Water Status Changes in Shoots of a Seaweed Ascophyllum nodosum at Subzero Temperatures.

The gradient freezing and NMR spectroscopy were used to study the physical state of water in apices of the intertidal seaweed Ascophyllum nodosum at freezing temperatures. In the apices exposed to temperatures below –10°C, two fractions of bound water were revealed. The slow (T₂ ∼ 50 ms) fraction of bound water was completely frozen at –25°C, and its freezing rate was temperature-sensitive. This fraction was apparently associated with protoplasmic water and cell-wall polysaccharides. The fast fraction (T₂ < 10 ms) of bound water was presumably due to water-soluble globular proteins. The freezing rate for this fraction depended on neither the temperature nor the amount of water. The presence of unfrozen water in apical cells at –40°C was demonstrated. The role of this water fraction in maintaining the native structure of biomacromolecules and apex survival is discussed. [ABSTRACT FROM AUTHOR]