Departamento de Biología Vegetal II, Facultad de Farmacia, Universidad Complutense, Madrid, 28040 Spain.
Ann Bot. 2012 Aug;110(3):555-63. doi: 10.1093/aob/mcs108. Epub 2012 May 30.
Cyanolichens are usually stated to be bipartite (mycobiont plus cyanobacterial photobiont). Analyses revealed green algal carbohydrates in supposedly cyanobacterial lichens (in the genera Pseudocyphellaria, Sticta and Peltigera). Investigations were carried out to determine if both cyanobacteria and green algae were present in these lichens and, if so, what were their roles.
The types of photobiont present were determined by light and fluorescence microscopy. Small carbohydrates were analysed to detect the presence of green algal metabolites. Thalli were treated with selected strengths of Zn(2+) solutions that stop cyanobacterial but not green algal photosynthesis. CO(2) exchange was measured before and after treatment to determine the contribution of each photobiont to total thallus photosynthesis. Heterocyst frequencies were determined to clarify whether the cyanobacteria were modified for increased nitrogen fixation (high heterocyst frequencies) or were normal, vegetative cells.
Several cyanobacterial lichens had green algae present in the photosynthetic layer of the thallus. The presence of the green algal transfer carbohydrate (ribitol) and the incomplete inhibition of thallus photosynthesis upon treatment with Zn(2+) solutions showed that both photobionts contributed to the photosynthesis of the lichen thallus. Low heterocyst frequencies showed that, despite the presence of adjacent green algae, the cyanobacteria were not altered to increase nitrogen fixation.
These cyanobacterial lichens are a tripartite lichen symbiont combination in which the mycobiont has two primarily photosynthetic photobionts, 'co-primary photobionts', a cyanobacterium (dominant) and a green alga. This demonstrates high flexibility in photobiont choice by the mycobiont in the Peltigerales. Overall thallus appearance does not change whether one or two photobionts are present in the cyanobacterial thallus. This suggests that, if there is a photobiont effect on thallus structure, it is not specific to one or the other photobiont.
蓝藻地衣通常被认为是二分体的（真菌共生体加上蓝藻光合生物）。分析表明，在所谓的蓝藻地衣（拟皮壳属、石地衣属和 Peltigera 属）中存在绿藻碳水化合物。进行了调查，以确定这些地衣中是否存在蓝藻和绿藻，如果存在，它们的作用是什么。
通过光和荧光显微镜确定存在的光生物类型。分析小碳水化合物以检测绿藻代谢物的存在。用选定强度的 Zn(2+)溶液处理叶状体，该溶液停止蓝藻但不停止绿藻光合作用。在处理前后测量 CO(2)交换，以确定每个光合生物对整个叶状体光合作用的贡献。确定异形胞频率以澄清蓝藻是否为增加固氮而改变（异形胞频率高）或为正常的营养细胞。
几种蓝藻地衣在叶状体的光合层中存在绿藻。绿藻转移碳水化合物（赤藓糖醇）的存在以及用 Zn(2+)溶液处理后叶状体光合作用不完全抑制表明，两个光合生物都为地衣叶状体的光合作用做出了贡献。异形胞频率低表明，尽管存在相邻的绿藻，但蓝藻并未改变以增加固氮。
这些蓝藻地衣是一个三分体地衣共生体组合，其中真菌共生体有两个主要的光合光生物，“共同主要光生物”，一个蓝藻（优势）和一个绿藻。这表明 Peltigerales 中真菌共生体在光合生物选择方面具有很高的灵活性。无论蓝藻叶状体中存在一个还是两个光合生物，整个叶状体的外观都不会改变。这表明，如果有光合生物对地衣结构的影响，它不是针对一个或另一个光合生物的。
