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首页> 外文期刊>european journal of phycology >Photoacclimation by the Antarctic flagellatePyramimonassp. (Prasinophyceae) in response to iron limitation
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Photoacclimation by the Antarctic flagellatePyramimonassp. (Prasinophyceae) in response to iron limitation

机译：南极鞭毛的光驯化Pyramimonassp。（Prasinophyceae）对铁限制的反应

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In this study we tested the hypothesis that iron limitation suppresses photoacclimation in cultures of the Antarctic flagellatePyramimonassp. The cultures were exposed to two different irradiances under iron-rich and iron-poor conditions. Light-harvesting capacity was determined by assessing the pigment composition and measuringin vivoabsorption spectra. Light utilization efficiency (#x3B1;) was determined from photosynthesis versus irradiance curves. The quantum yield of photosynthesis (#x3C6;m) was calculated using #x3B1; and the absorption spectra. Iron limitation led to commonly observed changes in cells ofPyramimonas, that is, a decrease in cellular pigment content and a reduction in cellular carbon and nitrogen quota. A reduction in #x3B1;cellfollowed a decrease in #x3C6;mand light-harvesting capacity. Interpretation of the effects of iron limitation was different when considered on a carbon basis. Because iron limitation resulted in a decrease in cellular carbon content, the carbon-specific absorption coefficient was not affected. Consequently, the observed decrease in #x3B1;Cwas mainly due to the decrease in #x3C6;m, showing that iron limitation did not control light utilization via pigment synthesis but exerted control on energy transfer. This is supported by the findings that at high irradiance a shift in pigment ratios within the total pool of violaxanthin, antheraxanthin and zeaxanthin towards zeaxanthin, which is indicative of photoacclimation to high irradiance, was observed for iron-replete cells as well as for iron-depleted cells. In contrast to what is generally hypothesized, the effects of iron limitation were not enhanced at low irradiance. Low irradiance led to an increase in the cellular light-harvesting pigment content. This increase was less pronounced in iron-depleted cells than in iron-replete cells. However, looking at the light-harvesting capacity of the cells on a carbon basis, it was found that iron-depleted cells responded similarly to iron-replete cells. We therefore conclude that the light-harvesting capacity was governed by light conditions and not by iron limitation. In addition to the increase in absorption capacity at low irradiance, an increase in light utilization efficiency was measured, again under both iron-rich and iron-poor conditions. Notably, the relative increase in #x3B1;Cwas strongest in iron-depleted cells. Photoacclimation was clearly demonstrated by normalizing #x3B1; to chla. For iron-replete cells, #x3B1;chlwas highest at high irradiance. In contrast, for iron-depleted cellsachlwas highest at low irradiance. We argue that iron-depleted cells can photoacclimate to low irradiance by a reduction in the #x2018;package effect#x2019; and reducing growth rates.
机译：在这项研究中，我们测试了铁限制抑制南极鞭毛Pyramimonassp培养物中光驯化的假设。在富铁和贫铁条件下，将培养物暴露于两种不同的辐照度。通过评估颜料组成和测量体内吸收光谱来确定光捕获能力。光利用效率 （α） 由光合作用与辐照度曲线确定。利用α和吸收光谱计算光合作用的量子产率（φm）。铁的限制导致了吡胺酮类细胞中普遍观察到的变化，即细胞色素含量降低，细胞碳和氮配额减少。αcell的减少伴随着φmand光收集能力的降低。当以碳为基础考虑时，对铁限制影响的解释是不同的。由于铁限制导致细胞碳含量降低，因此碳比吸收系数不受影响。因此，αCwas的降低主要是由于φm的降低，表明铁限制没有通过色素合成控制光利用，而是控制了能量转移。研究结果支持了这一点，即在高辐照度下，紫黄质、花黄质和玉米黄质总池中的色素比例向玉米黄质的转变，这表明对高辐照度的光驯化，对于铁饱和的细胞。与通常假设的相反，铁限制的影响在低辐照度下并未增强。低辐照度导致细胞光捕获色素含量增加。这种增加在缺铁细胞中不如在缺铁细胞中明显。然而，在碳基上观察细胞的光收集能力时，发现缺铁细胞的反应与富含铁的细胞相似。因此，我们得出结论，光的收集能力是由光条件决定的，而不是由铁限制决定的。除了在低辐照度下吸收能力的增加外，还测量了光利用效率的提高，同样是在富铁和贫铁条件下。值得注意的是，αC的相对增加在缺铁细胞中最强。通过将α归一化为 chla，可以清楚地证明光驯化。对于富含铁的细胞，αchl在高辐照度下最高。相反，对于贫铁细胞，在低辐照度下最高。我们认为，缺铁细胞可以通过减少“包装效应”和降低生长速率来光适应低辐照度。

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