Mock Thomas, Hoch Nikolai
Alfred Wegener Institute for Polar and Marine Research, Am Handelshafen 12, 27570 Bremerhaven, Germany.
Photosynth Res. 2005 Sep;85(3):307-17. doi: 10.1007/s11120-005-5668-9.
Cultures of the obligate psychrophilic diatom Fragilariopsis cylindrus (Grunow) were grown for 4 months under steady-state conditions at -1 degrees C and +7 degrees C (50 micromol photons m(-2) s(-1)) prior to measurements in order to investigate long-term acclimation of photosynthesis to both temperatures. No differences in maximum intrinsic quantum yield of PS II (F(V)/F(M)) and relative electron transport rates could be detected at either temperature after 4 months of acclimation. Measurements of photosynthesis (relative electron transport rates) vs. irradiance (P vs. E curves) revealed similar values for relative light utilization efficiency (alpha = 0.57 at -1 degrees C, alpha = 0.60 at +7 degrees C) but higher values for irradiance levels at which photosynthesis saturates (E(K)) at -1 degrees C and, therefore, higher maximum photosynthesis (P(MAX) = 54 (relative units) at -1 degrees C, P(MAX) = 49 at +7 degrees C). Nonphotochemical quenching (NPQ) measurements at 385 mumol photons m(-2) s(-1) indicated higher (37%) NPQ for diatoms grown at -1 degrees C compared to +7 degrees C, which was possibly related to a 2-fold increase in the concentration of the pigment diatoxanthin and a 9-fold up-regulation of a gene encoding a fucoxanthin chlorophyll a,c-binding protein. Expression of the D1 protein encoding gene psbA was ca. 1.5-fold up-regulated at -1 degrees C, whereas expression levels of other genes from Photosystem II (psbC, psbU, psbO), as well as rbcL, the gene encoding the Rubisco large subunit were similar at both temperatures. However, a 2-fold up-regulation of a plastid glyceraldehyde-P dehydrogenase at -1 degrees C indicated enhanced Calvin cycle activity. This study revealed for the first time that a polar diatom could efficiently acclimate photosynthesis over a wide range of polar temperatures given enough time. Acclimation of photosynthesis at -1 degrees C was probably regulated similarly to high light acclimation.
为了研究光合作用对这两种温度的长期适应性，在测量之前，将专性嗜冷硅藻纤细角毛藻（格鲁诺）的培养物在-1℃和+7℃（50微摩尔光子·米-2·秒-1）的稳态条件下培养4个月。经过4个月的适应后，在这两种温度下均未检测到PS II的最大内在量子产率（F(V)/F(M)）和相对电子传递速率的差异。光合作用（相对电子传递速率）与光照强度的测量（P对E曲线）显示，相对光利用效率的值相似（-1℃时α = 0.57，+7℃时α = 0.60），但-1℃时光合作用饱和时的光照强度水平（E(K)）值更高，因此，最大光合作用也更高（-1℃时P(MAX) = 54（相对单位），+7℃时P(MAX) = 49）。在385微摩尔光子·米-2·秒-1下的非光化学猝灭（NPQ）测量表明，与+7℃下生长的硅藻相比，-1℃下生长的硅藻的NPQ更高（37%），这可能与色素硅藻黄质浓度增加2倍以及编码岩藻黄质叶绿素a,c结合蛋白的基因上调9倍有关。编码D1蛋白的基因psbA的表达在-1℃时上调了约1.5倍，而来自光系统II的其他基因（psbC、psbU、psbO）以及编码Rubisco大亚基的基因rbcL在两种温度下的表达水平相似。然而，-1℃时质体甘油醛-P脱氢酶上调2倍表明卡尔文循环活性增强。这项研究首次揭示，在有足够时间的情况下，极地硅藻能够在很宽的极地温度范围内有效地适应光合作用。在-1℃下光合作用的适应可能与高光适应的调节方式类似。
