COMPARATIVE-STUDY OF METABOLISM AND FORMS OF TRANSPORT OF PHOSPHATE BETWEEN ASCOPHYLLUM-NODOSUM AND POLYSIPHONIA-LANOSA

Polysiphonia lanosa (L.) Tandy is a marine red alga that usually grows epiphytically on the fucale Ascophyllum nodosum (L.) Le Jolis. The pr esent work was conducted in order to obtain more information on the re lationships between these two algae, especially as regards the metabol ism and long-distance transport of phosphorus. Three types of experime nts were carried out using labelled phosphorus. (1) Comparative study of the metabolism of P-32i absorbed by the tissues of each species. By means of two-dimensional chromatography and autoradiography, it was s hown that P-32i was rapidly incorporated into organic soluble compound s (adenosine triphosphate, hexose monophosphate, uridine diphosphogluc ose, phosphoenolpyruvate + phosphoglyceric acid). Although the two alg ae belong to different phylae the phosphorylated compounds were not ve ry different. The energy charges (0.72 for both species) were in the u sual range for aerobic plant tissues. On the other hand the incorporat ion of P-32i into the insoluble P0 fraction was doubled in P. lanosa c ompared to in A. nodosum (ca 80 and 40%, respectively). At the source level, the air bladder of A. nodosum, the same soluble compounds (inor ganic phosphate, P(i), adenosine triphosphate, hexose monophosphate, e tc.) represented the likely forms transported. A part of the soluble P 0 fraction may return to the P(i) fraction. (2) In translocation exper iments conducted in situ, P-32i locally injected into an air bladder m oved over long distances not only through the thallus of A. nodosum bu t also into P. lanosa. The reciprocal transfer remained unsuccessful. (3) The P-32i represented the predominant compound identified in the t wo species; this argues in favour of P(i) as the translocated form of phosphorus. Our results support the hypothesis of a parasitic rather t han a simple epiphytic relationship between the two algae.