Effect of exogenous catechin on alleviating O3 stress: The role of catechin-quinone in lipid peroxidation, salicylic acid, chlorophyll content, and antioxidant enzymes of Zamioculcas zamiifolia.

Ozone (O3) can cause oxidative stress in plants and humans. Catechin is an antioxidant that enriches tea and can probably increase O3 tolerance in plants. To investigate the mechanism of catechin to alleviate O3 stress in plants, Zamiocalcus zamiifolia (an efficient plant for O3 phytoremediation) was sprayed with 5 mM catechin and was used to expose O3 (150-250) under long-term operation (10 cycles). We investigated whether exogenous catechin could enhance O3 removal and alleviate O3 stress through a balanced redox state in plants. Z. zamiifolia sprayed with catechin exhibited higher O3 removal (80.27±3.12%), than Z. zamiifolia without catechin (50.03±2.68%). O3 in the range of 150-250 ppb led to stress in plants, as shown by an increased malondialdehyde content (MDA) and salicylic acid (SA). Whereas under the presence of O3, exogenous catechin could maintain the MDA content and inhibit SA accumulation. Under Z. zamiifolia+catechin+O3 conditions, catechin reacted with O3, which led to the formation of catechin-quinone. The formation of catechin-quinone was confirmed by the depletion of reduced glutathione content (GSH). This catechin-quinone could induce GST and APX genes that are up-regulated approximately 35- and 5-fold, respectively. Hence, Z. zamiifolia+catechin+O3 conditions had higher performance for coping with oxidative stress than did Z. zamiifolia+O3 conditions. This evidence demonstrates that catechin could enhance O3 removal through a balanced redox state in plant cells. Finally, the application of tea extract for enhanced O3 removal is also shown in this study.

Contribution of Bacillus cereus ERBP in ozone detoxification by Zamioculcas zamiifolia plants: Effect of ascorbate peroxidase, catalase and total flavonoid contents for ozone detoxification.

Eighteen plant species were screened for ozone (O3) removal in a continuous system. Zamioculcas zamiifolia had the highest O3 removal efficiency. To enhance O3 removal by Z. zamiifolia, adding a compatible endophytic bacteria, Bacillus cereus ERBP into Z. zamiifolia was studied. After operating under an O3 continuous system (150-250 ppb) at a flow rate of 0.3 L min-1 for 80 h, inoculated plants (74%) exhibited higher O3 removal efficiency than non-inoculated ones (53%). In addition, after O3 exposure (80 h), the population of B. cereus ERBP in inoculated plants was significantly increased in both shoots approximately 35 folds and leaves 13 folds compared to inoculated plants without O3 exposure. The results also showed that B. cereus ERBP had the ability to protect Z. zamiifolia against O3 stress conditions. The increase in B. cereus ERBP populations was attributed to the significant increase in ascorbate peroxidase (APX) and catalase (CAT) activity. In addition, increasing B. cereus ERBP populations led to raise total flavonoid contents which is one of antioxidant compounds. Increasing APX, CAT activities, and total flavonoid contents can enhance O3 detoxification in plant tissues. The mechanism of B. cereus ERBP for enhancing O3 phytoremediation was proposed in this study. The results suggested that B. cereus ERBP was a potential tool for alleviating O3 stress on Z. zamiifolia and enhancing O3 phytoremediation efficiency.