Kleptoplastidic, or chloroplast-stealing, lineages offer insight into the process of acquiring photosynthesis. By quantifying the ability of these organisms to retain and use photosynthetic machinery from their prey, we can understand how intermediaries on the endosymbiosis pathway might have evolved regulatory and maintenance mechanisms. Here, we focus on a mixotrophic kleptoplastidic ciliate, Mesodinium chamaeleon, noteworthy for its ability to retain functional chloroplasts from at least half a dozen cryptophyte algal genera. We contrasted the performance of kleptoplastids from blue-green and red cryptophyte prey as a function of light level and feeding history. Our experiments showed that starved M. chamaeleon cells are able to maintain photosynthetic function for at least 2 weeks and that M. chamaeleon containing red plastids lost chlorophyll and electron transport capacity faster than those containing blue-green plastids. However, likely due to increased pigment content and photosynthetic rates in red plastids, M. chamaeleon had higher growth rates and more prolonged growth when feeding on red cryptophytes. For example, M. chamaeleon grew rapidly and extensively when fed the blue-green cryptophyte Chroomonas mesostigmatica, but this growth appeared to hinge on high levels of feeding supporting photosynthetic activity. In contrast, even starved M. chamaeleon containing red plastids from Rhodomonas salina could achieve high photosynthetic rates and extensive growth. Our findings show that plastid origin impacts the maintenance and magnitude of photosynthetic activity, though whether this is due to variation in ciliate control or gradual loss of plastid function in ingested prey cells remains unknown.

中文翻译：

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猎物类型限制了 kleptoplastidic 纤毛虫 Mesodinium chamaeleon (Ciliophora) 的生长和光合能力

Kleptoplastidic 或叶绿体窃取谱系提供了对获得光合作用过程的洞察。通过量化这些生物保留和利用猎物的光合作用机制的能力，我们可以了解内共生途径上的中介如何进化调节和维持机制。在这里，我们专注于一种混合营养的 kleptoplastidic 纤毛虫 Mesodinium chamaeleon，值得注意的是它能够保留来自至少六种隐藻藻属的功能性叶绿体。我们将来自蓝绿色和红色隐生植物猎物的 kleptoplastids 的性能作为光照水平和摄食历史的函数进行了对比。我们的实验表明，饥饿的变色龙细胞能够保持光合作用功能至少 2 周，并且含有红色质体的变色龙比含有蓝绿色质体的变色龙失去叶绿素和电子传输能力的速度更快。然而，可能是由于红色质体中色素含量和光合速率的增加，变色龙在以红色隐生植物为食时具有更高的生长速率和更长的生长时间。例如，M.蜓座供给的蓝绿色cryptophyte时迅速而广泛地增长蓝隐mesostigmatica，但这种增长似乎取决于对高水平喂养支撑光合活性。相比之下，即使饥饿的变色龙含有红色质体Rhodomonas salina可以实现高光合速率和粗放生长。我们的研究结果表明，质体起源影响光合作用活动的维持和大小，尽管这是否是由于纤毛虫控制的变化或摄入的猎物细胞中质体功能的逐渐丧失仍然未知。