PDF(Pubmed)
Abstract：
Photosynthetic carbon (C) fixation by phytoplankton in the Southern Ocean (SO) plays a critical role in regulating air-sea exchange of carbon dioxide and thus global climate. In the SO, photosynthesis (PS) is often constrained by low iron, low temperatures, and low but highly variable light intensities. Recently, proton-pumping rhodopsins (PPRs) were identified in marine phytoplankton, providing an alternate iron-free, light-driven source of cellular energy. These proteins pump protons across cellular membranes through light absorption by the chromophore retinal, and the resulting pH energy gradient can then be used for active membrane transport or for synthesis of adenosine triphosphate. Here, we show that PPR is pervasive in Antarctic phytoplankton, especially in iron-limited regions. In a model SO diatom, we found that it was localized to the vacuolar membrane, making the vacuole a putative alternative phototrophic organelle for light-driven production of cellular energy. Unlike photosynthetic C fixation, which decreases substantially at colder temperatures, the proton transport activity of PPR was unaffected by decreasing temperature. Cellular PPR levels in cultured SO diatoms increased with decreasing iron concentrations and energy production from PPR photochemistry could substantially augment that of PS, especially under high light intensities, where PS is often photoinhibited. PPR gene expression and high retinal concentrations in phytoplankton in SO waters support its widespread use in polar environments. PPRs are an important adaptation of SO phytoplankton to growth and survival in their cold, iron-limited, and variable light environment.
摘要：
南大洋（SO）浮游植物对光合碳（C）的固定作用在调节二氧化碳的海气交换以及全球气候中起着至关重要的作用。在SO中，光合作用(PS)通常受到低铁的限制，低温,和低但高度可变的光强度。最近,在海洋浮游植物中鉴定出质子泵浦视紫质（PPRs），提供另一种无铁，光驱动的细胞能源。这些蛋白质通过视网膜发色团的光吸收将质子泵过细胞膜，然后可以将所得的pH能量梯度用于活性膜运输或用于合成三磷酸腺苷。这里,我们表明PPR在南极浮游植物中普遍存在，特别是在铁有限的地区。在SO硅藻模型中，我们发现它位于液泡膜上，使液泡成为光驱动细胞能量产生的推定的替代光养细胞器。与光合C固定不同，在较冷的温度下大大降低，PPR的质子传输活性不受温度降低的影响。培养的SO硅藻中的细胞PPR水平随着铁浓度的降低而增加，PPR光化学产生的能量可以显着增加PS的能量，特别是在高光强度下，其中PS通常是光抑制的。SO水域浮游植物中PPR基因的表达和高视网膜浓度支持其在极地环境中的广泛使用。PPRs是SO浮游植物在寒冷中对生长和生存的重要适应，铁限制，和可变光环境。
