STORAGE OF NITROGEN IN THE FORM OF PROTEIN BODIES IN THE KELP LAMINARIA SOLIDUNGULA

Pueschel, C. M. 1 & Korb, R. E. 21 Department of Biological Sciences, State University of New York at Binghamton, Binghamton, NY 13902 USA; 2 British Antarctic Survey, High Cross, Madingley Road, Cambridge CB3 0ET, UK Proteinaceous cytoplasmic inclusions with characteristic anatomical localization patterns are common in marine algae, but the function of these cell structures has not been demonstrated. Microscopic examination of the endemic Arctic kelp, Laminaria solidungula J. Agardh, grown under nitrogen‐limited and nitrogen‐replete culture conditions revealed a variety of unusual cell structures. Some were present in both experimental treatments, but others occurred intact only under N‐replete conditions. Cortex cells of N‐replete specimens contained abundant single membrane‐bounded cytoplasmic inclusions, 1‐10 μm in diameter. Cytochemical staining procedures showed that these inclusions were proteinaceous but they did not reveal a carbohydrate component. Intact proteinaceous inclusions were absent from cells of the N‐starved samples; however, structures presumed to be depleted protein bodies had an anatomical distribution comparable to that of the protein bodies in the N‐replete algae. The proteinaceous inclusions in L. solidungula may represent a nitrogen store, which like the stores of nitrate and amino acids present in many algae, can be utilized during the summer months when water column nitrate concentrations are low but when photosynthetic carbon fixation must be maximized. Storage of nitrogen in the form of protein bodies has the advantage of being osmotically inactive.