Pyropia haitanensis has a typical parthenogenetic behavior under unisexual culture condition. In this study, ultrastructural evolution and physiological traits of photosynthesis and the expression characteristics of key enzyme genes related to carbon and nitrogen assimilation pathways at different developmental stages of parthenogenesis were analyzed. Ultrastructural observations showed that the gametophytic vegetative cells had cell wall, pyrenoids, abundant chloroplasts, and rarely scattered floridean starch grains. However, the appearance of gathered chloroplasts, plastoglobuli, large lipid droplets, pyrenoids encircled by numerous plastoglobuli, and an increased number of floridean starch grains in the cells during parthenogenesis provide neutral lipid and energy resources that are compatible with the developmental transitions. Physiologically, vegetative gametophytes possessed the highest F_v/F_m and Chl. a content and the lowest C/N ratio. However, compared with vegetative cell proliferation stage, the activities of RubisCO (ribulose bisphosphate carboxylase) and external CA (carbonic anhydrase) increased at early stages of parthenogenesis, and F_v/F_m and activities of PEPC (phosphoenolpyruvate carboxylase) and PEPCK (phosphoenolpyruvate carboxykinase) remained higher at later stages of parthenogenesis, suggesting that dynamic photosynthetic carbon fixation occurs in parthenogenesis. Quantitative real-time PCR analysis showed that selective regulation of key enzyme genes related to carbon and nitrogen assimilation pathways maintained stable carbon and nitrogen metabolism during developmental transitions of parthenogenesis. Moreover, during parthenogenesis, photosynthetic carbon fixation pathway potentially changed from C₃ pathway at female gametophyte stage to C₄ pathway at parthenosporophyte stage, which is similar to that of gametophytes and sporophytes in sexual reproduction. Meanwhile, the ammonia assimilation involved GDH pathway (glutamate dehydrogenase pathway) and GS/GOGAT cycle (glutamine synthetase/glutamate synthase cycle) in female gametophyte stage, while GS/GOGAT cycle was dominant in parthenosporophyte stage, suggesting that GS/GOGAT cycle may play an important role in the carbon and nitrogen balance during the developmental transitions of parthenogenesis. These results provide important information for revealing the adaptation strategy of parthenogenesis in Pyropia.

海坛紫罗兰在单性文化条件下具有典型的孤雌生殖行为。本研究分析了单性生殖不同发育阶段光合作用的超微结构演变和生理特性，以及与碳和氮同化途径相关的关键酶基因的表达特征。超微结构观察表明，配子体营养细胞具有细胞壁，类胡萝卜素，丰富的叶绿体，很少散布弗洛里丹淀粉粒。然而，在孤雌生殖过程中细胞中聚集的叶绿体，质球体，大脂质滴，被许多质体球包围的类胡萝卜素的出现以及在细胞中单性发生时增加的弗洛里丹淀粉颗粒的数量提供了与发育过渡相容的中性脂质和能源。在生理上F _v / F _m和Chl。一内容和最低C / N比。然而，与无性繁殖阶段相比，孤雌生殖的早期RubisCO（核糖双磷酸羧化酶）和外部CA（碳酸酐酶）的活性增加，F _v / F _m在孤雌生殖的后期阶段，PEPC（磷酸烯醇丙酮酸羧化酶）和PEPCK（磷酸烯醇丙酮酸羧化酶）的活性仍然较高，这表明在孤雌生殖中发生了动态光合碳固定。实时定量PCR分析表明，在孤雌生殖的发育过渡过程中，与碳和氮同化途径有关的关键酶基因的选择性调节保持了稳定的碳和氮代谢。此外，在孤雌生殖过程中，光合作用的碳固定路径可能从雌配子体阶段的C ₃路径变为C _4。单性孢子体阶段的途径，与配子体和子孢子体在有性生殖中的相似。同时，在雌配子体阶段氨同化作用涉及GDH途径（谷氨酸脱氢酶途径）和GS / GOGAT循环（谷氨酰胺合成酶/谷氨酸合酶循环），而GS / GOGAT循环在单性孢子体阶段占主导地位，表明GS / GOGAT循环可能发挥作用。在孤雌生殖的发育过渡过程中，碳和氮平衡起着重要作用。这些结果为揭示远视孤雌生殖的适应策略提供了重要信息。