Changes in ultrastructure and subunit composition of protein body in rice endosperm during germination.

Abstract

Changes in ultrastructure of protein bodies in subaleurone cells of rice endosperm during germination were studied by transmission electron microscopy. Thesubaleurone cells contained two different types of protein bodies: PB-I (spherical) and PB-II (crystalline).Both types of protein bodies were deconstructed during germination. But there was a considerable difference in digestibility between PB-I and PB-II. PB-II which did not have a dense core was easily digested from the central portion when germination began. At 6 days of germination, PB-II was almost deconstructed. On the other hand, PB-I which displayed concentric rings with a dense core was digested from the outside after 3 days of germination. At 9 days of germination, many kernels of the spherical protein bodies remained. Changes in subunit composition of protein bodies during germination were investigated by SDS-polyacrylamide gel electrophoresis.Protein body fractions were isolated from germinating grains at various stages by enzymatic digestion and two-phase system, then subjected to SDSpolyacrylamide gel. As germination proceeded, 15 (bx), 20 (dx), 24 (e), 35 (fx) and 37 (f3) kdaltons subunits decreased. On the other hand, 16 (b2), 21 (d2) and 36 (f2) k daltons subunits remained at the later stage of germination. Wethink that PB-I contains b2, d2 and f2 subunits and is attacked only from the outside at middle and later stages of germination by de novo protease. Onthe contrary, PB-II contains bl5 dls e, fx and f3 subunits is utilized at an early stage of germination. PB-II may possibly contain latent protease. The breakdown process ofPB-I was by exo-type digestion, on the contrary, that of PB-II was by endo-type digestion.Reserve proteins in various seeds are localized in subcellular storage particles. A predominant protein of rice, glutelin, exists in the endosperm,1>2) while globulin is mainly loca- scribed that the dense centers of protein bodies from cooked rice were not digested by human. Recently we reported the effect of cycloheximide on protein breakdown in germinating rice seeds and showed that the glutelin breakdown was affected by the inhibitor of protein synthesis and there were two types of glutelin, an easily-digested type and a hard one.U) In this paper, we demonstrate the difference in digestibility during germination between two types of protein bodies in subaleurone

Storage-protein hydrolysis and protein-body breakdown in germinatedZea mays L. seeds

“…By using electron micrographs of endosperm from germinated sorghum, Taylor et al (1985) observed protein-body degradation by progressive hydrolysis from the surface. Moreover Horikoshi and Morita (1981) C, E and G Immunocytochemical labelling of glutelin 2 in protein bodies isolated from mature (C) seeds and at 3 (E) and 6 (G) days after germination; bars=0.2 gm bodies described in the present work is thus in agreement with those described for other cereals.…”

“…It has been reported in rice (Horikoshi and Morita 1981) and sorghum (Taylor et al 1985) that the digestion of prolamin-containing protein bodies takes the form of a progressive reduction in * To whom correspondence should be addressed Abbreviations: DAP = days after pollination; SDS-PAGE = sodium dodecylsulfate-polyacrylamide gel electrophoresis size from the outer to the inner part of the organelle. The mode of degradation of protein bodies in cereals thus appears to be different from that described for dicotyledonous seeds (Pernollet 1978), where hydrolysis of storage proteins is concomitant with protein-body fusion and vacuole formation (Gifford et al 1983).…”

Ultrastructure of protein bodies in mutant rice (Oryza sativa L.) with altered storage protein composition

“…2K). The structure of deformed PB-II in K × 433 seemed to be different from deconstructed wildtype PB-II during germination, which was reported previously (Horikoshi and Morita 1982). PB-II in the Lgc1 mutant was smaller than that in Koshihikari, but the shape was not as deformed as in K × 433 (Fig.…”

Vacuolar Processing Enzyme plays an Essential Role in the Crystalline Structure of Glutelin in Rice Seed

“…PSVs containing glutelin are disappeared from the central portion by the activation of an internal latent protease at germination. The disappearance of PSVs occurs earlier than that of prolamin-containing PBs (Horikoshi and Morita 1982). Though the glutelin content in glup3 endosperm was almost the same as in the wild-type (Table 1), growth retardation of the primary leaf in glup3 seedlings was observed (Fig.…”