Turnover of the intracellular mannitol pool of Fucus spiralis L. (fucales, phaeophyta) during osmotic shock

Abstract

13C {1H} nuclear magnetic resonance spectroscopy has been used to study the turnover of the low-molecular weight carbohydrate mannitol in the marine brown alga Fucus spiralis L. During incubation of plants in seawater medium with 13C enriched bicarbonate, all of the NMR-visible 13C appeared in mannitol; no significant 13C-labelling of laminaran was observed in seawater, in a hypo-saline or in a hyper-saline medium. Pulse-chase experiments showed that intracellular mannitol was subject to turnover (half-time {reversed tilde equals}20 h), the rate of carbon assimilation into mannitol being slightly greater than the dissimilation rate, possibly due to net mannitol synthesis during growth.Fucus spiralis was conservative in the use of mannitol as an intracellular osmoticum. In a hypo-saline medium, mannitol showed no substantial change while potassium, the major cellular cation, was reduced. In contrast, mannitol increased substantially over a 12 h incubation period in a hyper-saline medium, whereas potassium content remained constant.Mannitol assimilation and dissimilation rates were not affected significantly by transfer to a hypo-saline medium. The increased mannitol content of plants incubated in a hyper-saline medium appeared to be due to a significant increase in the mannitol assimilation rate. © 1989 Oxford University Press.