Starch determination in plant tissues using a computerized image analysis system

Abstract

Starch is the main reserve compound in woody plant species. Changes in starch content are clear indicators of a variety of plant developmental processes. Thus, carbohydrate extraction and other analytical methods have been widely used to measure changes in starch content. However, the use of these methods can be limited by the fact that starch is often compartmentalized in very small portions of tissue. While changes in these small structures can be histochemically characterized and localized under the microscope, they cannot be quantified. As an alternative, an image analysis system attached to a microscope has been developed to detect quantitative variations in starch in particular tissues or cells. The system has been successfully used to study the differences in starch content of sections from pistillar structures in apricot (Prunus armeniaca L.). The procedure is based on the measurement of the optical density of black and white images obtained from the microscope. Two staining methods, I2KI (potassium iodide‐iodine) and PAS (periodic acid Schiff's reagent), and two embedding techniques, paraffin and JB4 plastic resin, were compared. The best results were obtained using I2KI‐stained sections of paraffin‐embedded material. Since the procedures used are non‐destructive for the tissues studied, additional information can be obtained, on the same section, by the subsequent use of additional stains. The method described here can be used to detect quantitative variations in starch content under the microscope in different plant tissues and thus to follow changes in starch reserves in small structures.