17:15 〜 19:15
[BCG07-P04] Responses of the “naked” foraminifer Allogromia laticollaris to environmental changes based on cell observations
キーワード：有孔虫、環境適応、細胞動態、カロテノイド合成
Benthic foraminifers inhabit a wide range of marine environments from intertidal zones to deep seafloor. The genus Allogromia, a widespread monothalamous group, is physiologically capable of adapting to various environments such as temperature, light, and dissolved oxygen. Allogromia species have reddish cytoplasm due to synthesis of carotenoids in their cells instead of precipitation of biomineral test. The lack of a test has enabled us to work on nuclear and genomic dynamics of Allogromia species through cell observations. However, their cell dynamics associating with environmental conditions remain poorly understood. This study examined the cell and nuclear dynamics of Allogromia laticollaris, a culture strain, under different light conditions based on cell observations to assess their environmental adaptability in a wide range of marine environments.
We firstly captured the fundamental cell morphology and the lifecycle of A. laticollaris by inverted microscopy observations and observed the nuclear morphology with the fluorescent probe Hoechst 33342. Each of 24 individuals was cultured with three different light conditions: light for 24 hours, dark for 24 h, and light / dark in 12h cycle as a control, for 19 weeks. Cell diameter and area of an individual were measured to evaluate growth amount and rates among the three conditions. A. laticollaris individuals had basically sphere shape but showed irregular shape by elongating pseudopodia to catch foods. The number of nuclei was different from a single to 10 nuclei depending on individuals. The position of nuclei was shifted accompanying with cell elongation. The cell size was increasing five-fold more in the lifecycle, though this size decreased in ~40% with starvation condition. Thus, A. laticollaris cell size could be corresponded to stress conditions. The cell size of individuals in 24 h light was significantly smaller than those of two other light conditions, indicating the constant light state provides stress to foraminifers. On the other hand, the cell size of individuals in 24 h dark was significantly larger than those of two other light conditions. Moreover, the reddish color of cytoplasm was bright in 24 h light, whereas was dark in 24 h dark. These results suggest that foraminifers synthesize carotenoid for photoprotection at the expense of cell growth. In both conditions with 24 h light and 24 h dark, the mortality rates of individuals was higher than those of control. Even with short life in the 24 h light condition, some individuals were reproduced. The light stress inhibits cell growth of foraminifers and shortens their lifespan, probably due to oversynthesis of carotenoid. However, they accelerate reproduction timing owing to maintain the lineage. A. laticollaris employs unique adaptive strategies to cope with light stress environments.
We firstly captured the fundamental cell morphology and the lifecycle of A. laticollaris by inverted microscopy observations and observed the nuclear morphology with the fluorescent probe Hoechst 33342. Each of 24 individuals was cultured with three different light conditions: light for 24 hours, dark for 24 h, and light / dark in 12h cycle as a control, for 19 weeks. Cell diameter and area of an individual were measured to evaluate growth amount and rates among the three conditions. A. laticollaris individuals had basically sphere shape but showed irregular shape by elongating pseudopodia to catch foods. The number of nuclei was different from a single to 10 nuclei depending on individuals. The position of nuclei was shifted accompanying with cell elongation. The cell size was increasing five-fold more in the lifecycle, though this size decreased in ~40% with starvation condition. Thus, A. laticollaris cell size could be corresponded to stress conditions. The cell size of individuals in 24 h light was significantly smaller than those of two other light conditions, indicating the constant light state provides stress to foraminifers. On the other hand, the cell size of individuals in 24 h dark was significantly larger than those of two other light conditions. Moreover, the reddish color of cytoplasm was bright in 24 h light, whereas was dark in 24 h dark. These results suggest that foraminifers synthesize carotenoid for photoprotection at the expense of cell growth. In both conditions with 24 h light and 24 h dark, the mortality rates of individuals was higher than those of control. Even with short life in the 24 h light condition, some individuals were reproduced. The light stress inhibits cell growth of foraminifers and shortens their lifespan, probably due to oversynthesis of carotenoid. However, they accelerate reproduction timing owing to maintain the lineage. A. laticollaris employs unique adaptive strategies to cope with light stress environments.