Detoxification of Saponins

Many plants constitutively produce triterpenoid, steroid or steroidal glycosylated compounds that are generally inhibitory to fungi (Figure 4.9). These are known by the general term saponin because of their soap-like properties, derived from the plant Saponaria officinalis, the extracts of which were once used to make soap (Osbourn, 1996). Saponins make complexes with membrane sterols, resulting in pore formation and leakage of cell constituents. The leaves and green fruits of the tomato plant contain high levels a steroidal glycoalkaloid, called tomatine (Figure 4.10). The pathogenecity of Septoria lycopersici (Anamorphici) on tomato plants was attributed to the production of a glycosyl hydrolase, tomatinase (Arneson and Durbin, 1967), which detoxifies tomatine by removing a single terminal glucose molecule by hydrolysis of a (3,1-2 linkage. The targeted gene-disruption technique was used to test the role of saponins in pathogenecity. The root-infecting fungus Gaeumannomyces graminis var. tritici (Ascomycotina) causes the "take-all" disease of wheat and barley but is unable to infect oat because of its inability to detoxify the saponin avenacin A-1 that is present in oats. G. graminis var. tritici can, however, infect a wild oat species that did not produce avenacin A-1. The gene encoding avenacinase was cloned and used to disrupt avenacinase by site-directed mutagenesis of the genomic copy in var.

Figure 4.9 Chemical structures of saponins. Avenacin A-1 is a triterpenoid saponin in oat root. a-Tomatine is tomato steroidal glycoalkaloid. Avenaconaside B is an oat leaf saponin. These three saponins have a sugar chain attached to carbon-3 via oxygen. Avenaconaside B has an additional sugar moiety (P-D-glucose) attached via oxygen to c-26. Avenaconaside A differs from avenaconaside B in that it lacks the terminal P(1-3)-linked D-glucose molecule. The removal of C-26 glucose by the pathogen is indicated by an asterisk. (From Osbourn (1996).)

Figure 4.9 Chemical structures of saponins. Avenacin A-1 is a triterpenoid saponin in oat root. a-Tomatine is tomato steroidal glycoalkaloid. Avenaconaside B is an oat leaf saponin. These three saponins have a sugar chain attached to carbon-3 via oxygen. Avenaconaside B has an additional sugar moiety (P-D-glucose) attached via oxygen to c-26. Avenaconaside A differs from avenaconaside B in that it lacks the terminal P(1-3)-linked D-glucose molecule. The removal of C-26 glucose by the pathogen is indicated by an asterisk. (From Osbourn (1996).)

Septoria lycopersici Verticillium albo-atrum

Septoria lycopersici Verticillium albo-atrum

Lycopersici
f.sp. lycopersici Botrytis cinerea

Figure 4.10 Detoxification of saponins by tomato pathogens. (From Osbourn (1996).)

avenae. The var. avenae transformants lost pathogenecity to oats but not to wheat. These examples suggest the role of saponin detoxifying enzymes in pathogenesis.

Detoxification and Weight Loss

Detoxification and Weight Loss

Detoxification is something that is very important to the body, but it is something that isn't understood well. Centuries ago, health masters in the East understood the importance of balancing and detoxifying the body. It's something that Western medicine is only beginning to understand.

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