VISUALIZATION OF STARCH GRAINS: A RAPID OBSERVATION METHOD TO ISOLATE MUTANTS WITH DEFECTS IN STARCH GRAIN MORPHOLOGY
Starch is the most important carbohydrate for the human energy source contained in staple cereals and tubers
and is also used for food additives such as thickeners and stabilizer. Starch consists of a large number of glucose
units joined by glycosidic bonds and synthesized to form starch grains (SGs) inside plant cells. Despite the
simple glucose polymer composition of starch, SGs exhibit various morphologies depending on plant species.
The morphological variation of SGs supports the wide range of applications of starch, however the underlying
molecular mechanisms have not yet been determined. We developed an effective method for preparing thin
sections of seed endosperms without chemical fixation and conventional resin embedding that clearly visualize
subcellular starch grains. We applied this method to genetic screening to isolate rice mutants in which starch
grains were morphologically altered. In five mutants named ssg (substandard starch grain), increased numbers
of small starch grains (ssg1 to ssg3), enlarged starch grains (ssg4), and abnormal interior structures of starch
grains (ssg5) were observed. The observation method is also applicable to other cereal grains, such as barley,
wheat and maize. This method will also serve as a useful technique to study the molecular diversity of starch
grain morphologies and to monitor the cereal grain qualities.