Penot, M., Hourmant, A. and Penot, M. 1993. Comparative study of metabolism nnd forms of transport of phosphate between Ascophvltum nodosum and Polvsiphoniu tanosa .Polysiphonia lanosa (L.) Tandy is a marine red alga that usually grows epiphyticiilly on the fucale AscophyUum nodosum (L.) Le Jolls. The present work was conducted in order to obtain more information on the relationships between these two jjlgae. especially as regards the metabolism and long-dislance transport of phosphorus Three types of experiments were carried out using labelled phtisphorus. (1) Comparative study of the metabolism of "'P, absorbed by the tissues ot each species. By means of two-dimensional chromatography and autoradiography, il was sho\vn that '-P, was rapidly incorporated into organic soluble compounds (adenosine triphosphate. hexose monophosphate, uridine diphosphogiucose. phosphoenolpyriLvate -p hosphoglycerif acid). Although the two aigae belong to different phylae Ihe phosphorylated compounds were not very different. The energy charges (11.72 for hoth species) were in the usual range for aerobic plant tissues. On the orhcr hand the incorporation of ^"^P, into the insoluble P,, fraction was douhled in P. lanosa compiircd to in >4. nodosum (ca 80 and 4(1%, respectively). At the source level, the air bladder of A, nodo.mm. the same soluble compounds (inorganic phosphate. P,. adenosine triphosphate. hexose monophosphate. etc.) represented the likely forms transpt>rtcd A part of the soluble P,, fraction may return to the P, fraction. (2) In transiociition experiments conducted in situ. '-P, locally injected into an air bladder moved over long distances not only through the thalius of /I. nodosum but also into P. lanosa. The reciprocal transfer remained unsuccessful. (3) The '-P, represented the predominanl compound identified in the two species: this argues in favour of P, as the translocated form of phosphorus. Our results support the hypothesis of a parasitic rather than a simple epiphytic relationship between the two algae.

Monthly measurements of the total phosphorus content in three parts of Chondrus crispus showed a gradient along the thallus with its seasonal variations. Parallel patterns of seasonal variations were observed between total phosphorus content in the growing parts of the alga (apex and middle) and dissolved inorganic phosphorus concentration in seawater. 32P-phosphorus absorbed in the alga was incorporated in organic compounds, of which 60% were water-soluble. Water-soluble phosphorylated compounds were those usually found in higher plants and other algae. With a low phosphorus content and a high specific radioactivity, the water-soluble inorganic fraction probably did not have a storage role. The water-soluble organic fraction presented the opposite characteristics; hence, it could be considered as a storage pool, together with the acid-insoluble fraction. As the seasonal pattern of the phosphorylated fractions was similar at the three parts of the alga, the phosphorus gradient along the thallus did not correspond to a qualitative or quantitative difference in storage compounds in these parts, but was still attributed to seasonal variations of phosphorus concentration in seawater and growth.

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