Nitrogen Metabolism in Lichens Iv. The Nitrogenase Activity of the Nostoc Phycobiont in Peltigera Canina

Summary The content of the blue‐green alga phycobiont, Nostoc sp. in the lichen Peltigera canina has been estimated using various techniques and represents on average 2.7% of the total thallus nitrogen. Expressed in terms of cell numbers, this represents approximately 3 × 106 cells cm2, mature thallus. The nitrogenase activity, expressed as nil ethylene evolved/minute/mg Sostoc protein, varies considerably with the thallus sample, but a mean value of 10, considerably greater than that in free‐living Nostoc, has been found. The nitrogenase activity of the algal cells is particularly sensitive to disturbance of the thallus structure and the implications of these findings are discussed.