Ferroni L, Baldisserotto C, Fasulo M P, Pagnoni A, Pancaldi S
Laboratory of Plant Cytophysiology, Department of Natural and Cultural Resources, University of Ferrara, Ferrara, Italy.
Protoplasma. 2004 Dec;224(3-4):167-77. doi: 10.1007/s00709-004-0072-4. Epub 2004 Dec 22.
Asynchronous cultures of wild-type Euglena gracilis were tested for their morphophysiological response to 10 mM MnSO4. Growth was only moderately slowed (15%), while oxygen evolution was never compromised. Inductively coupled plasma analyses indicated that the Mn cell content doubled with respect to controls, but no signs of localised accumulation were detected with X-ray microanalysis. Evident morphological alterations were found at the plastid level with transmission electron microscopy and confocal laser scanning microscopy. An increase in the plastid mass, accompanied by frequent aberrations of chloroplast shape and of the organisation of the thylakoid system, was observed. These aspects paralleled a decrease in the molar ratio of chlorophyll a to b and an increase in the fluorescence emission ratio of light-harvesting complex II to photosystem II, the latter evaluated by in vivo single-cell microspectrofluorimetry. These changes were observed between 24 and 72 h of treatment. However, the alterations in the pigment pattern and photosystem II fluorescence were no longer observed after 96 h of Mn exposure, notwithstanding the maintenance of the large plastid mass. The response of the photosynthetic apparatus probably allows the alga to limit the photooxidative damage linked to the inappropriately large peripheral antennae of photosystem II. On the whole, the resistance of Euglena gracilis to Mn may be due to an exclusion-tolerance mechanism since most Mn is excluded from the cell, and the small amount entering the organism is tolerated by means of morphophysiological adaptation strategies, mainly acting at the plastid level.
对野生型纤细裸藻的异步培养物进行了测试，以研究其对10 mM硫酸锰的形态生理反应。生长仅适度减缓（15%），而氧气释放从未受到影响。电感耦合等离子体分析表明，与对照相比，锰细胞含量增加了一倍，但X射线微分析未检测到局部积累的迹象。通过透射电子显微镜和共聚焦激光扫描显微镜在质体水平发现了明显的形态改变。观察到质体质量增加，同时叶绿体形状和类囊体系统组织频繁出现畸变。这些方面与叶绿素a与b的摩尔比降低以及光捕获复合物II与光系统II的荧光发射比增加平行，后者通过体内单细胞显微光谱荧光法评估。这些变化在处理24至72小时之间观察到。然而，在锰暴露96小时后，尽管质体质量仍然很大，但色素模式和光系统II荧光的改变不再观察到。光合装置的反应可能使藻类能够限制与光系统II外周天线过大不当相关的光氧化损伤。总体而言，纤细裸藻对锰的抗性可能归因于一种排斥耐受机制，因为大多数锰被排除在细胞外，而进入生物体的少量锰通过形态生理适应策略得以耐受，主要作用于质体水平。
