Potential of ultrasound and nicotinic acid to improve physiological responses and trigonelline biosynthesis in fenugreek (Trigonella foenum-graecum L.)

Fenugreek (Trigonella foenum-graecum L.) is an important source of trigonelline, a valuable anti-diabetic metabolite. The main objective of this study was to investigate the possibility of ultrasonication and nicotinic acid feeding in stimulating trigonelline biosynthesis and antioxidant system. For this purpose, the seeds were ultrasonicated in three groups for 0, 5, and 10 min at 40 kHz at 25 ?C. Seedlings were treated after the emergence of the first true leaves (10 days) with Hoagland's solution complemented with 0, 2, 4 mg L-1 nicotinic acid. The results showed that the 5 min ultrasound priming of fenugreek seeds improved germination-related traits compared with the control culture. However, the 10 min ultrasound priming negatively affected and reduced the germination traits. The highest values of growth indices of seedlings were recorded under effect of 5 min ultrasound and 4 mg L-1 nicotinic acid. Ultrasound and nicotinic acid individually and as combined decreased photosynthetic pigments (chlorophylls and carotenoids). The interaction between the two factors increased the antioxidant compounds and biochemical levels of seedlings compared with the control treatment. The highest increase in trigonelline content (170.9 mg/100 g FW) was observed under 5 min ultrasound and 2 mg L-1 nicotinic acid feeding. Generally, it appears that ultrasound potentiated the effect of nicotinic acid feeding on defense responses and the production of secondary metabolites, including trigonelline biosynthesis. Overall, it can be concluded that 5 min ultrasound seed priming and 2 mg L-1 nicotinic acid can improve growth indices, and therefore to achieve optimal biomass yield and trigonelline production is recommended in fenugreek cultivation.