Storage carbohydrates and abscisic acid contents in Laminaria hyperborea are entrained by experimental daylengths

The storage carbohydrates mannitol and laminaran and the angiosperm phytohormone abscisic acid (ABA) were analysed in Laminaria hyperborea. Sporophytes were cultivated in different experimental daylength conditions. Seasonal fluctuations of mannitol, laminaran and ABA were entrained by experimental daylength cycles with periods of T = 12 and T = 6 months and were related to the respective growth rates. In 8 h light per day, which induced continuous growth of sporophytes, all three compounds showed constant levels for more than 60 weeks. Culture in 16 h light per day induced minimal growth, which was briefly interrupted by the formation of miniature blades. During the phase of minimal growth, storage carbohydrates and ABA remained at high levels. In spite of the very short, indistinct growth phase, the concentrations of mannitol, laminaran and ABA decreased distinctly. The new blades ceased growth soon after their induction and the concentrations of all three compounds increased again.