Resting cysts represent the dormant life stage produced by sexual reproduction of dinoflagellates; it generally maintain a limited level of metabolic activities. In the present study, changes in the photosynthetic apparatus of Akashiwo sanguinea during the encystment process in different nitrogen (N) conditions were characterized, and the transcriptional responses of nine photosynthesis genes were further evaluated. The photochemical efficiency decreased with elevation of N deprivation and growth of algae, and the resting cysts maintained limited photosynthetic activity. Meanwhile, the transcription of photosystem II genes (psbA and psbD) were down-regulated, especially the levels of the psbA gene, suggesting the inactivation of photosystem II under N limitation. Moreover, genes involved in cytochrome f (petA) and ATP synthase (atpA, atpB) were also transcribed at low levels in N-deprivation cultures. In contrast, the transcription of the RubisCO large subunit gene (rbcL) was up-regulated, indicating the maintenance of carbon fixation in N-limited conditions. The transcription levels of photosystem I genes (psaA and psaB) showed no significant correlation with the N condition. Further, most of the photosynthesis genes were down-regulated in the resting cysts, which was coincided with the inactive physiological status of the dormant stage. The results demonstrated that photosynthesis genes are differentially regulated in response to varying N conditions and life cycles. The findings will provide fundamental knowledge for better understanding the physiological characteristics and molecular regulation mechanisms in the developmental life cycle of marine dinoflagellates.

中文翻译：

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赤石窝鞭毛藻静息囊肿形成过程中光合活性的变化

静息囊肿代表由甲藻有性繁殖产生的休眠生命阶段；它通常维持有限水平的代谢活动。在本研究中，对不同氮 (N) 条件下，赤石窝 sanguinea 成囊过程中光合装置的变化进行了表征，并进一步评估了 9 个光合作用基因的转录反应。光化学效率随着 N 剥夺的增加和藻类的生长而降低，并且静止的孢囊保持有限的光合活性。同时，光系统II基因（psbA和psbD）的转录被下调，尤其是psbA基因的水平，表明光系统II在N限制下失活。此外，与细胞色素 f (petA) 和 ATP 合酶 (atpA, atpB) 在 N 剥夺培养中也以低水平转录。相比之下，RubisCO 大亚基基因 (rbcL) 的转录上调，表明在 N 限制条件下维持碳固定。光系统 I 基因（psaA 和 psaB）的转录水平与 N 条件没有显着相关性。此外，大多数光合作用基因在休眠包囊中下调，这与休眠期的不活跃生理状态相吻合。结果表明，光合作用基因响应于不同的氮条件和生命周期而受到差异调节。这些发现将为更好地理解海洋甲藻发育生命周期的生理特征和分子调控机制提供基础知识。