MEPS 218:107-114 (2001)  -  doi:10.3354/meps218107

ABSTRACT: Proteinaceous cytoplasmic inclusions with characteristic anatomical localization patterns are common in marine algae, but the function of these cell structures has not been demonstrated. Thalli of the endemic Arctic kelp Laminaria solidungula J. Agardh, cultured under N-replete conditions and examined by light and electron microscopy, were found to have a variety of cellular inclusions. One type of inclusion was shown by cytochemical methods to be proteinaceous. The protein bodies were 1 to 10 µm in diameter, had a single bounding membrane, and occurred singly or in large clusters in cells of the cortex. Intact proteinaceous inclusions were absent from N-starved thalli, although structures presumed to be depleted protein bodies had an anatomical distribution comparable to that of the protein bodies in the N-replete algae. These findings on Laminaria solidungula provide the first experimental evidence in support of the hypothesis that proteinaceous cellular inclusions in marine macroalgae constitute a nitrogen store that, like the stores of nitrate and amino acids accumulated by many algae, could be utilized during seasons when nitrate concentrations in the water column are low but when photosynthetic carbon fixation must be maximized.

KEY WORDS: Nitrogen storage · Laminaria solidungula · Algae · Protein bodies · Arctic