Li Gang, Brown Christopher M, Jeans Jennifer A, Donaher Natalie A, McCarthy Avery, Campbell Douglas A
Department of Chemistry and Biochemistry, Mount Allison University, Sackville, NB, E4L 1G7, Canada; Key Laboratory of Tropical Marine Bio-Resources and Ecology, South China Sea Institute of Oceanology, CAS, Guangzhou, 510301, China.
New Phytol. 2015 Jan;205(2):533-43. doi: 10.1111/nph.13037. Epub 2014 Sep 25.
With each cellular generation, oxygenic photoautotrophs must accumulate abundant protein complexes that mediate light capture, photosynthetic electron transport and carbon fixation. In addition to this net synthesis, oxygenic photoautotrophs must counter the light-dependent photoinactivation of Photosystem II (PSII), using metabolically expensive proteolysis, disassembly, resynthesis and re-assembly of protein subunits. We used growth rates, elemental analyses and protein quantitations to estimate the nitrogen (N) metabolism costs to both accumulate the photosynthetic system and to maintain PSII function in the diatom Thalassiosira pseudonana, growing at two pCO2 levels across a range of light levels. The photosynthetic system contains c. 15-25% of total cellular N. Under low growth light, N (re)cycling through PSII repair is only c. 1% of the cellular N assimilation rate. As growth light increases to inhibitory levels, N metabolite cycling through PSII repair increases to c. 14% of the cellular N assimilation rate. Cells growing under the assumed future 750 ppmv pCO2 show higher growth rates under optimal light, coinciding with a lowered N metabolic cost to maintain photosynthesis, but then suffer greater photoinhibition of growth under excess light, coincident with rising costs to maintain photosynthesis. We predict this quantitative trait response to light will vary across taxa.
在每一代细胞中，产氧光合自养生物都必须积累大量介导光捕获、光合电子传递和碳固定的蛋白质复合物。除了这种净合成外，产氧光合自养生物还必须通过代谢成本高昂的蛋白质水解、拆卸、重新合成和蛋白质亚基的重新组装来对抗光系统II（PSII）的光依赖性光失活。我们利用生长速率、元素分析和蛋白质定量来估计在一系列光照水平下，在两种pCO₂ 水平下生长的硅藻拟菱形藻中积累光合系统和维持PSII功能的氮（N）代谢成本。光合系统约占细胞总氮的15%-25%。在低生长光照下，通过PSII修复进行的氮（再）循环仅占细胞氮同化率的约1%。随着生长光照增加到抑制水平，通过PSII修复的氮代谢物循环增加到细胞氮同化率的约14%。在假设的未来750 ppmv pCO₂ 条件下生长的细胞在最佳光照下显示出更高的生长速率，这与维持光合作用的较低氮代谢成本相一致，但在过量光照下生长受到更大的光抑制，这与维持光合作用成本的上升相一致。我们预测这种对光的数量性状反应将因分类群而异。
