The Influence of Mycorrhizal Fungi on the Accumulation of Sennosides A and B in Senna alexandrina and Senna italica

Symbiotic arbuscular mycorrhizal fungi (AMF) play a major role in plant development, growth, and relationships with the environment through a change in the accumulation of secondary metabolites; hence, we planned to investigate AMF’s influence on sennoside A and B accumulation in Senna alexandrina (SA) and Senna italica (SI). Seeds of SA (S. alexandrina free of mycorrhizae) and SI (S. italica free of mycorrhizae) were planted in two types of soils: +mycorrhiza and—mycorrhiza. The plant leaves of SA, SI, S. alexandrina with mycorrhizae (SAM) and S. italica with mycorrhizae (SIM) were collected and extracted (with 85% methanol), and sennoside A and B content was evaluated by the HPLC–UV method. The antioxidant activity of SA, SI, SAM and SIM was evaluated by using 2, 2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) methods, while antimicrobial properties were evaluated by the minimum inhibitory concentration method (MIC). The AMF colonization was 85.66% and 85%, respectively, in the roots of SA and SI. The HPLC analysis showed a significant increase in (%) the content of sennoside A/sennoside B by 71.11/88.21, respectively, in SAM and 6.76/36.37 in SIM, which clearly indicated positive AMF effects. The DPPH/ABTS [The half maximal inhibitory concentration (IC50): 235.9/321.5 µg/mL] scavenging activity of SAM was comparatively higher and it also exhibited strong antibacterial action (MIC: 156.25 µg/mL), which supported the increase in sennoside content. This finding may be useful for further investigations of the symbiotic relation of mycorrhizal fungi with other plant species.