are capable of detoxifying HCN  while others are capable of cyanide-resistant respiration . While there is indisputable evidence for a role of cyanogenic glycosides as herbivore deterrents [72,82], there is little reliable evidence for direct roles against pathogens [17,83]. Very early studies have related the Fusarium wilt resistance of flax to HCN release in roots . HCN release occurs in leaves of Lotus corniculatus upon pathogen invasion arresting the development of most fungal species . A recent study in barley investigated five leucine-derived cyano glycosides however discovered Inhibitors,research,lifescience,medical that the β-glucosidase that hydrolyses them is only present in the endosperm of germinating barley therefore concluding that the cyanide potential of barley cannot be harnessed in a fungal attack . High performance liquid chromatography (HPLC) and LC-MS/MS for the analysis and identification of cyanogenic glycosides has recently been exploited for the sensitive detection of these compounds Inhibitors,research,lifescience,medical and their derivatives [85-87]. The potential of these techniques should be utilised to confirm the role of these compounds in plant defence. 6. Saponins Saponins are a class of Inhibitors,research,lifescience,medical glycosylated triterpenes; steroids and steroidal alkaloids synthesised
from the Necrostatin-1 in vivo mevalonate or non-mevalonate pathway in plants (Figure 1) and are absent in the majority of monocotyledon plants and all cereals with the exception of oat (Avena). These phytoanticipans possess a broad range of biological activities including antimicrobial, insecticidal, allelopathic action and molluscidal acitivity [17,88]. Oat contains two types of Saponins—Four triterpenoid avenacins and two steroidal Inhibitors,research,lifescience,medical avenacosides (Figure 1) present in roots and leaves respectively [89,90]. Avenacins are active in their natural glycoslyated
form in the plant in contrast to avenacosides, benzoxazanoids and many other antifungal compounds which are active only in their aglycone forms [91,92]. The inactive avenacosides Inhibitors,research,lifescience,medical are stored in the vacuole of the plant and activated when tissue damage caused by pathogenic fungi disrupts membranes allowing the plant enzyme β-glucosidase to hydrolyse the D-glucose unit forming the biologically active aglycone . The active form of the avenacosides then forms complexes with membrane sterols disrupting Astemizole the fungi’s plasma membrane by pore formation resulting in fungal cell death. Avenacins, which are active in their native form, are also stored in the vacuole of plants, which are protected from their toxic effects by a different membrane sterol composition [17,89,94]. In line with this, several fungi are resistant to saponin-producing plants due to their natural membrane composition. The biological activity and biosynthesis of saponins has been recently reviewed .