The function of plastids in the deep-sea benthic foraminifer, Nonionella stella
The function of plastids in the deep-sea benthic foraminifer, Nonionella stella
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DOI：
10.4319/lo.2002.47.6.1569
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发表时间：
2002-11-01
影响因子：
4.5
通讯作者：
Bernhard, JM
中科院分区：
文献类型：
--
作者：
Grzymski, J;Schofield, OM;Bernhard, JM
奇怪的是，在加州附近约600米深的沉积物上层3厘米处发现的底栖有孔虫，Nonionella stella，保留了叶绿体。我们研究了宿主细胞内细胞器的起源和生理功能。透射电子显微镜，荧光和吸收光谱，蛋白质印迹，和酶的测定表明，叶绿体是完整的，并保留功能长达1年后，样品收集。16S rDNA基因序列分析表明，这些质体来源于与中肋骨条藻和中华齿藻亲缘关系较近的硅藻。三个主要的叶绿体蛋白质（核酮糖二磷酸羧化酶加氧酶[RuBisCO]，D1蛋白，和岩藻黄素叶绿素a蛋白复合物）的Western印迹证实，细胞器保留核和叶绿体编码的蛋白质，这表明质体机器的营业额非常低。此外，两个羧化酶检查，RuBisCO和磷酸烯醇丙酮酸羧化酶，保留催化活性。关于深海有孔虫隔离叶绿体功能的三种假设被认为是：（1）细胞器在极低的辐照水平下进行光合作用，（2）细胞器利用外源底物产生电化学梯度，允许在黑暗中进行化学自养，（3）它们用于无机氮的同化。我们的研究结果表明，叶绿体用于满足宿主的氮需求。核编码的蛋白质，硝酸还原酶的免疫定位，支持这一假设。这种蛋白质广泛分布于光合自养生物中，但在真核原生生物如有孔虫中不编码。
Curiously, the benthic foraminifer, Nonionella stella, found in the upper 3 cm of sediments collected off California at a depth of similar to600 m, retains chloroplasts. We examined the origin and physiological function of the organelles within the host cell. Transmission electron micrographs, fluorescence and absorption spectra, Western blots, and enzyme assays revealed that the chloroplasts were intact and retained functionality for up to 1 year after sample collection. 16S rDNA gene sequences established that the plastids were derived from diatoms closely related to Skeletonema costatum and Odontella sinensis. Western blots of three major chloroplast proteins (ribulose bis-phosphate carboxylase oxygenase [RuBisCO], the D1 protein, and the fucoxanthin chlorophyll a protein complex) confirmed that the organelle retained both nuclear and chloroplast encoded proteins, which suggests that the turnover of the plastid machinery is extremely low. Moreover, the two carboxylating enzymes examined, RuBisCO and phosphoenol pyruvate carboxylase, retained catalytic activity. Three hypotheses regarding the function of sequestered chloroplasts in deep-sea foraminifera were considered: (1) the organelles are photosynthetic under extremely low irradiance levels, (2) the organelles utilize exogenous substrates to generate an electrochemical gradient that permits chemoautrophy in the dark, and (3) they are used for the assimilation of inorganic nitrogen. Our results suggest that the chloroplasts are used to meet the nitrogen requirements of the host. Immunolocalization of the nuclear encoded protein, nitrate reductase, supports this hypothesis. This protein is widely distributed in photoautotrophs but is not encoded in eukaryotic protists such as foraminifera.