examined the comparative effects of salt stress on seed germination, hydroponic growth, and phytochemical accumulation across two developmental stages: 10-day-old germinated seeds and 45-day-old hydroponically grown plants, using NaCl solutions at concentrations of 0, 25, 50, 75, 100, and 150 mM. Both germination rate and growth were greatest at 0–25 mM NaCl, with performance declining at higher concentrations. LC–MS/MS analysis of free amino acids in 10-day-germinated seeds revealed a salt-induced metabolic shift. Proline, leucine, and phenylalanine were the dominant free amino acids and increased progressively with rising NaCl concentrations. Phytochemical profiling by HPLC identified gallic acid, catechin, and genistin as the major compounds, with increased levels under salinity stress. Germinated seeds at 150 mM NaCl, germinated seeds exhibited the highest phytochemical accumulation, with total phenolic content (TPC), total flavonoid content (TFC), and DPPH activity reaching 18.192 ± 0.020 mg GAE/g extract, 8.519 ± 0.026 mg QE/g extract, and 11.623 ± 0.284 mg AAE/g extract, respectively. Phytochemical responses in 45-day hydroponic plants varied by tissue type. Leaves exhibited declining TPC and TFC with increasing NaCl (from 29 to 16 mg GAE/g and 41 mg QE/g extract), while stems showed the opposite trend, reaching 18 mg GAE/g and 21 mg QE/g extract at 50 mM. Root tissues maintained comparatively low phytochemical levels throughout. Notably, DPPH scavenging capacity increased across all tissues under salt stress, with peak values of 12–13 µg AAE/g extract recorded at 50 mM NaCl. These results indicate that salt stress exerts stage- and organ-dependent effects on phytochemical accumulation in C. cajan. High salinity during germination stimulates bioactive compound production, whereas moderate salinity appears to be the threshold at which antioxidant capacity is maximized in hydroponic systems. These observations point to the practical utility of controlled salt elicitation as a strategy for enriching pigeon pea with health-promoting phytochemicals, reinforcing its potential as a functional food crop.
Chookhampaeng et al. (Sun,) studied this question.
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