# Rice Secondary Metabolites: Structures, Roles, Biosynthesis, and Metabolic Regulation
## 2 Structural Diversity and Roles of Rice Secondary Metabolites
### Alkaloids and Their Biological Functions  
2-Acetyl-1-pyrroline (2 AP, **248**) is an important nitrogen-containing aroma compound that gives aromatic rice its characteristic flavor [113]. The concentration of 2 AP (**248**) in uncooked Khao Dawk Mali 105 brown rice was quantitatively analyzed by capillary GC and found to be 0.34 \(\mu\)g/g [114]. This compound also occurs naturally in some other plants such as _Pandanus anaryllifolius_ leaves and _Vallaris glabra_ flowers [14]. Proline was proved to be the precursor for the biosynthesis of 2 AP (**248**) in aromatic rice [115].  
The main alkaloids in rice are phenylamides containing an indole ring. Rice plants accumulate phenylamides in response to a pathogen attack. If rice leaves are infected with the pathogens _Cochliobolus miyabeanus_ and _Xanthomonas oryzae_, phenylamides are induced. They include \(N\)-feruloylagmatine (FerAgm, **244**), \(N\)-feruloylputrescine (FerPut, **245**), \(N\)-benzoylserotonin (BenSer, **249**), \(N\)-benzoytryptamine (BenTry, **250**), \(N\)-benzoylytramine (BenTyr, **251**), \(N\)-_trans-cinnamoylserotonin (CinSer, **252**), \(N\)-_trans-cinnamoyltryptamine (**253**), \(N\)-_trans-cinnamoyltyramine (CinTyr, **254**), \(N\)-_p-coumaroylserotonin (CouSer, **255**), and \(N\)-feruloylserotonin (FerSer, **256**). Some of these phenylamides displayed antimicrobial activity against _C. miyabeaunus_ and _X. oryzae_, indicating that they are phytoalexins [116]. Rice alkaloids and their biological activities are listed in Table 8. Their structures are shown in Figure 8.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Name** & \begin{tabular}{c} **Rice Part Used for** \\ **Isolation** \\ \end{tabular} & \
\begin{tabular}{c} **Biological Activity and** \\ **function** \\ \end{tabular} & **Ref.** \\ \hline \(N\)-Feruloylagmatine (**244**) & Leaves & Antimicrobial activity & [116] \\ \(N\)-Feruloylputrescine (**245**) & Leaves & Antimicrobial activity & [116] \\ \(N\)-Kynurenic acid (**246**) & Leaves & - & [34] \\ \(N\)-Lycoperodine-1 (**247**) & Leaves & - & [34] \\ \(2\)-Acetyl-1-pyrroline (**248**) & Grains & - & [113] \\ \(N\)-Benzoylserotonin (**249**) & Leaves & Antimicrobial activity & [116] \\ \(N\)-Benzoyltryptamine (**250**) & Leaves & Antimicrobial activity & [116] \\ \(N\)-Benzoyltryptamine (**251**) & Leaves & Antimicrobial activity & [58] \\ \(N\)-_trans-Cinnamoylserotonin (**252**) & Leaves & Antimicrobial activity & [116] \\ \(N\)-_trans-Cinnamoyltryptamine (**253**) & Leaves & Antimicrobial activity & [116] \\ \(N\)-_trans-Cinnamoyltryptamine (**254**) & Whole rice plant & Allelopathic activity & [117] \\ \(N\)-_trans-Cinnamoyltyramine (**255**) & Leaves & Antimicrobial activity & [58] \\ \(N\)-_p-Coumaroylserotonin (**255**) & Leaves & Antimicrobial activity & [116] \\ \(N\)-Feruloylserotonin (**256**) & Leaves & Antimicrobial activity & [58] \\ \(N\)-Feruloyltryptamine (**257**) & Leaves & - & [116] \\ \(N\)-Zero-Mode 3-acetic acid (**258**) & Whole rice plant &
\begin{tabular}{c} Regulation on growth \\ and development \\ \end{tabular} \\ Serotonin = 5-Hydroxytryptamine (**259**) & Leaves & - & [118] \\ Tryptamine (**260**) & Leaves & - & [118] \\ \hline \hline \end{tabular}
\end{table}
Table 8: Alkaloids and their biological activities.