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Starch - Metabolism and Structure
Rapid progress of research in recent years on the biosynthesis, degradation, and
structure of starch produced in photosynthetic and non-photosynthetic tissues
from a variety of plant species and in algae, including land plants and green
algae (Chloroplastida), red algae (Rhodophyceae), and cyanobacteria, lead us to
understand the whole scope of the specific metabolic systems in plants. At the same
time we must revise our earlier concept of starch-related metabolism by dealing
with the newly revealed dynamism of regulation of starch biosynthesis.
Genome analysis indicates that higher plants have evolved two different starch
biosynthetic processes in photosynthetic and non-photosynthetic tissues by differentiation of key enzymes for starch biosynthesis, i.e., starch synthase, starch
branching enzyme, and starch debranching enzyme, into multiple isozymes having
specific catalytic properties. Concomitantly, plants have refined the fine structure
of amylopectin, the major component of starch, so that it can be densely packed
into the semi-crystalline granules having distinct size and morphology depending
on plant species and tissues
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