Trapping and Nursing Factors and Photosynthetic Activity of the Photobiont Cyanobacteria in Cyanomorph Thalli of Lichen

Abstract

There seems to be two important factors for trapping and/or nursing the cyanobacterial symbiont cells in the thalli of Peltigera polydactylon. One is the nitrogen nutrition probably produced by the host fungi. The cyanobacteria isolated from P. polydactylon contain heterocyst cells endowed with nitrogen fixation especially under the nitrate deficiency. However, the typical spectra derived from the heterocyst, which lacks functional photosystem II, was not observed in the thalli of P. polydactylon. Another candidate is carbon dioxide or bicarbonate probably supplied with fungi cells. During the strong light illumination, oxygen evolution activity of the isolated cyanobacteria decreased. With incubation of bicarbonate, however, the activity of the isolated cyanobacteria did not decrease, which was similar to the activities of the thalli of P. polydactylon. Protection from the photoinhibition of photosynthetic apparatus by the strong light was observed in the thalli of P. polydactylon.