Antinutritive plant defence mechanisms

Chemical Defence and Toxins of Plants

“…Oxidative enzymes such as polyphenol oxidases (PPO) and peroxidases (POD) oxidize phenolics, monophenols, and diphenols into reactive molecular species such as quinones and quinone methides, which covalently bind to nucleophilic residues in dietary proteins such as -SH, -NH 2 residues of nutritionally important amino acids such as cysteine and lysine, thereby decreasing the nutritive values of dietary proteins (Figure 7). 55 4.08.1.2.1(vii) Terpenoids Terpenoids are chemicals that basically consist of isoprene (C5) units. Despite this similarity in basic units, terpenoids are extremely diverse in their structures and biological activities and include a large number of chemicals; at least 15 000 terpenoids are found in plants.…”

“…55,77,78 Serine proteinase inhibitors inhibit serine proteinases such as trypsin and chymotrypsin, the major digestive proteinases in lepidopteran and a part of coleopteran insects, and many of which are classified into Bowman-Birk inhibitors and Kunitz inhibitors according to the structures, but some, such as potato inhibitors, are not included in these classes. 77 Serine proteinase inhibitors are most abundant in storage tissues such as seeds and tubers, and their concentrations reach a few percent of the total protein.…”

“…84 Seed weevils utilize cysteine proteinases (CPs) instead of serine proteinases as their digestive proteinase, which enables seed weevils to feed on beans rich in serine proteinase inhibitors. 55 …”

“…87 4.08.1.2.2(iv) Polyphenol oxidases and peroxidase Polyphenol oxidases (PPO), which occur in many plants together with phenolics, catalyze the oxidation of mono-, di-, and polyhydric phenols to quinones. 55 Quinones formed by these reactions are active and covalently bind to nucleophilic side chains (-SH, -NH 2 , TNH) of proteins and, as a result, lysine, histidine, cysteine, and methionine are lost from dietary proteins and the nutritive value of the protein is significantly reduced (Figure 7). 55,88 POD also catalyze the oxidation of phenolics and, as a result, oxidation products such as quinone and quinone methides are formed.…”

“…55 Quinones formed by these reactions are active and covalently bind to nucleophilic side chains (-SH, -NH 2 , TNH) of proteins and, as a result, lysine, histidine, cysteine, and methionine are lost from dietary proteins and the nutritive value of the protein is significantly reduced (Figure 7). 55,88 POD also catalyze the oxidation of phenolics and, as a result, oxidation products such as quinone and quinone methides are formed. These oxidation products also covalently bind to side chains of amino acids such as lysine and cysteine52 ( Figure 7).…”