Department of Plant Biology and Ecology, University of Basque Country (UPV/EHU), ES-48080 Bilbao, Spain.
Physiol Plant. 2010 Sep 1;140(1):69-78. doi: 10.1111/j.1399-3054.2010.01385.x. Epub 2010 May 8.
Leaves are the main photosynthetically active tissues in most plants. However, stems and fruits are also important for the overall carbon balance of the plant because of their contribution to fixation of the CO(2) released by respiration. Photosynthesis could not be possible without a complete set of photoprotection mechanisms, which include the ubiquitous violaxanthin (V) cycle and the taxonomically restricted lutein epoxide (Lx) cycle. In this work, we characterise carotenoid stoichiometry in photosynthetic stems and fruits of avocado in comparison with that of leaves and specifically whether Lx is present in these tissues and also whether it is involved in a light-driven cycle. Avocado was selected as model species to study whether both cycles were functional in non-foliar photosynthetic structures (stems and fruits). An unusual pigment composition was observed in avocado fruit, with a high content of cis-V and cis-Lx, suggesting a different photosynthetic function. In stems, both xanthophylls de-epoxidated upon illumination, but only V recovered in the dark, indicating the existence of a possible 'truncated' Lx cycle. Lx in fruits was de-epoxidated only when its pool was higher than a threshold of 30 mmol mol(-1) chlorophyll, indicating a high non-photoconvertible pool of Lx. We conclude that, at least in stems, the dynamic regulation of photosynthetic activity could also depend on the Lx cycle.
叶子是大多数植物中主要的光合作用活跃组织。然而，茎和果实对于植物的整体碳平衡也很重要，因为它们有助于固定呼吸作用释放的 CO2。如果没有一套完整的光保护机制，光合作用是不可能进行的，这些机制包括普遍存在的紫黄质（V）循环和分类上受限的叶黄素环氧化合物（Lx）循环。在这项工作中，我们比较了鳄梨光合作用茎和果实中的类胡萝卜素化学计量与叶片中的类胡萝卜素化学计量，特别是 Lx 是否存在于这些组织中，以及它是否参与光驱动循环。选择鳄梨作为模型物种来研究两个循环是否在非叶光合作用结构（茎和果实）中起作用。在鳄梨果实中观察到一种不寻常的色素组成，具有高含量的顺式-V 和顺式-Lx，表明具有不同的光合作用功能。在茎中，两种叶黄素在光照下都去环氧化，但只有 V 在黑暗中恢复，表明存在可能的“截断”Lx 循环。只有当 Lx 池高于叶绿素 30 mmol mol(-1)的阈值时，果实中的 Lx 才会去环氧化，表明 Lx 有很大一部分是非光转化的。我们得出结论，至少在茎中，光合作用活性的动态调节也可能依赖于 Lx 循环。
