蛋白核小球藻生长和无机碳利用对不同光照强度和CO_2浓度的响应

Response of growth and inorganic carbon utilization to different light and CO_2 levels in Chlorella pyrenoidosa

为了探讨光照强度和CO_2浓度对蛋白核小球藻（Chlorella pyrenoidosa）生长、无机碳利用的复合效应,丰富绿藻中无机碳浓缩机制的资料,该文设置两种光照强度（40和120μmol photons×m–2×s–1）和两种CO_2浓度（0.04%和0.16%）组合成4种条件,比较了蛋白核小球藻生长、无机碳浓度、pH补偿点、光合放氧速率、碳酸酐酶（CA）活性和α-CA基因转录表达对这4种培养条件的响应。结果发现：蛋白核小球藻在高光强高CO_2浓度组生长最快;低光强高CO_2浓度组培养体系中总无机碳浓度为1 163.3μmol×L–1,显著高于其他3组;高光强低CO_2浓度组藻的p H补偿点最高（9.8）,而低光强高CO_2浓度组藻的p H补偿点最低（8.6）;低光强高CO_2浓度组藻的最大光合速率（Vmax）和最大光合速率一半时的无机碳浓度（K0.5）最高,分别是其他3组的1.28-1.91倍和1.61-2.00倍;高光强低CO_2浓度组藻的胞外CA活性最高;而低光强低CO_2浓度组藻的胞外α-CA基因表达量显著高于其他3组。以上结果表明低CO_2浓度可促进蛋白核小球藻的pH补偿点和无机碳亲和力的提高,诱导胞外CA活性及α-CA基因的表达;该藻主要以HCO_3~–为无机碳源,其对无机碳的利用受光照的调节。

Aims Carbon concentrating mechanism （CCM） is one of the important contents in algal physiology and ecology. Numerous studies have been carried out in eukaryotic and prokaryotic algae, but the information on economic microalga Chlorella pyrenoidosa （Chlorophyta） is limited. Our purpose is to explore the composite effect of light and CO2 on growth, inorganic carbon utilization in C. pyrenoidosa, and enrich the data on CCM in green algae. Methods Two light intensities （40 and 120 μmol photons？m–2？s–1） and two CO2 concentrations （0.04% and 0.16%） were combined into four treatments, and then the algal growth, inorganic carbon concentration, pH com-pensation point, photosynthetic oxygen evolution rate, carbonic anhydrase （CA） activity and α-CA gene expres-sion were investigated. Important findings Chlorella pyrenoidosa grew fastest under the high-light and high-CO2 condition. The total inorganic carbon concentration under low-light and high-CO2 group was 1 163.3 μmol＆#183;L–1, which was signifi-cantly higher than that of other three groups. The alga had the maximal pH compensation point of 9.8 under the high-light and low-CO2 condition, and the minimal pH compensation point of 8.6 under the low-light and high-CO2 condition. The maximum photosynthetic rate （Vmax） and inorganic carbon concentration in half maxi-mum photosynthetic rate （K0.5） in the low-light and high-CO2 group were the highest, which were 1.28–1.91 times and 1.61–2.00 times of that in other three groups, respectively. The highest activity of extracellular CA was de-tected in the high-light and lower-CO2 group. However, α-CA gene expression reached the maximum under the low-light and low-CO2 condition. The results indicated that the low CO2 level could increase the algal pH com-pensation point, photosynthetic inorganic carbon affinity, and induce the external CA activity and α-CA gene＆amp;nbsp;expression in C. pyrenoidosa. HCO3– was used as the primary inorganic carbon source, and the inorganic carbon utilization was also regulated by light in C. pyrenoidosa.