Functional Analysis of Polyphenol Oxidases by Antisense/Sense Technology

Abstract

Polyphenol oxidases (PPOs) catalyze the oxidation of phenolics to quinones, the secondary reactions of which lead to oxidative browning and postharvest losses of many fruits and vegetables. PPOs are ubiquitous in angiosperms, are inducible by both biotic and abiotic stresses, and have been implicated in several physiological processes including plant defense against pathogens and insects, the Mehler reaction, photoreduction of molecular oxygen by PSI, regulation of plastidic oxygen levels, aurone biosynthesis and the phenylpropanoid pathway. Here we review experiments in which the roles of PPO in disease and insect resistance as well as in the Mehler reaction were investigated using transgenic tomato (Lycopersicon esculentum) plants with modified PPO expression levels (suppressed PPO and overexpressing PPO). These transgenic plants showed normal growth, development and reproduction under laboratory, growth chamber and greenhouse conditions. Antisense PPO expression dramatically increased susceptibility while PPO overexpression increased resistance of tomato plants to Pseudomonas syringae. Similarly, PPO-overexpressing transgenic plants showed an increase in resistance to various insects, including common cutworm (Spodoptera litura (F.)), cotton bollworm (Helicoverpa armigera (Hübner)) and beet army worm (Spodoptera exigua (Hübner)), whereas larvae feeding on plants with suppressed PPO activity had higher larval growth rates and Molecules 2007, 12 1570 consumed more foliage. Similar increases in weight gain, foliage consumption, and survival were also observed with Colorado potato beetles (Leptinotarsa decemlineata (Say)) feeding on antisense PPO transgenic tomatoes. The putative defensive mechanisms conferred by PPO and its interaction with other defense proteins are discussed. In addition, transgenic plants with suppressed PPO exhibited more favorable water relations and decreased photoinhibition compared to nontransformed controls and transgenic plants overexpressing PPO, suggesting that PPO may have a role in the development of plant water stress and potential for photoinhibition and photooxidative damage that may be unrelated to any effects on the Mehler reaction. These results substantiate the defensive role of PPO and suggest that manipulation of PPO activity in specific tissues has the potential to provide broad-spectrum resistance simultaneously to both disease and insect pests, however, effects of PPO on postharvest quality as well as water stress physiology should also be considered. In addition to the functional analysis of tomato PPO, the application of antisense/sense technology to decipher the functions of PPO in other plant species as well as for commercial uses are discussed.

Effects of cadmium on growth and antioxidant responses in Glycyrrhiza uralensis seedlings

“…It could catalyze the oxidization of such a group of compounds as phenol to quinone. PPO and POD relate closely with 'the callus reaction' , meanwhile, they also have some relationships with the synthesis of cell compounds containing phenol groups such as lignin (Thipyapong et al 2007). As shown in Figure 6, the total PPO activity in licorice plants increased significantly exposed to cadmium stress.…”

“…However, the activity decreased significantly at 0.2 and 0.4 mmol/l cadmium concentrations, representing 24.2% and 33.3% decrease, respectively. Previous reports showed that rapid changes in PPO activity were proposed that may be involved in necrosis development around damaged leaf surfaces and in defense mechanisms against insects and plant pathogen attack (Thipyapong et al 2007). PPO activity in some plant species was observed under heavy metal stress, and showed a significant increase compared to the control Klejdus 2008, Saffar et al 2009).…”

Herbivore exploits orally secreted bacteria to suppress plant defenses

“…To investigate if microbial symbionts present in OSs affect induced defenses, we measured the expression of selected defense genes and enzymatic activities in plants damaged by AB-treated or untreated larvae. The cysteine proteinase inhibitor (CysPI) and polyphenol oxidase F/B (PPOF/B) were selected as JA-marker genes because they are well-established JA-inducible proteins that function against CPBs (19)(20)(21). For an SA-marker gene, pathogenesis-related 1 (PR-1(P4)) was selected (22).…”

Isolation and properties of polyphenol oxidase from basidiocarps of Lactarius pergamenus Fr. (Fr.) fungi

“…It is proved that o-quinones formed by the enzymatic action protect plants against pathogens and insects. Melanin formed by action of fungi PPO causes sporulation and is involved in fungi virulence [3][4][5]. PPO activity in basidiomycota fungi has specific characteristics.…”