关键词: 大麦, 胚乳, 淀粉体, 小淀粉粒, 复粒淀粉, 单粒淀粉

Abstract: Mature starchy endosperm of barley is mainly composed of starch. The structural characteristics and physicochemical properties of barley starch differ with granule size, which is important in final product applications of barley flours. To produce barley cultivars with predominantly large or small starch granules, it is necessary to understand the development of large and small starch granules during barley endosperm development. However, only large starch granule in barley has been studied currently, while little information is available on small starch granule development. In this study, we used Yangsimai 3 as the material to investigate small starch granule development in barley endosperm. Starch granules in barley mature endosperm showed a three-size distribution after differential sedimentation. The average long axis of A-, B-, and C-type starch granules was 16.1, 7.9, and 2.6 mm, and their percentage in total starch weight was 87.2%, 11.9%, and 0.9%, respectively. Large starch granule (A-type) increased quickly in size with approximate maximum diameter at 12 days after ear stem emerging from flag leaf sheath (DAE). The number of large starch granules in endosperm cell changed little after 16 DAE. Small starch granules (B- and C-types) initi-ated at 12 DAE and increased quickly in number from 12 to 20 DAE. After 20 DAE, the magnitude of increase in number of small starch granules reduced. Scanning electron micrographs indicated that large starch granules showed a disk shape and small starch granules showed a spherical or irregularly polygonal shape. Endosperm cells had large amyloplast that exhibited protrusions from envelope at 10 DAE. Spherical small amyloplast appeared at 12 DAE and increased quickly in number at 20 DAE. Some small amyloplasts showed polygonal shape at 24 DAE. Many irregularly polygonal small starch granules were observed around large starch granules after 28 DAE. Transmission electron micrographs with conventional glutaraldehyde-osmium tetroxide fixation showed that early endosperm cells contained amyloplasts that contained single starch granule. Large amyloplasts with large starch granules divided and increased in number through binary fission at 12 DAE. One large amyloplast had only one large starch gra- nule. The envelopes of large and small amyloplasts were difficultly observed after 12 DAE. Transmission electron micrographs with potassium permanganate fixation showed a distinct endomembrane organization, in particular, the structure associations of the amyloplast envelope with amyloplast proliferation during endosperm development. Endosperm cells had large amyloplasts that exhibited protrusion at 12 DAE, and some of the protrusions contained small starch granules. Small amyloplasts with small starch granules formed new small amyloplasts to produce small starch granules by the way of protruding of their envelopes at 16 DAE. Many small starch granules formed and developed in one small amyloplast. With small starch granules development in one small amyloplast, some small starch granules became irregularly polygonal shape when they enlarged close to one another. The amyloplast envelope began to degrade and released starch granules into cell matrix when amyloplast was full of starch granules. The above results showed that small amyloplasts came from the protrusion of amyloplast envelopes. Many small starch granules, which were compound starch granules, formed and developed in one small amyloplast.

Key words: Barley, Endosperm, Amyloplast, Small starch granule, Compound starch granule, Single starch granule