Measurement of porosity in very small samples of plant tissue

The relative volume of internal gas spaces (i.e., porosity) of the shoot and roots of a plant largely determines its resistance to flooding, as oxygen may diffuse through these cavities from non-flooded parts of the plant into the submerged tissues. The current techniques to measure porosity either need relatively large amounts of plant tissue (200 mg per sample), or are timeconsuming and not sufficiently accurate for specific types of plant material. These limitations were the reason to develop a new method of porosity measurement. Small segments of roots were taken from freshly harvested plants, placed in a two-piece hard gelatin capsule and weighed on a microbalance. The root segments were subsequently infiltrated with water under vacuum, blotted carefully and weighed again. Using the increase in weight and the specific weight of infiltrated tissue, derived from a larger sample of roots, it was possible to calculate the porosity of individual root segments as small as 3–5 mg with a length of 5 mm. The new method combines this use of small samples with a high accuracy, and proved useful for a variety of plant species. Porosity data obtained with this method will improve our knowledge of small-scale processes such as aerenchyma development in root tips.