Abstract
High-quality green tea is produced from buds and young leaves grown by the covering-culture method, which employs shading treatment for tea plants (Camellia sinensis L.). Shading treatment improves the quality of tea, but shaded tea plants undergo sudden exposures to high light (HL) at the end of the treatment by shade removal. In this study, the stress response of shaded tea plants to HL illumination was examined in field condition. Chl a/b ratio was lower in shaded plants than nonshaded control, but it increased due to exposure to HL after 14 days. Rapid decline in Fv/Fm values and increases in carbonylated protein level were induced by HL illumination in the shaded leaves on the first day, and they recovered thereafter between a period of one and two weeks. These results revealed that shaded tea plants temporarily suffered from oxidative damages caused by HL exposure, but they could also recover from these damages in 2 weeks. The activities of antioxidant enzymes, total ascorbate level, and ascorbate/dehydroascorbate ratio were decreased and increased in response to low light and HL conditions, respectively, suggesting that the upregulation of antioxidant defense systems plays a role in the protection of the shaded tea plants from HL stress.
Highlights
The tea plant (Camellia sinensis (L.) O
The number, length, and weight of shoots decreased in the fall season of 2012, which eventually resulted in decreased yield, and the number of shoots and yield decreased in the first cropping season in 2013 [12], indicating the negative impact of consecutive shade treatments after the second cropping season in the second year
In order to examine the effects of high light (HL) illumination after shading treatment, we monitored the physiological changes of shaded tea plants for 14 days after shade removal in the first and the second cropping season of 2012
Summary
The tea plant (Camellia sinensis (L.) O. Kuntze) is an important commercial beverage crop cultivated worldwide. Its apical buds and young leaves are harvested and used for producing tea. The quality of the produced tea is affected by various metabolites that contribute to its taste and flavor. Those compounds include amino acids, theanine, and catechins that provide tea with good and astringent taste, respectively [1,2]. Catechins possess antioxidant and anticancer activities [3], thereby providing the tea with beneficial effects on human health; theanine produces a relaxing and an arousal effect by increasing alpha-band activity in the human brain [4]
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