Sucrose-phosphate synthase was purified 13-fold from morning-glory callus cells. The molecular weight of the enzyme was estimated to be 3 .8×10⁵ by gel filtration. The optimum pH of the enzyme was 6.5. The enzyme had the optimum temperature around 45°C . EDTA slightly inhibited the enzyme activity . UTP and UDP inhibited it strongly. Ten mMMgC1₂ or 10 mM MnC1₂ activated the enzyme activity twice as much as control. Similarly, citrate at 40 mM activated it by 40%. Other inorganic salts and metabolic intermediates did not influence the enzyme activity. The K_m values for F-6-P and UDPG were 1 .3 and 2.1 mM, respectively. Based on these data, regulation of sucrose biosynthesis at a cellular level of morning-glory callus was discussed.

View full abstract

Rice starch granules are spherical to ellipsoidal in shape with varying size from 7 to 25μ in diameter. A starch granule is composed of about 20 to 60 small polygonal shaped granula of 4 to 6p in size. Scanning electron microscopy of purified starch of 12 varieties (including glutinous type) of rice grown in Niigata Prefecture revealed pits on the surface of the granula. No significant differences in starch morphology among the varieties were observed. The central portion (0.4-0.5μ) of starch granulum was stained by osmic acid differently from the exterior portion. The starch tissue was observed to be of a coarse structure. Three types of protein bodies were observed by osmium stainning; spherical granules 1-3μ in diameter with highly stained center; and spherical or square granules 1-3 p in diameter; and granules unevenly stained by osmic acid, with a diameter of about 0.5μ. Starch granula were observed to be covered with a thin electron dense matrix, which was in contact with protein-like bodies. Protein bodies were observed to be embedded in the starch granules near the surface of the endosperm. At the central portion of endosperm, starch granules and protein bodies were in contact to each other in a wedge-wise manner, and parts of the starch granules appeared to have been eroded. The pits, presumedly formed by the removal of protein bodies, were not observed in the starch granules from the white belly of rice grain.

View full abstract