Alfalfa (Medicago sativaL.) shoot saponins: identification and bio-activity by the assessment of aphid feeding

Abstract

Biochemical components in alfalfa (Medicago sativa L.), such as saponins, can act as protecting factors against bio-stresses. Saponins are also antifeedants and show oral toxicity towards higher and lower animals. Changes in saponins, such as variation in the carbon skeleton, or hydrolysis of saponin glycosides and other conjugates, may change their biological effects. The aims of this research were to study saponin variation in different growth stages of alfalfa and to investigate the biological role of saponins in the spotted alfalfa aphid, Therioaphis maculata. Saponins from alfalfa shoots in different growth stages were extracted, chemically purified and analysed by TLC. Specific saponins such as soyasaponin1 from root and shoot and two bisdesmosides of medicagenic acid, one from shoot and another from root tissues, were identified using reference compounds allowing changes in saponin composition during plant development in different shoot tissues of alfalfa to be assessed. The response of the alfalfa aphid to feeding on alfalfa in different growth stages was studied. No significant difference in the survival of aphids, from neonate to adult, was observed, but due to the antibiotic effects of saponins, two differences were found in the onset of nymph production and cumulative nymph production. The results show that the saponin composition in alfalfa changes with plant development and this, in turn, can often negatively affect the development of specific insect pests such as the spotted alfalfa aphid, suggesting a possible biological role of alfalfa saponins.

Nutritional Aspects of Ecologically Relevant Phytochemicals in Ruminant Production

“…In angiosperm monocotyledons and angiosperm dicotyledons plants, the variation, composition, concentration, distribution, and differential bio-activity of TPS are influenced by plant growth, agronomic and genotype-environmental interactions (132)(133)(134). Moreover, TPS-plant storage, physical milling, TPS separation, and the bio-accessibility of metabolites in the form of concentrated extracts, derivatives, or food additives to facilitate human-animal utilization may modify aglycones' structure and their bio-physiological, nutraceutical, and pharmaceutical activities (121,124,135).…”

Molecular Cloning and Functional Identification of a Squalene Synthase Encoding Gene from Alfalfa (Medicago sativa L.)

“…These unfavorable effects have restricted the optimum use of alfalfa in animal feed. On the other hand, ASs were found to negatively affect the development of spotted alfalfa aphid and were effective to control rice blast by preventing the fungal attack of several rice cultivars [30,31]. Hence, investigation of the biosynthesis pathway of saponins may facilitate the regulation of saponin production at appropriate levels in alfalfa, which would benefit the health of both animal and plant.…”

Salinity Stress Alters the Secondary Metabolic Profile of M. sativa, M. arborea and Their Hybrid (Alborea)

“…Accumulation of such compounds has been associated with a plethora of biological activities, including seed germination, allelopathy, poor digestibility and beneficial anti-pathogen (including fungi and insects) properties [ 43 ]. Moreover, M. arborea has high allelopathic potential that affects the growth and germination of other species [ 44 ].…”

“…Special attention should be given to triterpenoid compounds and their accumulation upon abiotic stresses, as they may contribute to fortification of plant membranes. Moses et al, 2014 and Pulvento et al, 2012 [ 43 , 47 ] studied the response of quinoa plants (a salt-tolerant species) under conditions of increased salinity and found that the plants had accumulated high levels of saponins compared to control plants. Another study that correlated saponins with plant salinity tolerance was conducted by Oku et al, 2003 [ 48 ] in which the concentration of triterpenoids increased significantly under high salinity in both shoots and roots of Kandeliacandel and Bruguieragymnorrhiza.…”

“…In several studies, salt tolerance was tightly linked to higher accumulation of phenolic compounds [ 60 , 61 , 62 ]. A very popular strategy to induce the production of several polyphenols is by application of stress hormones [ 39 , 43 ]. Given that M. arborea’s seedling growth was superior compared to the other two entries under acute stress it seems that its production of secondary metabolites, and in particular the production of saponins and polyphenols, had a positive effect under salt stress conditions without metabolic costs.…”