Abstract
The study was couducted to investigate the effects of gamma irradiation and CO2 on flavonoid content and leaf gas exchange in C.asiatica. For flavonoid determination, the design was a split split plot based on Randomized Complete Block Design (RCBD). For other parameters, the designs were split plots. Statistical tests revealed significant differences in flavonoid contents of Centella asiatica leaves between different growth stages and various CO2 treatments. CO2 400, G20 (400 = ambient CO2; G20 = Plants exposed to 20 Gy) showed 82.90% higher total flavonoid content (TFC) in the 5th week than CO2 400 as control at its best harvest time (4th week). Increasing the concentration of CO2 from 400 to 800 μmol/mol had significant effects on TFC and harvesting time. In fact, 800 μmol/mol resulted in 171.1% and 66.62% increases in TFC for control and irradiated plants, respectively. Moreover, increasing CO2 concentration reduced the harvesting time to three and four weeks for control and irradiated plants, respectively. Enhancing CO2 to 800 µmol/mol resulted in a 193.30% (CO2 800) increase in leaf biomass compared to 400 µmol/mol and 226.34% enhancement in irradiated plants (CO2 800, G20) [800 = Ambient CO2; G20 = Plants exposed to 20 Gy] than CO2 400, G20. In addition, the CO2 800, G20 had the highest amount of flavonoid*biomass in the 4th week. The results of this study indicated that all elevated CO2 treatments had higher PN than the ambient ones. The findings showed that when CO2 level increased from 400 to 800 µmol/mol, stomatal conductance, leaf intercellular CO2 and transpiration rate had the tendency to decrease. However, water use efficiency increased in response to elevated CO2 concentration. Returning to the findings of this study, it is now possible to state that the proposed method (combined CO2 and gamma irradiation) has the potential to increase the product value by reducing the time to harvest, increasing the yield per unit area via boosting photosynthesis capacity, as well as increasing biochemicals (flavonoids) per gram DM.
Highlights
The daily intake of flavonoids in normal food, fruits and vegetables, is 1–2 g
Statistical tests revealed significant differences in flavonoid contents of Centella asiatica leaves between different growth stages and various CO2 treatments
compared to μmol/mol (CO2 400), G20 (400 = Ambient CO2; G20 = Plants exposed to 20 Gy) showed 82.90% higher total flavonoid content (TFC) than CO2 400 as control
Summary
The daily intake of flavonoids in normal food, fruits and vegetables, is 1–2 g. It is important to highlight that limited information exists on the potential and extent of enhanced production of secondary metabolites using physical elicitors, such as gamma radiation [2]. Gamma radiation can interact with atoms and molecules to build up free radical levels in cells that cause modifications in important components of plant cells. It may induce remarkable morphological changes in plant tissues, as well as various biochemical responses at the cellular level. Papers by Kim and colleagues [11] have supported the hypothesis that gamma irradiation will induce growth stimulation by altering the hormonal signaling system in plant cells or increasing cells antioxidant activity to overcome daily environmental stress. It is expected that CO2 and gamma irradiation would have synergistic effects to boost flavonoids in the leaves of C.asiatica
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