New Ultrastructural Aspects of Pyrenoids of the Lichen Photobionttrebouxza(microthamniales, Chlorophyta)1

The pyrenoid structureof Trebouxia,a photobiont of two lichen species, Umbilicaria cinereorufescens (Schaer.) Frey andParmelia sulcataTaylor, was investigated. In both lichen species, the pyrenoid of the photobiont exhibited straight, unbranched, long or short tubules. In the first lichen species, multiple pyrenoids were observed occasionally, while in the second one, homogeneous masses, called protein bodies, appeared between the thylakoids. These protein bodies were previously observed in some other species of the family Umbilicariaceae. Serial sections from single pyrenoids showed that tubules of theImpressa‐type pyrenoid were closely associated with pyrenoglobuli. The three‐dimensional reconstruction of a complete chloroplast of aP. sulcataalgal cell showed that the protein bodies were spatially separate structures. Immunolocalization techniques to detect the presence of ribulose‐bisphosphate carboxylase (Rubisco) in the chloroplast showed that this enzyme was present primarily in the pyrenoid matrix. When protein bodies were present in the chloroplast, Rubisco appeared to be localized in these structures. The presence of pyrenoid satellites and protein bodies with reactivity to anti‐Rubisco may be related to the nutritional conditions of the thalli.