Effect of vitamin C and folic acid on seed vigour response and phenolic-linked antioxidant activity

Folic acid and vitamin C were used in the concentration range of 0–500 μM as exogenous growth enhancers to stimulate pea (Pisum sativum) seedling vigour. The results suggest that a concentration of 50 μM folic acid and 500 μM vitamin C were optimum in maximally enhancing seed vigour and potentially seedling performance according to both agronomic and biochemical seed vigour parameters. Results indicated that germination percentage, shoot weight, shoot height, and root length were enhanced in folic acid and vitamin C treated plants compared to control plants. The levels of enhanced phenolic content in response to folic acid and vitamin C treatments were highest on days 8 and 10. Evaluation of critical biochemical parameters indicated that the average glucose-6-phosphate dehydrogenase (G6PDH) activity and proline content in response to treatments were higher than control and correlated to enhanced phenolic content and DPPH-based antioxidant activity. Key enzymes, guaiacol peroxidase (GPX), superoxide dismutase (SOD), and catalase (CAT) were also higher in response to treatments and correlated to enhanced phenolic content and DPPH-based antioxidant activity. Taken together, these studies support the hypothesis that the proline-linked pentose phosphate pathway stimulates phenolic synthesis and related free-radical scavenging antioxidant activity. Further, this proline-linked pentose phosphate pathway stimulation in response to folic acid and vitamin C was also correlated to antioxidant enzyme response indicated by the stimulation of GPX, SOD, and CAT activities. Therefore, this study indicates the enhancement of seed vigour response by folic acid and vitamin C as reflected in both agronomic and biochemical responses, and this occurred through the stimulation of phenolic-linked antioxidant response that is likely positively modulated through the proline-linked pentose phosphate pathway.