Department of Life Sciences and Biotechnologies, University of Ferrara, C.so Ercole I d'Este 32, 44121 Ferrara, Italy.
Plant Physiol Biochem. 2013 Feb;63:140-50. doi: 10.1016/j.plaphy.2012.11.023. Epub 2012 Dec 5.
The low photosynthetic activity of fleshy green fruits is currently attributed to their special anatomy rather than to a down-regulation of photosystem II (PSII). However, it is unclear whether the organization of PSII, which is highly conserved in leaves, is also shared by non-foliar structures, such as fleshy fruits. To obtain new information on this aspect, the photosynthetic activity and the organization of PSII were investigated in the berry of Arum italicum Miller during maturation (ivory to green) and early ripening (green to yellow). The berry developed an "internal CO(2) recycling" photosynthesis; gross photosynthesis at the green stage was 25% of the leaf lamina. SDS-PAGE, BN-PAGE and 77 K spectrofluorimetry showed that the thylakoid membrane accumulated a very high amount of free LHCII trimers and only few PSII and PSI complexes. The pattern of PSII forms was similar to that of the lamina (monomers, dimers, LHCII-PSII supercomplexes), but increase in CP43-less PSII cores and low F695/F680 fluorescence ratio at room temperature indicated that PSII was less stable than in the leaf lamina. Beside effective PSII photoprotection, we propose that LHCII serves as a temporary storage of chlorophylls to provide a visual signal that fruit is not mature for seed dispersal. We conclude that the low photosynthetic activity of A. italicum berry depends on the scantiness of reaction centres and the reduced functionality of PSII.
肉质绿色果实的光合活性低，目前归因于其特殊的解剖结构，而不是光系统 II（PSII）的下调。然而，PSII 的组织在叶子中高度保守，是否也存在于非叶状结构中，如肉质果实，目前尚不清楚。为了获得这方面的新信息，在 Arum italicum Miller 浆果的成熟过程中（象牙色到绿色）和早期成熟过程中（绿色到黄色）研究了光合作用和 PSII 的组织。浆果发育出一种“内部 CO2 再循环”光合作用；绿色阶段的总光合作用是叶片的 25%。SDS-PAGE、BN-PAGE 和 77 K 荧光光谱法表明，类囊体膜积累了大量游离 LHCII 三聚体，只有少量 PSII 和 PSI 复合物。PSII 形式的模式与叶片相似（单体、二聚体、LHCII-PSII 超复合物），但 CP43 缺失 PSII 核心的增加和室温下低的 F695/F680 荧光比表明 PSII 不如叶片类囊体膜稳定。除了有效的 PSII 光保护外，我们还提出 LHCII 作为叶绿素的临时储存库，提供果实未成熟以进行种子散布的视觉信号。我们得出结论，A. italicum 浆果的低光合作用活性取决于反应中心的稀少和 PSII 的功能降低。
