The relative roles of chloroplastic amylolytic enzymes in intiating leaf starch degradation and metabolizing the immediate products of starch grain degradation are unknown. The roles of the extrachloroplastic amyloytic enzymes in photosynthetic tissues have yet to be elucidated. In species that have been examined, most of the amylolytic activity in photosynthetic tissues is extrachloroplastic, with B-amylase found primarily in the vacuole and a-amylase primarily in the apoplast. This research identifies the chloroplast amylolytic enzymes that can directly attack leaf starch granules, and those that cannot, and determines how these enzymes might act together to degrade leaf starch; (2) characterizes chloroplastic and extrachloroplastic a- glucosidase; and (3) verifies or disproves the localization of the primarily apoplastic a-amylase, the primarily vacuolar B-amylase, and a-glucosidases by immunohistochemistry. Starch, an end-product of higher plant photosynthesis, is stored in leaves, stems, roots and seeds as an energy reserve. During the night and other periods of reduced photosynthetic rates, starch degradation is the most important source of substrates for metabolic processes in leaves of many higher plants. Although leaf starch degradation is an important process in the regulation of plant metabolism and plant development, little is known about its regulation. Identification of the enzymes that actually attack leaf granules is a prerequisite to elucidating the mechanisms which regulate starch degradation and, therefore, carbon metabolism in plants.***//
