Centre of Geometric Biology, School of Biological Sciences, Monash University, Melbourne, Vic., 3800, Australia.
Department of Marine Biology and Aquaculture, ARC Centre of Excellence for Coral Reef Studies, James Cook University, Townsville, Qld, 4811, Australia.
New Phytol. 2018 Jul;219(1):449-461. doi: 10.1111/nph.15163. Epub 2018 Apr 15.
Cell size correlates with most traits among phytoplankton species. Theory predicts that larger cells should show poorer photosynthetic performance, perhaps due to reduced intracellular self-shading (i.e. package effect). Yet current theory relies heavily on interspecific correlational approaches and causal relationships between size and photosynthetic machinery have remained untested. As a more direct test, we applied 250 generations of artificial selection (c. 20 months) to evolve the green microalga Dunaliella teriolecta (Chlorophyta) toward different mean cell sizes, while monitoring all major photosynthetic parameters. Evolving larger sizes (> 1500% difference in volume) resulted in reduced oxygen production per chlorophyll molecule - as predicted by the package effect. However, large-evolved cells showed substantially higher rates of oxygen production - a finding unanticipated by current theory. In addition, volume-specific photosynthetic pigments increased with size (Chla+b), while photo-protectant pigments decreased (β-carotene). Finally, larger cells displayed higher growth performances and F /F , steeper slopes of rapid light curves (α) and smaller light-harvesting antennae (σ ) with higher connectivity (ρ). Overall, evolving a common ancestor into different sizes showed that the photosynthetic characteristics of a species coevolves with cell volume. Moreover, our experiment revealed a trade-off between chlorophyll-specific (decreasing with size) and volume-specific (increasing with size) oxygen production in a cell.
细胞大小与浮游植物物种的大多数特征相关。理论预测，较大的细胞应该表现出较差的光合作用性能，这可能是由于细胞内自我遮光减少（即封装效应）。然而，当前的理论严重依赖于种间相关性方法，并且大小与光合作用机制之间的因果关系尚未得到检验。作为更直接的测试，我们应用了 250 代的人工选择（约 20 个月）来使绿色微藻杜氏盐藻（Chlorophyta）朝着不同的平均细胞大小进化，同时监测所有主要的光合作用参数。进化出更大的大小（体积差异超过 1500%）导致每叶绿素分子的氧气产量降低 - 正如封装效应所预测的那样。然而，大进化的细胞表现出明显更高的氧气产生速率 - 这一发现与当前的理论预期不符。此外，体积特异性的光合色素（Chla+b）随着大小的增加而增加，而光保护色素（β-胡萝卜素）则减少。最后，较大的细胞显示出更高的生长表现和 F/F、快速光曲线（α）的更陡峭斜率以及更高连通性（ρ）的更小的光捕获天线（σ）。总的来说，将一个共同的祖先进化成不同的大小表明，一个物种的光合作用特征与细胞体积共同进化。此外，我们的实验揭示了细胞中叶绿素特异性（随大小减小）和体积特异性（随大小增加）氧气产生之间的权衡。
