# Identification and Isolation Techniques for Plant Growth Inhibitors in Rice
## 3 Mechanism of Action of PGIs
### Oxidative Stress  
The action mechanism of PGIs is described in Figure 1. PGIs can induce oxidative stress in treated plants by inhibiting antioxidant enzymes, thereby enhancing reactive oxygen species (ROS) [49; 52; 53]. Consequently, oxidative damage increases, negatively affecting treated plant metabolism [49; 52; 53]. [PERSON] et al. [54] indicated that allelopathic interactions result in an imbalance between ROS and antioxidant abilities. This imbalance led to rapid protein degradation, which subsequently caused cell apoptosis or necrosis. In the research of [PERSON] et al. [40], allelochemicals inhibited the antioxidant enzymes of cucumber. In addition, membrane peroxidation was enhanced by the effects of root exudates and root extracts [40].  
\begin{table}
\begin{tabular}{l l l l l} \hline \hline \multicolumn{1}{c}{**Nodes of Action**} & \multicolumn{1}{c}{**Allelochemicals**} & \multicolumn{1}{c}{**Recipient Plant**} & \multicolumn{1}{c}{**Rice Organs**} & \multicolumn{1}{c}{**References**} \\ \hline - & Lanast-7,9(11)-dien-3\(\alpha\),15\(\alpha\)-diol-3\(\alpha\)-\(d\)-glucofuranoside & _Lemma paucicostata_ & Hulls & [42] \\ Inhibition of germination & Momilactone E (ME), & _L. sativa, E. crus-galli_, and & & \\ rate, seedling growth, & 7-ketostigmasterol (7 KS), & _Solidago altissima_ & Husks & [43] \\ shoots, and roots & MA, and MB & _Cyanobacteria_ & Straws & [44] \\ Aligicidal activities & Oleiciy-\(\beta\)-\(d\)-arabinoside & _Cyanobacteria_ & Straws & [44] \\ Inhibition of spore germination & Sakuranetin & _Pyricular origaze_ & Leaves & [45] \\ - & Two flavone \(O\)-glycos & Interferes with weeds or & Seedlings & [46] \\ \hline \multicolumn{1}{c}{**Physiological pathways**} & & & \\ Inhibition of & Caffe, coumaric, ferulic, & & & \\ photosynthesis & cinnamic, and vanillic acids & - & - & [47; 48] \\ Suppress respiration & Benzoic and cinnamic acids & - & - & [49] \\ \hline \multicolumn{1}{c}{**Enzyme functions**} & & \\ Phosphorylase suppressors & Chlorogenic, caffe acids, & - & - & [50; 51] \\  & and catechol & _E. crus-galli_ & Whole plant & [50; 51] \\ ATPase inhibitors & Cimamic acid and its & _E. crus-galli_ & Whole plant & [50; 51] \\  & derivatives & & & \\ \hline \multicolumn{1}{c}{**Rhizosphere microorganisms**} & & & \\ Suppression of nitrification & & & & \\ process, by inhibiting the & Methyl & & \\ activities of vital enzymes & 3-(4-hydroxyphenyl) & & Whole plant, root & \\ such as ammonium & propionate, linoleic acid, & - & exudates & [6] \\ mono-oxygenase and & methyl-\(p\)-coumarate and & & & \\ hydroxylamine & methyl ferulate & & & \\ oxidoreductase & & & & \\ Inhibition of the oxidation & Caffe and ferulic acids, & & & \\ myriacetin, tannins and & - & - & [12] \\ of NH 4+ to NO2- & tannin derivatives & & & \\ Synergistic suppressive & & & Decomposition of & \\ effect by reducing & Different phenolic & Rhizobium strain & rice residue and & [6] \\ nitrogen-fixing ability & & & & straw in soil & \\  & Tricin (5,7,4\({}^{\prime}\)-trihydroxy- & & & \\ Affecting soil community & 3\({}^{\prime}\),5\({}^{\prime}\)-dimethoxyflavone) & & & \\ structure and reducing & and aurone isomer & _Fusarium oxysporum_ and & Hulls, leaves, roots, & \\ fungi present in paddy soil & (5,7,4\({}^{\prime}\)-trihydroxy-3\({}^{\prime}\),5\({}^{\prime}\)- & & \\ dimethoxyanurone) of & & & \\ tricin & & & \\ \hline \multicolumn{1}{c}{**Pathogen infection**} & & & \\ Suppressing Xoo growth in & (S)-Limonene, oryallides A & _Xanthomonas oryzae_ & Seedlings and & \\ rice seedlings & and B, and oryzalc acid A & _Fusarium oxysporum_ and & Hulls, leaves, roots, & \\ \hline \hline \end{tabular}
\end{table}
Table 1: _Cont._