## 2 Diversity and Distribution of Rice Phytoalexins
### Phenolic Phytoalexins in Rice
Interestingly, sakuranetin can be detoxified into naringenin and sternbin (another flavanon compound) by _M. grisea_[92] and into naringenin, sakuranetin-4\({}^{\prime}\)-O-\(\beta\)-d-xylopyranoside, and naringenin-7-O-\(\beta\)-d-xylopyranoside by the rice sheath blight fungus _R. solani_[93]. Until recently, sakuranetin was considered the only phenol phytoalexin in rice. However, recent studies have shown that several phenylamides (e.g., _N_-cinnamoyltyramine, _N_-benzoylryptamine, _N_-feruolylryptamine, _N_-cinnamoylryptamine, _N_-feruolylytramine, _N_-_p_-coumaroylserotonin, and _N_-feruolyserotonin) (Figure 4) are produced by rice in response to biotic or abiotic stress. Phenylamides are secondary metabolites widely distributed in plants resulting from the conjugation of mono- or polyamines with aromatic acids, like caffeic, ferulic, and _p_-coumaric acids [94]. Amine moieties found in rice phenylamides include the arylmonoamines tyramine,ryptamine, and serotonin [21]. Some of the phenylamides found in rice have shown significant antimicrobial activity against several bacterial and fungal pathogens such as _Burkholderia glumae_, _Xanthomonas oryzae_, _Magnuporthe grisea_, and _Cochliobolus miyabeanus_[74; 95; 96]. This observation strongly suggests that, together with sakuranetin, phenylamides are members of phenolic phytoaleoxins in rice [21; 96]. [PERSON] and co-workers [97; 98] identified several phenylamides, including _N_-_p_-coumaryiscentonin (CouSer), _N_-feruolylryptamine (FerTry), and _N_-feruolyserotonin (FerSer), in rice leaves infected with the blast fungus _M. oryzae_ and the rice brown spot fungus _B. oryzae_. [PERSON] and colleagues [99] observed that salt stress in leaves of the salt-resistant rice cultivar Pokkali led to an increase in putrescine amides, which are presumably conjugated with phenolic acids or other low molecular weight compounds. UV-induced accumulation of _N_-benzoylryptamine (BenTry) and _N_-_trans_-cinnamoyltyramine (CinTyr) in rice was also observed by [PERSON] and colleagues [100]. _N_-Benzoyltyramine (BenTyr) was isolated from rice leaves exposed to UV radiation by [PERSON] et al. [95]. The production of this compound was also induced by inoculation with _M. oryzae_. However, unlike CinTyr and BenTry, BenTyr has shown negligible antifungal activity against this pathogen, and further antimicrobial testing is needed to investigate its possible role in plant defense against pathogen attack. To provide a full picture of inducible phenylamides in rice, [PERSON] and co-workers [96] monitored the accumulation of 25 phenylamides in rice leaves after infection with _C. miyabeanus_ and _X. oryzae_. Both pathogens caused significant increases in phenylamide accumulation, although the greatest effects were recorded after _C. miyabeanus_ infection, which mainly induced the accumulation _N_-feruolylputrescine (FerPut), BenTry, and _N_-benzoylserotonin (BenSer), followed by BenTry, _N_-_trans_-cinnamoylserotonin (CinSer), CouSer, FerSer, CinTyr, _N_-feruolylagmatine (FerAgm), and _N_-_trans_-cinnamoylryptamine (CinTyr). Phenylamide accumulation has also been induced by treatment with different hormones, including jasmonic acid, salicylic acid, and 6-benzylaminopurine.