Carotenoids are essential components of the photosynthetic apparatus involved in plant photoprotection. To investigate the protective role of zeaxanthin under high light and UV stress we have increased the capacity for its biosynthesis in tobacco plants (Nicotiana tabacum L. cv. Samsun) by transformation with a heterologous carotenoid gene encoding beta-carotene hydroxylase (crtZ) from Erwinia uredovora under constitutive promoter control. This enzyme is responsible for the conversion of beta-carotene into zeaxanthin. Although the total pigment content of the transgenics was similar to control plants, the transformants synthesized zeaxanthin more rapidly and in larger quantities than controls upon transfer to high-intensity white light. Low-light-adapted tobacco plants were shown to be susceptible to UV exposure and therefore chosen for comparative analysis of wild-type and transgenics. Overall effects of UV irradiation were studied by measuring bioproductivity and pigment content. The UV exposed transformed plants maintained a higher biomass and a greater amount of photosynthetic pigments than controls. For revelation of direct effects, photosynthesis, pigment composition and chlorophyll fluorescence were examined immediately after UV treatment. Low-light-adapted plants of the crtZ transgenics showed less reduction in photosynthetic oxygen evolution and had higher chlorophyll fluorescence levels in comparison to control plants. After 1 h of high-light pre-illumination and subsequent UV exposure a greater amount of xanthophyll cycle pigments was retained in the transformants. In addition, the transgenic plants suffered less lipid peroxidation than the wild-type after treatment with the singlet-oxygen generator rose bengal. Our results indicate that an enhancement of zeaxanthin formation in the presence of a functional xanthophyll cycle contributes to UV stress protection and prevention of UV damage.

中文翻译：

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细菌胡萝卜素羟化酶基因（crtZ）的表达增强了烟草的紫外线耐受性。

类胡萝卜素是参与植物光保护的光合作用设备的重要组成部分。为了研究玉米黄质在强光和紫外线胁迫下的保护作用，我们通过转化编码欧文氏菌β-胡萝卜素羟化酶（crtZ）的异源类胡萝卜素基因，提高了玉米黄质在烟草植物（Nicotiana tabacum L.cv.Samsun）中的生物合成能力。组成型启动子控制下的uredovora。该酶负责将β-胡萝卜素转化为玉米黄质。尽管转基因植物的总色素含量与对照植物相似，但是在转移至高强度白光时，转化体比对照更快速且大量地合成玉米黄质。已证明适应低光照的烟草植物容易受到紫外线的照射，因此被选择用于野生型和转基因植物的比较分析。通过测量生物生产力和色素含量研究了紫外线辐射的总体效果。与对照相比，暴露于紫外线的转化植物保持更高的生物量和更多的光合色素。为了揭示直接效果，紫外线处理后立即检查了光合作用，色素组成和叶绿素荧光。与对照植物相比，低光照适应性crtZ转基因植物显示出更少的光合氧气释放减少，叶绿素荧光水平更高。经过1 h的高光预照明和随后的紫外线照射后，大量的叶黄素循环色素保留在转化体中。此外，用单线态氧发生器玫瑰红孟加拉国处理后，转基因植物的脂质过氧化程度低于野生型。我们的结果表明，在功能性叶黄素循环的存在下，玉米黄质形成的增强有助于紫外线胁迫的保护和防止紫外线的损害。