Infra-red microspectroscopy of hydrated biological systems: design and construction of a new cell with atmospheric control for the study of plant cell walls

A new hydration cell has been constructed that allows wet biological samples, or samples of controlled moisture content, to be analysed in situ using infra-red microspectroscopy. The cell has been used to show that there are minor spectral changes associated with the hydration of pectin and tomato pericarp cell walls and slightly more significant changes in onion and carrot epidermal walls. The cell was also used to show that molecular orientations of polymers, previously observed in dry cell walls, were also to be seen in hydrated walls. For cell walls of onion and carrot epidermis, it was shown that the orientations of cell wall polymers are not affected by hydration. Furthermore, the polymer orientations in cell walls of fully elongated onion epidermal cells are different from those of elongating carrot epidermis. By using the hydration cell, it is now possible to investigate both fresh samples and wet systems routinely. The applications of this to the study of biological materials with infra-red microspectroscopy are discussed.