Chemical activation of host defence mechanisms as a basis for crop protection

Comparative efficaciesin vitroof antibacterial, fungicidal, antioxidant, and herbicidal activities of momilatones A and B

“…A flavanone phytoalexin, sakuranetin that was isolated from ultraviolet irradiated rice leaves, showed great inhibition on spore germination of Pyricularia oryzae with the value of ED 50 (Effective Dose) of about 15 ppm (Kodama et al 1992). Previous research announced that M A and M B are triggered by pathogen infection, including fungi and virus (Cartwright et al 1977, Agrawal et al 2002, Jung et al 2005. M A which is induced in rice leaves as a phytoalexin occurs constitutively in rice seeds (Cartwright et al 1981).…”

“…M B differs from M A by a bridge in the ring A, attached with a hydroxyl group that may result in different strength of M A and M B in herbicidal, antibacterial, antifungal and antioxidant activities. All plant parts of rice such as leaves, hulls, straws, and rhizomes are known to possess M A and M B (Cartwright et al 1977, 1981, Kodama et al 1988, Lee et al 1999, Kato-Noguchi & Ino 2003a. Quantity of the M A and M B in rice increased to their maximal levels at the heading stage (120 days after seedling were about 4.6 and 3.1 mg/g dry weight, respectively), and then gradually decreased (180 days after seedling were 1.86 and 0.99 mg/g dry weight, respectively [Lee et al 1999]).…”

“…The diterpenoids (M A and M B ) were first isolated by Japanese scientists from rice husks (Kato et al 1973) and indicated by them as potential plant growth inhibitors. Since then, much work on momilactones conducted by many worldwide scientists has found that most parts of the rice plant contain M A and M B , including leaves, hulls, straws and root exudates (Cartwright et al 1977, 1981, Kodama et al 1988, Lee et al 1999, Kato-Noguchi & Ino 2003a. Both M A and M B are considered as phytoalexins of rice, and M A is regarded as a rice defense system against pathogens (Nojiri et al 1996, Tamogami & Kodama 2000, Agrawal et al 2002.…”

“…A large number of phytotoxic substances (allelochemicals) including diterpene and flavanone phytoalexins, which are involved in the defense mechanism of the rice plant have been isolated as phytoalexins such as M A and M B (Figure 1), oryzalexin A-F, phytocassanes A to D and the flavonoid phytoalexin sakuranetin (Cartwright et al 1977, Kodama et al 1992, Kato et al 1993, Tamogani et al 1993, Koga et al 1997, Chung et al 2005. The diterpenoids (M A and M B ) were first isolated by Japanese scientists from rice husks (Kato et al 1973) and indicated by them as potential plant growth inhibitors.…”

The application of synthetic biology to elucidation of plant mono-, sesqui- and diterpenoid metabolism

“…Arguably more importantly, this further enables investigation of the physiological function of the resulting natural products, which is particularly critical given the complex mixtures of compounds generally produced by plants that confound functions ascribed solely on the basis of in vitro analyses of natural product biological activity. For example, despite being the first rice diterpenoids suggested to act as phytoalexins against the devastating fungal blast pathogen Magneportha oryzae (Cartwright et al, 1977), the momilactones seem to be more important as allelochemicals that are constitutively secreted from the roots and suppress the growth of other plant species . This is consistent with the original isolation of the momilactones as plant growth inhibitors (Kato et al, 1973), and more recent work on rice allelopathy (Kato-Noguchi and Peters, 2013), although it should be noted that some evidence has been presented indicating a role for the momilactones (or related OsCPS4-dependent diterpenoids) as phytoalexins (Toyomasu et al, 2013).…”